ECEstream: 555 Timer IC

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Water Pump Controller

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A water pump controller senses the level of water in a tank and drives the water pump. The circuit described here is built around timer IC1 (555). When the water level of tank goes below the low level marked by 'L' the voltage at pin 2 of IC1 becomes low. As a result, internal SR-flip-flop of IC1 resets and its output goes high. This high output pin 3 of IC1 drives relay driver transistor T1 (BC547) and energises relay RL1. Water pump gets mains power supply through N/O contacts of the relay and is powered on. It starts filling water in the tank.</div>
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When the water level goes high and reaches the high level marked by 'H', the voltage at pin 6 of IC1 also goes high. As a result, internal SR-flip-flop of IC1 sets and its output goes low. This low output pin 3 of IC1 cuts off relay driver transistor T1 and de-energises relay RL1. Water pump disconnects from the mains power supply through n/c contacts of relay and goes off. This stops the water flow.</div>
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Use 12V battery or 12V adaptor to operate the circuit. Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Use three-sensor (thick conductive wire) and fit into the tank ensuring that 12V sensor touches the bottom and low-level sensor remains just above the bottom. High level sensor should be placed at a height till where the water needs to be filled. The circuit is economical, highly reliable and can be easily constructed.</div>
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<img alt="Water Pump Controller Circuit" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4aHX8aTHKz0PVMTrIY31E_N0UAedMrwza-1qJiJT_vxGShj8jhc1o5AJyPKeEcbc6M8QEyYnqedirRWFixOE9UnoVmZWzrf3ZQQQAlkLIoXCCGwd-Q7t9JwbQxeq83vdf16Tvqge_27hyphenhyphen/s1600/Water+Pump+Controller.jpg" title="Water Pump Controller Circuit" /></div>
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Water Pump Controller

Water Pump Controller

A water pump controller senses the level of water in a tank and drives the water pump. The circuit described here is built around timer IC...

Linear Timer For General Use

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This simple timer can be used to control any electrical appliance that needs to be switched off after certain time, like a small heater or a boiler, provided the relay-switch parameters meet the requirements of that appliance. It uses low-cost components and combines digital precision with simple analogue control, providing long timing durations without the use of high-valued resistors or capacitors.</div>
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The circuit is built around CD4040, LM358, CD4069 and NE555. The working of the timer is quite simple, based on digital-to-analogue conversion (DAC). The counter (CD4040) runs the DAC (formed by R-2R ladder resistors R2-R23 and following operational amplifier IC3 (N1 and N2)). The second op-amp (N2) compares the DAC output with a variable voltage set by VR1 according to the time requirement. The larger the voltage set, the longer the time duration and higher the count, larger the DAC output voltage and vice versa.</div>
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As soon as the count of the counter becomes large enough to produce slightly larger voltage than the voltage set by potentiometer VR1, the second op-amp (N2) goes low to cut-off transistor T1 and reset the clock generator built around NE555 (IC2). The clock generator thus produces no further pulses and the counter remains static at this particular count indefinitely.</div>
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Pressing the reset switch (S1) resets the counter (IC1). Thus the voltage from the DAC falls to zero causing the second op-amp (N2) to go high, enabling clock generator IC2 and making transistor T1 conduct. The timer again activates and simultaneously the relay energises.</div>
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A diode is used in parallel to the relay coil to suppress the reverse induced voltage. The maximum timing acheivable is dependent on the frequency of the clock generator and the supply voltage:</div>
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<img border="0" height="95" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgiZ30MP-I7eoZ21YsgjSLU3CZX-IBFKCyOKcEQS5cAdCnhAkWXNSlqlde5u6NiLIerLpFtSHCxB9W1PuaG_muv6wlz_PtTMSZ7pyI2XpV5f6q7qskCh8qQkCm5Nd0XmZNU4PDDymgPRCOm/s320/aaa.png" width="320" /></div>
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This happens because the ratio <span style="font-family: inherit;"><span style="background-color: white;">V</span><sub style="background-color: white;">OPmax</sub><span style="background-color: white;">/V</span></span> is a slow function of supply voltage. <span style="background-color: white;">V</span><sub style="background-color: white;">OPmax</sub> increases with increase in V so this ratio varies slowly with supply voltage and can be assumed to be constant.</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihRdgSHW5OTIvrPtVMwbl68RdJEh2wHhTnRiovBf7eu4IJMO_A4lS-YeeqbRg-5y_dSB7uZNtA0UbeQ8wktE1Mqe4prugfgj0ChxZov0UPSyrbFUCRHsN_vPLODPsKmEUpa2Zjgg8WZaNq/s1600/Linear+Timer+For+General+Use.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="Linear Timer For General Use" border="0" height="465" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihRdgSHW5OTIvrPtVMwbl68RdJEh2wHhTnRiovBf7eu4IJMO_A4lS-YeeqbRg-5y_dSB7uZNtA0UbeQ8wktE1Mqe4prugfgj0ChxZov0UPSyrbFUCRHsN_vPLODPsKmEUpa2Zjgg8WZaNq/s640/Linear+Timer+For+General+Use.jpg" title="Linear Timer For General Use Circuit" width="640" /></a></div>
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So for F=1 Hz and supply voltage V=15 volts, the maximum achievable timing is 3686 seconds, which is slightly more than one hour. Frequencies as low as 0.1 Hz can be easily generated using the 555 timer. The timer can also withstand fluctuations in the supply voltage.</div>
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Here in the circuit, at 12V, resistors R24, R25 and capacitor C2 produce around 1.47 Hz frequency and the relay de-energises after around 1.5 hours to switch off the load. At the same time, the alarm built around IC4 sounds indicating that the appliance is off. The circuit can be assembled on any general-purpose PCB.</div>
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Linear Timer For General Use

Linear Timer For General Use

This simple timer can be used to control any electrical appliance that needs to be switched off after certain time, like a small heater or...

Speed Checker for Highways

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While driving on highways, motorists should not exceed the maximum speed limit permitted for their vehicle. However, accidents keep occurring due to speed violations since the drivers tend to ignore their speedometers.</div>
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This speed checker will come handy for the highway traffic police as it will not only provide a digital display in accordance with a vehicle’s speed but also sound an alarm if the vehicle exceeds the permissible speed for the highway.</div>
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The system basically comprises two laser transmitter-LDR sensor pairs, which are installed on the highway 100 metres apart, with the transmitter and the LDR sensor of each pair on the opposite sides of the road. The installation of lasers and LDRs is shown in Fig. 1. The system displays the time taken by the vehicle in crossing this 100m distance from one pair to the other with a resolution of 0.01 second, from which the speed of the vehicle can be calculated as follows:</div>
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<img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgnC69yIIQUNDwC1d1xwAFvwJiiTv97kRVi_vRrc1mDNq8arcrVhXm2rfeSJM9OmnDRhE2v4sFiPzRykC8p9ScqzdJvKHh4P_D-rx9qWMQfvZYLZy7NYdLYXwoc9SM1BIi107deKCdFa48I/s1600/Speed+Checker+for+Highways1.jpg" /></div>
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As per the above equation, for a speed of 40 kmph the display will read 900 (or 9 seconds), and for a speed of 60 kmph the display will read 600 (or 6 seconds). Note that the LSB of the display equals 0.01 second and each succeeding digit is ten times the preceding digit. You can similarly calculate the other readings (or time).</div>
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<img alt="Installation of lasers and LDRs" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgmkTasmi2-Jcs9jzmHBK-e_hvLQjZyQcjKDWJHRPiNSwLT63-ms-bl9eDAYDHQ9GdHFEF9sHt5PbWHyl40oqKMP0QuhQ5rPBnyTaCFAPKu009vSekXLisSHnLbqrKR5659btlpJQfVa9cO/s1600/Speed+Checker+for+Highways2.jpg" title="Installation of lasers and LDRs" /></div>
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<i><span style="color: red;">Fig. 1: Installation of lasers and LDRs on highway</span></i></div>
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<b>Circuit description</b></div>
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Fig. 2 shows the circuit of the speed checker. It has been designed assuming that the maximum permissible speed for highways is either 40 kmph or 60 kmph as per the traffic rule.</div>
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The circuit is built around five NE555 timer ICs (IC1 through IC5), four CD4026 counter ICs (IC6 through IC9) and four 7-segment displays (DIS1 through DIS4). IC1 through IC3 function as monostables, with IC1 serving as count-start mono, IC2 as count-stop mono and IC3 as speed-limit detector mono, controlled by IC1 and IC2 outputs. Bistable set-reset IC4 is also controlled by the outputs of IC1 and IC2 and it (IC4), in turn, controls switching on/off of the 100Hz (period = 0.01 second) astable timer IC5.</div>
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The time period of timer NE555 (IC1) count-start monostable multivibrator is adjusted using preset VR1 or VR2 and capacitor C1. For 40kmph limit the time period is set for 9 seconds using preset VR1, while for 60kmph limit the time period is set for 6 seconds using preset VR2. Slide switch S1 is used to select the time period as per the speed limit (40 kmph and 60 kmph, respectively). The junction of LDR1 and resistor R1 is coupled to pin 2 of IC1.</div>
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Normally, light from the laser keeps falling on the LDR sensor continuously and thus the LDR offers a low resistance and pin 2 of IC1 is high. Whenever light falling on the LDR is interrupted by any vehicle, the LDR resistance goes high and hence pin 2 of IC1 goes low to trigger the monostable. As a result, output pin 3 goes high for the preset period (9 or 6 seconds) and LED1 glows to indicate it. Reset pin 4 is controlled by the output of NAND gate N3 at power-on or whenever reset switch S2 is pushed.</div>
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<img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1cxbRgmpTTVhunwQwRz9QBv8rGNREi9Q5b8Y3XQvOOQg-M2MRAKwDUIAvCdHEcFW3R1wrG4dtrv7mfaGxNoVUKjo0RU7dzlmi2JLvOKXGTZVZzbWfKSR46F4-3DO659r4evoaNwpWX_nT/s1600/Speed+Checker+for+Highways3.jpg" /></div>
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For IC2, the monostable is triggered in the same way as IC1 when the vehicle intersects the laser beam incident on LDR2 to generate a small pulse for stopping the count and for use in the speed detection. LED2 glows for the duration for which pin 3 of IC2 is high.</div>
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The outputs of IC1 and IC2 are fed to input pins 2 and 1 of NAND gate N1, respectively. When the outputs of IC1 and IC2 go high simultaneously (meaning that the vehicle has crossed the preset speed limit), output pin 3 of gate N1 goes low to trigger monostable timer IC3. The output of IC3 is used for driving piezobuzzer PZ1, which alerts the operator of speed-limit violation. Resistor R9 and capacitor C5 decide the time period for which the piezobuzzer sounds.</div>
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The output of IC1 triggers the bistable (IC4) through gate N2 at the leading edge of the count-start pulse. When pin 2 of IC4 goes low, the high output at its pin 3 enables astable clock generator IC5. Since the count-stop pulse output of IC2 is connected to pin 6 of IC4 via diode D1, it resets clock generator IC5.  IC5 can also be reset via diode D2 at power-on as well as when reset switch S2 is pressed.</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiLOXUfXwj1vvNYagxWW51Z6Ax1-J00WKadTZEGh7TwOxfN1jlK-643kXtEukGh4-LPyvjf-zkGXjSnyg3z6vmBzJEInrI9gu2j_xiSe31eHEuzK_LV7Yshkybksj1ihfyhgrWB7FU1KJB1/s1600/Speed+Checker+for+Highways4.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="Circuit of Speed Checker for Highway" border="0" height="416" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiLOXUfXwj1vvNYagxWW51Z6Ax1-J00WKadTZEGh7TwOxfN1jlK-643kXtEukGh4-LPyvjf-zkGXjSnyg3z6vmBzJEInrI9gu2j_xiSe31eHEuzK_LV7Yshkybksj1ihfyhgrWB7FU1KJB1/s640/Speed+Checker+for+Highways4.jpg" title="Circuit of Speed Checker for Highway" width="640" /></a></div>
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<i><span style="color: red;">Fig. 2: Circuit of speed checker for highway</span></i></div>
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IC5 is configured as an astable multivibrator whose time period is decided by preset VR3, resistor R12 and capacitor C10. Using preset VR1, the frequency of the astable multivibrator is set as 100 Hz. The output of IC5 is fed to clock pin 1 of decade counter/7-segment decoder IC6 CD4026.</div>
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IC CD4026 is a 5-stage Johnson decade counter and an output decoder that converts the Johnson code into a 7-segment decoded output for driving DIS1 display. The counter advances by one count at the positive clock signal transition.</div>
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The carry-out (Cout) signal from CD4026 provides one clock after every ten clock inputs to clock the succeeding decade counter in a multidecade counting chain. This is achieved by connecting pin 5 of each CD4026 to pin 1 of the next CD4026.</div>
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A high reset signal clears the decade counter to its zero count. Pressing switch S2 provides a reset signal to pin 15 of all CD4026 ICs and also IC1 and IC4. Capacitor C12 and resistor R14 generate the power-on-reset signal.</div>
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<img alt="Power Supply" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgCF4_6HegKOkf_AuP74JEa8hstIQKqdAc5qvjwaY9xeY65lMe1v8tK21VjVfemCIw_felM1XsKN7anU7o4UvaSgh27YTvBFh-CVgepKu3vdUPDx0hTTaU3w7GzFQgvETBtsPVH5BlOwOa1/s1600/Speed+Checker+for+Highways5.jpg" title="Power Supply" /></div>
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<i><span style="color: red;">Fig. 3: Power supply</span></i></div>
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The seven decoded outputs ‘a’ through ‘g’ of CD4026s illuminate the proper segment of the 7-segment displays (DIS1 through DIS4) used for representing the decimal digits ‘0’ through ‘9.’ Resistors R16 through R19 limit the current across DIS1 through DIS4, respectively.</div>
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Fig. 3 shows the circuit of the power supply. The AC mains is stepped down by transformer X1 to deliver the secondary output of 15 volts, 500 mA. The transformer output is rectified by a bridge rectifier comprising diodes D3 through D6, filtered by capacitor C14 and regulated by IC11 to provide regulated 12V supply. Capacitor C15 bypasses any ripple in the regulated output. Switch S3 is used as the ‘on’/‘off’ switch. In mobile application of the circuit, where mains 230V AC is not available, it is advisable to use an external 12V battery. For activating the lasers used in conjunction with LDR1 and LDR2, separate batteries may be used.</div>
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Speed Checker for Highways

Speed Checker for Highways

While driving on highways, motorists should not exceed the maximum speed limit permitted for their vehicle. However, accidents keep occurr...

555 Timer IC Circuits

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<b>555 Timer Circuits/Projects/Schematics</b></div>
<ol>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2015/05/speed-checker-for-highways-circuit.html">Speed Checker for Highways</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2015/05/linear-timer-for-general-use-circuit.html">Linear Timer for General Use</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2015/05/water-pump-controller-circuit.html">Water Pump Controller</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2015/04/1-to-100-seconds-timer.html">1 to 100 Seconds Timer</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2015/03/led-chaser-circuit-using-cd4017-and.html">LED Chaser Circuit using CD4017 and NE555 Timer</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2015/03/light-alarm-with-timer-555.html">Light Alarm with Timer 555</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/11/voltage-doubler-circuit-using-ne555.html">Voltage Doubler Circuit using NE555</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/11/flasher-circuit-using-555-timer.html">Flasher Circuit using 555 Timer</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/11/police-siren-using-ne555.html">POLICE SIREN USING NE555</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/11/remote-controlled-switch-circuit.html">Remote Controlled Switch Circuit</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/11/sensitive-optical-burglar-alarm.html">Sensitive Optical Burglar Alarm</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/11/fridge-door-alarm-circuit.html">Fridge Door Alarm Circuit</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/11/1.5V-led-driver-circuit.html">1.5 V LED Driver Circuit</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/06/fire-alarm-circuit.html">Fire Alarm Circuit</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/05/switch-debouncing-circuit.html">Switch Debouncing Circuit</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/05/sensitive-intruder-alarm-circuit.html">Sensitive Intruder Alarm Circuit</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/05/seven-segment-intruder-alarm-circuit.html">Seven Segment Intruder Alarm Circuit</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2014/05/photo-switch-circuit-using-555-timer.html">Photo Switch Circuit using 555 Timer</a></li>
<li style="text-align: justify;"><a href="http://www.ecestream.com/2015/03/simple-dc-motor-pwm-speed-control-circuit.html">Simple DC motor PWM speed control</a></li>
</ol>
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<b>555 Timer Tutorials</b></div>
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<ol>
<li><a href="http://www.ecestream.com/2014/11/the-555-timer.html">The 555 Timer</a></li>
<li><a href="http://www.ecestream.com/2014/12/the-555-as-monostable-multivibrator.html">The 555 as a Monostable Multivibrator</a></li>
<li><a href="http://www.ecestream.com/2014/12/the-555-as-astable-multivibrator.html">The 555 as an Astable Multivibrator</a></li>
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<img alt="555 Timer" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxlnCh42aMnLKHWblaAt37LoDB7I68ixr6KfR420O1H30GMvsngtEvRZHv7uZfexNL4vRdURM5FtfI4GeS2eVs3haMII5sjeWqtZgt2X2QDbF4yvrZvCt5vXK29kF500LPDhBRGsluWL9d/s1600/555+timer.jpg" title="555 Timer" /></div>
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555 Timer IC Circuits

555 Timer IC Circuits

555 Timer Circuits/Projects/Schematics Speed Checker for Highways Linear Timer for General Use Water Pump Controller 1 to 100 Seco...

1 to 100 Seconds Timer

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This project is a timer project and build around popular 555 Timer IC, It can be used for all application required a delay of up to 100 Seconds. Onboard board preset to adjust the required timer duration in range of   of 1 to 100 Seconds, Tact switch SW1 to reset the timer and SW2 to start the timer. LED D3 works as power indicator and LED D2 to indicate timer operation.</div>
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Load can be connected to CN1 Screw Terminal, Out-put has both the operation normally Open and normally closed. Circuits works on 12V DC and consume approx. 100mA current. Very useful project can be used in various applications like water irrigation system, Kitchen timer etc.</div>
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Supply input 12 VDC @ 100 mA  </div>
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Onboard start and reset tactile switch  </div>
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Relay output: SPDT relay  </div>
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Relay specification: 5 A @ 250 VAC  </div>
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Relay state LED indicator  </div>
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Preset adjustable range function  </div>
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Power-On LED indicator  </div>
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Screw terminal connector for easy relay output connection  </div>
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Four mounting holes of 3.2 mm each  </div>
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PCB dimensions 48 mm x 63 mm</div>
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<b>Schematics</b></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7MLGpqQEfwn_GdrE5cHEdhSjqxPXssk1iH-MXp7Y_cbdbNrIgtWcVORDH6PvlV0b2mngrkm0Cgon7sb5c1-kgKfJZF8jdr_hA5BOREOJTDNVNOSnn7OLp77Jsjvwr1d7H-UK0YQcPA2L6/s1600/1_Sec_to_100_Seconds_Timer.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="414" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7MLGpqQEfwn_GdrE5cHEdhSjqxPXssk1iH-MXp7Y_cbdbNrIgtWcVORDH6PvlV0b2mngrkm0Cgon7sb5c1-kgKfJZF8jdr_hA5BOREOJTDNVNOSnn7OLp77Jsjvwr1d7H-UK0YQcPA2L6/s1600/1_Sec_to_100_Seconds_Timer.png" width="640" /></a></div>
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<b>Parts List</b></div>
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<img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiDmKffi_UNx1nDUq3weif8liTzYwiX9T1snc043yqumFCZLNo1A82ktvdOopUmhhsR11CELyYvU3RKuCF2nSIjBOxJvAA0GoBVsDyZwYiisEblO94B_ZwdNG84PHjrqDS9bKcB_-wH7EXj/s1600/1_Sec_to_100_Seconds_Timer_bom&top.png" /></div>
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1 to 100 Seconds Timer

1 to 100 Seconds Timer

This project is a timer project and build around popular 555 Timer IC, It can be used for all application required a delay of up to 100 Se...

Simple DC motor PWM speed control

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The 555 is ubiquitous and can be used as simple PWM speed control.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOyzt4bzBu6vU3oZIBq3gcIKawUm6-nXrhhMTyGFDs2Mdr6EnWTJpG8FqrEKXRjdkRyaPvWb4s6ClxX0Lz_cevxBKGwue9t_RnnLa9Ch1PezbnrA8Gzp3zCbdNmWEgkxXdt5PUzL3g1NNv/s1600/Simple+DC+motor+PWM+speed+control.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="Simple DC motor PWM speed control circuit" border="0" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOyzt4bzBu6vU3oZIBq3gcIKawUm6-nXrhhMTyGFDs2Mdr6EnWTJpG8FqrEKXRjdkRyaPvWb4s6ClxX0Lz_cevxBKGwue9t_RnnLa9Ch1PezbnrA8Gzp3zCbdNmWEgkxXdt5PUzL3g1NNv/s1600/Simple+DC+motor+PWM+speed+control.png" title="Simple DC motor PWM speed control" width="400" /></a></div>
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<strong><span style="color: #3d85c6;">Circuit Explanation:</span></strong><br />
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The 555 IC is wired as an astable and the frequency is constant and independent of the duty cycle, as the total resistance (R charge + R discharge, notice the diode) is constant and equal to 22Kohm (givin a frequency of about 1Khz, notice the hum).<br />
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When the potentiomenter is all up, the Rcharge resistance is 1,0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1,0 Kohm resistor) , and Rdischarge is 21 Kohm, giving a 5% on duty cycle and a 1Khz frequency.<br />
<br />
When the potentiomenter is all down, the Rcharge resistance is 21,0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1,0 Kohm resistor) , and Rdischarge is 1 Kohm, giving a 95% on duty cycle and a 1Khz frequency.<br />
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When the potentiomenter is at 50% , the Rcharge resistance is 11,0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1,0 Kohm resistor) , and R discharge is 11 Kohm, giving a 50% on duty cycle and a 1Khz frequency.<br />
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The 555 provide good current capability to drive the mosfet fast and to drive a bipolar transistor.<br />
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I actually use this system to drive the DC motor of my small Rotary spark gap Tesla coil at variable speed<br />
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If you are disgusted by the 1Khz hum of the motor try to rise the frequency out of the audible range (replacing the potenziometer), but rembember that at higher frequency inductive reactance of motor rises so the the efficiency would drop.<br />
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<strong><span style="color: #3d85c6;">Important:</span></strong><br />
<br />
Obviously the mosfet (or bipolar) must have enough current capability to drive the motor, so the drain (or collector) current must be equal to maximum motor current (at power supply voltage, when it is blocked). The snubber diode too, because it shorts the motor on the off cycle. Both mosfet (or bipolar) and diode have to be hooked to a heatsink if the max motor current is more than 100 or 200mA. Do not stress to much the motor with too much work because it overheats both motor, transistor and diode.<br />
<br />
If you don't want braking in the off cycle just place a resistor in series with the snubber diode, it  should rise a bit efficiency but have more inertia when slowing the motor down. The value of the resistor must be R=V (breakdown transistor) / Imax, and the power should be 5W. Mosfets have internal zener diode, but don't count on it.</div>
</div>

Simple DC motor PWM speed control

Simple DC motor PWM speed control

The 555 is ubiquitous and can be used as simple PWM speed control. Circuit Explanation: The 555 IC is wired as an astable and the f...

LED Chaser Circuit using CD4017 and NE555 Timer

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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg92ljnBPTQxdItXL2JaPGs2Yuf1j-mDjr321DCN62MJ_knQsmWLv6ROx7m9JKFyQvHuAPeoRWDouqrxC2yQo4OHMZZd1JyMkWlJvvonI8SqATqJ5YvhRTPnxAiYh2D54F39p8nkM7nx3IW/s1600/Led+Chaser+Circuit.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="LED-Chaser-Circuit-ecestream" border="0" height="304" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg92ljnBPTQxdItXL2JaPGs2Yuf1j-mDjr321DCN62MJ_knQsmWLv6ROx7m9JKFyQvHuAPeoRWDouqrxC2yQo4OHMZZd1JyMkWlJvvonI8SqATqJ5YvhRTPnxAiYh2D54F39p8nkM7nx3IW/s1600/Led+Chaser+Circuit.jpg" title="LED Chaser Circuit" width="320" /></a></div>
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You can build simple <a href="http://www.ecestream.com/2014/11/light-emitting-diodes-leds.html" target="_blank">LED</a> chaser circuits using CD4017 and NE555 timer. There are hundreds of projects in the internet for making such simple LED chaser circuits.</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiAO1ixtqFOWO-LHC_lKYv8h7HKzYxqzwgP5UZLZdl71Q-EChJTjFWoendtzIkDdDrvlsKBhwl7jHV5BwzAXDD3_0iC8WHthsNfaSAEx3cLYrmGkDkwLnoi51unLViKNNDv8M8NfMc_MwFI/s1600/Led+Chaser+Circuit+Diagram.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="LED-Chaser-Circuit-ecestream" border="0" height="331" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiAO1ixtqFOWO-LHC_lKYv8h7HKzYxqzwgP5UZLZdl71Q-EChJTjFWoendtzIkDdDrvlsKBhwl7jHV5BwzAXDD3_0iC8WHthsNfaSAEx3cLYrmGkDkwLnoi51unLViKNNDv8M8NfMc_MwFI/s1600/Led+Chaser+Circuit+Diagram.jpg" title="LED Chaser Circuit using CD4017 and NE555 Timer" width="400" /></a></div>
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This is the schematic for a very basic 10 LED chaser circuit. It used a 10 uF <a href="http://www.ecestream.com/2014/11/capacitor.html" target="_blank">capacitor</a> for C1. The 10K pot can reduce the flash speed from not moving to whatever minimum time constant is possible with the C1 value you choose. Don’t bother with ultra-bright LEDs for these “chaser” projects as cheaper, lower millicandela (mcd) LEDS work fine. I favor blue and green LEDS. The 4017 decade counter is a fabulous part and can be driven to flash a row of <a href="http://www.ecestream.com/2014/11/light-emitting-diodes-leds.html" target="_blank">LEDs</a> with a <a href="http://www.ecestream.com/2014/11/the-555-timer.html" target="_blank">555 timer</a> chip or a discrete <a href="http://www.ecestream.com/2014/12/bipolar-junction-transistors-bjts.html" target="_blank">BJT</a> multivibrator.</div>
</div>

LED Chaser Circuit using CD4017 and NE555 Timer

LED Chaser Circuit using CD4017 and NE555 Timer

You can build simple LED chaser circuits using CD4017 and NE555 timer. There are hundreds of projects in the internet for making such...

Light Alarm with Timer 555

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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjQiVVnZHb7XDIZB9zwEf3vdIDAGG0oWNxrAejc6j3bWPBsg4eCX3cmo0BfpRzL0zCEfB7Dh8cfyNJ5OwXV_VvthzWg7KcSWSPHPyeebxcwLkTmBFzP7vLilDtXaoV00hP-oB8JZTgx730f/s1600/Light-Alarm-Circuit-with-Timer-555.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="Light Alarm Circuit-ecestream" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjQiVVnZHb7XDIZB9zwEf3vdIDAGG0oWNxrAejc6j3bWPBsg4eCX3cmo0BfpRzL0zCEfB7Dh8cfyNJ5OwXV_VvthzWg7KcSWSPHPyeebxcwLkTmBFzP7vLilDtXaoV00hP-oB8JZTgx730f/s1600/Light-Alarm-Circuit-with-Timer-555.jpg" title="Light Alarm Circuit" /></a></div>
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<b><i>Figure: Light Alarm Circuit</i></b></div>
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This is the simple and low cost light alarm circuit built using timer IC <a href="http://www.ecestream.com/2014/11/the-555-timer.html" target="_blank">555</a> as the sound generator and a LDR to sense the environment light. This alarm is activated when the light beam on the LDR photocell is interrupted (You can use the light of a flashlight bulb which will make you a source for remain on, this may be 3 volts, no matter whether AC or DC).</div>
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<b>Components List:</b></div>
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<b><i>Capacitor:</i></b></div>
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C1: 0.1 μF</div>
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<b><i>Resistor:</i></b></div>
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R1: 100K (potensiometer)</div>
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R2: 1K</div>
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R3: 47K</div>
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R4: 100K</div>
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R5. 27 ohm</div>
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R6: 220 ohm</div>
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<b><i>Semiconductor:</i></b></div>
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IC1: 555</div>
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TR1: 2N3055, C1060 or C1226</div>
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D1: 1N4002</div>
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<b><i>Others:</i></b></div>
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Speaker 8 or 16 ohms</div>
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1 LDR / photocell</div>
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When the LDR / photocell is receiving light, has low resistance, thus blocking the positive voltage that gives R4 to terminal 4 of IC 555, maintaining multivibrator off and the speaker does not sound when the photocell stops receiving light, its resistance increases in fraction seconds, which makes it reaches the above positive voltage to the terminal, which activates the alarm.</div>
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<b>Note:</b> The LDR should not receive another light than that which serves to activated.</div>
</div>

Light Alarm with Timer 555

Light Alarm with Timer 555

Figure: Light Alarm Circuit This is the simple and low cost light alarm circuit built using timer IC 555 as the sound generator and...

Voltage Doubler Circuit using NE555

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The circuit diagram of a very simple <i><b>voltage doubler using NE555 timer</b></i> is shown here. Here IC NE555 is wired as an astable mutivibrator operating at around 9KHz. The base of the two transistors (Q1 and Q2) is shorted and output of the astable multivibrator (pin 3) is connected to it. When the output of astable multivibrator is low, Q1 will be OFF and Q2 will be ON. The negative terminal of the capacitor C3 will be shorted to ground through T2 and it will be charged to the input supply voltage. When the output of the astable multi vibrator is high, transistor Q1 will be ON and transistor Q2 will be OFF. The capacitor C4 will be charged to the voltage across capacitor C3 plus the input supply voltage (that is double the input voltage). This is how the circuit works.</div>
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This voltage doubler circuit can deliver only up to 50mA output current and above that current limit the output voltage will be dramatically reduced. The actual output voltage will be around 19V for a 12V DC input and also the output voltage will be a bit unstable. Anyway, for low current applications this circuit is well enough.</div>
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<b>Circuit Diagram</b></div>
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<b>Important Points</b></div>
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<ul>
<li>The circuit can be assembled on a vero board.</li>
<li>The output current should not be allowed to exceed 70mA.</li>
<li>IC1 must be mounted on a holder.</li>
</ul>
</div>
</div>

Voltage Doubler Circuit using NE555

Voltage Doubler Circuit using NE555

The circuit diagram of a very simple voltage doubler using NE555 timer is shown here. Here IC NE555 is wired as an astable mutivibrator o...

Flasher Circuit using 555 Timer

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<b><i>Flashing circuits</i></b> are very interesting. They grab your attention and can be used in many applications. They consume very little energy and a single cell can last as long as 12 months. You can flash globes, LEDs and pulse all types of devices such as motors, solenoids and piezo diaphragms. In this discussion we will cover a number of interesting "oscillator circuits." They can be adapted for other applications - but to do this you have to know how they work. This is not easy as most of them are quite complex. In fact oscillator circuits are one of the most difficult circuits to understand. But if you read the text, everything will become clear.</div>
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<b>Circuit Description</b></div>
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This is the circuit diagram of lamp flasher operated from mains. By this you can flash up to 200 Watt lamps at rates determined by you. IC NE555 is wired as an astable multivibrator for producing the pulses for flashing the lamp. The flashing rate can be set by the value of resistors R2 & R3.</div>
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Diodes D1 & D2 provides a half wave rectified regulated supply for the IC. Transistor T1 is used to drive triac and triac BT136 for driving the load. Resistor R4 limits the base current of Q1.</div>
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<b>Flashing Circuit Diagram & Parts List</b></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhopCht5orUrZNobzRoEJTLXqckb0CD_dFQKrxptUl7KFrz16NbnJeHze4-KHUIhehBvrZnjqJa_O9E_Or2G55g89DvUykHP_GzRi6I59Ww_GaCUy5vxhoAuxu-ynG53VuzdBuwkXN_mk8T/s1600/Flasher+Circuit.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhopCht5orUrZNobzRoEJTLXqckb0CD_dFQKrxptUl7KFrz16NbnJeHze4-KHUIhehBvrZnjqJa_O9E_Or2G55g89DvUykHP_GzRi6I59Ww_GaCUy5vxhoAuxu-ynG53VuzdBuwkXN_mk8T/s1600/Flasher+Circuit.png" /></a></div>
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<b>Notes</b></div>
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<ol>
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>Connect a 100K pot instead of R2 if you need frequent changes in rate.</li>
<li>Many parts of the circuit are live with potential shock hazards. So please be careful.</li>
<li>As usual use an IC holder for mounting the IC.</li>
</ol>
</div>
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Flasher Circuit using 555 Timer

Flasher Circuit using 555 Timer

Flashing circuits are very interesting. They grab your attention and can be used in many applications. They consume very little energy an...

POLICE SIREN USING NE555

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<span style="font-family: inherit;">A lot of electronic circuits using <b><i>NE555 timer IC</i></b> are already published here and this is just another one. Here is the circuit diagram of a police siren based on NE55 timer IC. The circuit uses two NE555 timers ICs and each of them are wired as <i>astable multivibrators</i>. The circuit can be powered from anything between 6 to 15V DC and is fairly loud. By connecting an additional power amplifier at the output you can further increase the loudness.</span></div>
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<span style="font-family: inherit;"><br /></span>
<span style="font-family: inherit;">IC1 is wired as a slow astable multivibrator operating at around 20Hz @ 50% duty cycle and IC2 is wired as fast astable multivibrator operating at around 600Hz.The output of first astable mutivibrator is connected to the control voltage input (pin5) of IC2. This makes the output of IC2 modulated by the output frequency of IC1, giving a siren effect. In simple words, the output frequency of IC2 is controlled by the output of IC1.</span><br />
<span style="font-family: inherit;"><br /></span></div>
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</div>
<div style="text-align: left;">
<span style="font-family: inherit;"><b>Circuit Diagram</b></span></div>
<span style="font-family: inherit;"><br /></span>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwtI14wBzYW2mtHRVF-7GlpLLqMjacmY1TdQR0HTJVH64thkgX5O3JHoYeP7LSiDIG9xKkF0pzZyJ9Kh31ljI7wReIGSHS9PEWq66hWcaf4I85S6vqm6C8wYh0km4PMCXQ5umhHLxYOhhG/s1600/POLICE+SIREN+USING+NE555.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><span style="font-family: inherit;"><img border="0" height="342" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwtI14wBzYW2mtHRVF-7GlpLLqMjacmY1TdQR0HTJVH64thkgX5O3JHoYeP7LSiDIG9xKkF0pzZyJ9Kh31ljI7wReIGSHS9PEWq66hWcaf4I85S6vqm6C8wYh0km4PMCXQ5umhHLxYOhhG/s1600/POLICE+SIREN+USING+NE555.png" width="640" /></span></a></div>
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<span style="font-family: inherit;"><br /></span></div>
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<span style="font-family: inherit;"><b>Notes</b></span></div>
<div style="text-align: justify;">
</div>
<ul>
<li><span style="font-family: inherit;">The circuit can be assembled on a Perf board.</span></li>
<li><span style="font-family: inherit;">I used 12V DC for powering the circuit.</span></li>
<li><span style="font-family: inherit;">Instead of using two NE55 timer ICs, you can also use a single NE556 timer.</span></li>
<li><span style="font-family: inherit;">NE556 is nothing but two NE555 ICs in one package.</span></li>
<li><span style="font-family: inherit;">Refer the datasheets of NE555 and NE556 to have a clear idea.</span></li>
<li><span style="font-family: inherit;">Speaker can be a 64ohm, 500mW one.</span></li>
</ul>
</div>

POLICE SIREN USING NE555

POLICE SIREN USING NE555

A lot of electronic circuits using NE555 timer IC are already published here and this is just another one. Here is the circuit diagram of...

Remote Controlled Switch Circuit

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This is a versatile<i> remote controlled switch</i> that can ON or OFF any appliance connected to it using a TV remote. <i><b>IR remote sensor IC TSOP 1738</b></i> is used for receiving the signal. Normally when no signal is falling on IC3 the output of it will be high. This makes Q1 OFF. When a signal of 38 KHz from the TV remote falls on the IC3 its output goes low. This makes Q1 conduct and a negative pulse is obtained at pin 2 of IC 1 <b>NE 555</b>. Due to this IC1 wired as a monostable multivibrator produces a 4 Sec long high signal at its output. This high output is the clock for IC 2 which is wired as a flipflop and of , its two outputs pin 3 goes low and pin 2 goes high. The high output at pin 2 is amplified to drive the relay. For the next signal the outputs of IC2 toggles state.  Result, we get a relay toggling on each press on the remote. Any appliance connected to this circuit can be switched ON or OFF.</div>
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<b>Remote Controlled Switch Circuit Diagram with Parts List</b></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjoCbGPywbwsveu_-CkvmkvvB632LBiSMoygn5CH_jOC_g-Asj_mIjD_wXMFT5HSwPcFxdr7YdF6lYUXfd41ZpWPmD2tcjS3-L9akdS73FIddwrW7mdpx1TLI6YQwxG7jmduPLRbFlQRuf5/s1600/Remote+Controlled+circuit.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="355" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjoCbGPywbwsveu_-CkvmkvvB632LBiSMoygn5CH_jOC_g-Asj_mIjD_wXMFT5HSwPcFxdr7YdF6lYUXfd41ZpWPmD2tcjS3-L9akdS73FIddwrW7mdpx1TLI6YQwxG7jmduPLRbFlQRuf5/s1600/Remote+Controlled+circuit.png" width="640" /></a></div>
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<i>IC1, IC2 = NE 555 / Timer</i></div>
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<i>IC3 = TSOP 1738 / IR remote sensor</i></div>
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<i>Q1 = BC 158 / Transistor</i></div>
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<i>Q2 = SL 100 / Transistor</i></div>
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<i><br /></i></div>
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<b>Important Points</b></div>
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<ul>
<li>Before wiring the circuit make sure that the carrier frequency of the TV remote you have is 38 kHz. For that wire the sensor part only, point your remote to the TSOP1738 and press any switch. If output of TSOP1738 goes low then OK, your remote is of 38Khz type. Nothing to worry almost all TV remote are of this type.</li>
<li>You can use any switch of the remote because for any switch the code only changes, the carrier frequency remains same. We need this carrier frequency only.</li>
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>The appliance can be connected through NO or NC and C contacts of the relay.</li>
<li>Use a regulated 6V power supply for the circuit.</li>
</ul>
</div>
</div>

Remote Controlled Switch Circuit

Remote Controlled Switch Circuit

This is a versatile remote controlled switch that can ON or OFF any appliance connected to it using a TV remote. IR remote sensor IC TSO...

Sensitive Optical Burglar Alarm

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This optical burglar alarm uses two 555 timer ICs (IC1 and IC2). Both the ICs are wired as astable multivibrators. The first astable multivibrator built around IC1 produces low frequencies, while the second astable multivibrator built around IC2 produces audio frequencies. General-purpose Darlington photo-transistor T1 is used as the light sensor. To increase the sensitivity of the circuit, NPN transistor T2 is used.</div>
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Place phototransistor T1 where light falls on it continuously. Phototransistor T1 receives light to provide base voltage to transistor T2. As a result, transistor T2 conduct to keep reset pin 4 of IC1 at low level. This disables the first multivibrator (IC1) and hence the second multivibrator (IC2) also remains reset so the alarm (LS1) does not sound.</div>
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<b>Circuit Diagram</b></div>
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<b><br /></b></div>
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<img height="352" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjXpsTNj7wBRBzK1i3BYR0TfdEJy9bY4kaPleSPVPix1fgrEXMM_T0qnNpGvpbhp1wRBhDQ9gwN5hyphenhyphenBavZX4Mwb5-5aeo1g8y_oxQfCpUPE66ShqXrbhI9CS1mVxaZOxNjlHtQ-G_jIWP4s/s1600/SENSITIVE+OPTICAL+BURGLAR+ALARM.jpg" width="640" /></div>
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When light falling on Darlington phototransistor T1 is obstructed, transistor T2 stops conducting and reset pin 4 of IC1 goes high. This enables the first multivibrator (IC1) and hence also the second multivibrator (IC2). As a result, a beep tone is heard from speaker LS1. The beep rate can be varied by using preset VR1, while the output frequency of IC2 can be varied by using another preset VR2.</div>
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This circuit works off a simple 6V-12V DC power supply.</div>
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<b>Parts List</b></div>
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<ul>
<li><b>Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)</b></li>
</ul>
</div>
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<ol>
<li>R1, R5 = 1 KΩ</li>
<li>R2 = 100 KΩ</li>
<li>R3 = 4.7 KΩ</li>
<li>R4 = 10 KΩ</li>
<li>VR1 = 1 MΩ</li>
<li>VR2 = 100 KΩ</li>
</ol>
</div>
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<ul>
<li><b>Capacitors</b></li>
</ul>
</div>
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<ol>
<li>C1 = 1 µF/16V</li>
<li>C2 = 0.01 µF</li>
<li>C3 = 0.047 µF</li>
<li>C4 = 0.01 µF</li>
<li>C5 = 47 µF/25V</li>
</ol>
</div>
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<ul>
<li><b>Semiconductors</b></li>
</ul>
</div>
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<ol>
<li>IC1, IC2 = NE555</li>
<li>T1 = 2N5777 Photo Transistor</li>
<li>T2 = BC547</li>
<li>LED1 = RED LED</li>
</ol>
</div>
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<ul>
<li><b>Miscellaneous</b></li>
</ul>
</div>
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<ol>
<li>LS1 = 8Ω / 0.5W</li>
</ol>
</div>
</div>

Sensitive Optical Burglar Alarm

Sensitive Optical Burglar Alarm

This optical burglar alarm uses two 555 timer ICs (IC1 and IC2). Both the ICs are wired as astable multivibrators. The first astable multi...

Fridge Door Alarm Circuit

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This fridge door alarm is using a 3V battery supply should be placed (in a small box) in the fridge near the lamp or close to the opening. With the door closed the photo resistor R2 presents a high resistance (>200K) thus clamping IC1 by holding C1 fully charged across R1 and D1. When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance (<2K) stopping C1 charging current. Therefore IC1, wired as an astable multivibrator, starts oscillating at a very low frequency and after a period of about 24 sec. its output pin (#3) goes high, enabling IC2.</div>
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This chip is also wired as an astable multivibrator, driving the Piezo sounder intermittently at about 5 times per second. The alarm is activated for about 17 sec. then stopped for the same time period and the cycle repeats until the fridge door closes.</div>
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<b>Important Notes</b></div>
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<ol>
<li>Delay time can be varied changing C1 and/or R3 values.</li>
<li>Beeper repetition rate can be varied changing C2 and/or R4 values.</li>
<li>Stand-by current drawing: 150µA.</li>
<li>Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.</li>
<li>Do not put this device in the freezer.</li>
</ol>
</div>
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<b>Circuit Diagram</b></div>
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<b><br /></b></div>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgY-7iYgwlV4a4SqrGMq_bYrUD4m6GLEyfq5PLBoAqcNmcvqRJNCI2hQ4k-fTai8o8Raf8Hn-88PuWpT433fFIlYbwXxaCUQcOBrgvcc6ncX193ZRsmS5qI0G-UY3hKVOO0NpQ1QTwAsgWp/s1600/Fridge+Door+Alarm+Circuit.gif" /></div>
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<b>Components List</b></div>
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<ol>
<li>R1 = 10K 1/4W Resistor</li>
<li>R2 = Photoresistor (any type)</li>
<li>R3 = 2M2 1/4W Resistor</li>
<li>R4 = 1M 1/4W Resistor</li>
<li>C1 = 10µF 25V Electrolytic Capacitor</li>
<li>C2 = 100nF 63V Polyester Capacitor</li>
<li>D1 = 1N4148 75V 150mA Diode</li>
<li>IC1 = 7555 or TS555CN CMos Timer ICs</li>
<li>IC2 = 7555 or TS555CN CMos Timer ICs</li>
<li>BZ1 = Piezo sounder (incorporating 3KHz oscillator)</li>
<li>B1 = 3V Battery (2 x 1.5V AA, AAA or smaller type Cells in series)</li>
</ol>
</div>
</div>

Fridge Door Alarm Circuit

Fridge Door Alarm Circuit

This fridge door alarm is using a 3V battery supply should be placed (in a small box) in the fridge near the lamp or close to the opening....

1.5 V LED Driver Circuit

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This 1.5V 555 LED driver is more of a fun learning experiment than a practical circuit. While the TLC555 can indeed drive a 3V white LED using the inductive discharge technique, it typifies the kind of problems present in low voltage circuits. Two circuits are presented: Basic 555 LED Driver and Bootstrapped 555 LED Driver.</div>
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<b>Circuit function</b></div>
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When the output (pin 7) goes low, it charges L1 and when it turns off, the voltage developed by the inductor discharge easily causes the voltage across the LED to increase to its threshold voltage and subsequently flow through the LED.</div>
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<b>555 LED Driver Schematic</b></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2YQBMyT7IilkcFOWEyLyZkCpqQAyKc0s2vcyti4a3-RFpVe7zqgRXBDcslzS3y_0-7emwXIq1nRuW50ctP-hAcDRU5hkeVPT2tbk5Ihm0kX_bXHFX14ZsxCfi82Q992Rjjw7hHY7BggCb/s1600/1.5+volt+LED+driver.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="272" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2YQBMyT7IilkcFOWEyLyZkCpqQAyKc0s2vcyti4a3-RFpVe7zqgRXBDcslzS3y_0-7emwXIq1nRuW50ctP-hAcDRU5hkeVPT2tbk5Ihm0kX_bXHFX14ZsxCfi82Q992Rjjw7hHY7BggCb/s1600/1.5+volt+LED+driver.png" width="640" /></a></div>
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<b>Bootstrap mode</b></div>
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Note that operation of the toggle switch is necessary to shock the device into oscillation at marginally low voltages – otherwise, it cannot start. What happens is that when the switch closes, C2 charges through L1 and rings up double the incident input voltage – this is the effect of series resonance. Rectifier D2 and capacitor C2 then hold Vcc at a higher voltage level until oscillation commences and L1 starts repetitively firing the LED at 3V thus keeping C2 charged. This is a very interesting part of the experiment.</div>
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<b>Not all 555s are created equal</b></div>
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To make this LED driver circuit function, the 555 must operate well below the specified minimum Vcc. Also, the maximum voltage specification of the open collector output (pin 7, discharge function) is not specified in relation to Vcc (pin 8). The first TLC555 worked so poorly under these conditions that I decided not to use its data. The particular LM555 was selected because I knew that it functioned OK at very low voltages. So a word for the wise – whoever attempts to replicate any of this stuff, will need a bag of 555s.</div>
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<b>Results, Fig 1</b></div>
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Minimum voltage TLC555: 1.36V (some LED current as low as 1.0V – self-starting @ 1.0V)</div>
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Minimum voltage LM555: 2.30V (no LED current below this point – self-starting @ 2.3V)</div>
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<b>Results, Fig 2, bootstrap mode</b></div>
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Minimum voltage TLC555: 1.13V (some LED current as low as 0.56V, self-starting @ 1.1V)</div>
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Minimum voltage LM555: 1.78V (some LED current as low as 0.80V, self-starting @ 2.5V)</div>
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<br /></div>
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<b>Datasheet ZXSC380 </b></div>
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Minimum startup and operating voltage: 0.9V typical, 1.0V max</div>
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<b>Conclusions</b></div>
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<br /></div>
<div style="text-align: justify;">
While the TLC555 can be made to work (sometimes and after a fashion), the ZXSC380 is a better choice having been designed specifically for this application. However, the ZXSC380 is available only in the tiny SO-23 package – not experimenter friendly – check out the SO-23 to protoboard adapter photo. Problems include poor low voltage operation and poor starting at low voltages. The selected TLC555 worked great at 1.5V, but poorly at 1.2V (Ni-Mh battery voltage).</div>
</div>

1.5 V LED Driver Circuit

1.5 V LED Driver Circuit

This 1.5V 555 LED driver is more of a fun learning experiment than a practical circuit. While the TLC555 can indeed drive a 3V white LED u...

Fire Alarm Circuit

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It will detect the fire automatically and inform to the people with an alarm. Now-a-days, fire alarms are must for the apartments, theaters, hotels, restaurants, coal mines, petrol bunks or gas stations, etc.Here is the simple fire alarm circuits which will use different concepts and different components for generating the fire alarm. The main basic concept is almost same that sensing the fire or heat by the component and giving that information to the remaining circuit to give alarm.</div>
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This is a simple fire alarm circuit using Germanium Diode and 555 timer. In this circuit Germanium Diode play very important role in detecting the fire.This circuit is very easy to construct, cost effective and implementable.</div>
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<b>Circuit Description</b></div>
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Here is the simple fire alarm circuit which costs less than 100 rupees. The key component in the circuit is DR25 (germanium diode) whose resistance will decrease with increase in temperature. The conduction of germanium diode will start at 70 degrees. So we may use germanium diode as a heat sensor. When the temperature is more than 70 degree, the germanium diode will conduct and trigger the NE555 timer through a transistor. The NE555 is configured in astable multivibrator and make the buzzer to alarm when germanium diode conducts. So that we can get alert and act according to the alarm.</div>
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<br /></div>
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<b>Circuit Diagram</b></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjI_LJKhDHQzsNioR4V7CUTIibzgGOih7ln8d1THy__bMIlYF3TD17LfLt_43Z5VeWevfrVyB0RQO_17EKAFpz9ZyNlLkQLjRtIoN7QixdkHGIEJGoxOmem-9tviu0PB0DQaNj_mHDZV4E4/s1600/Fire-Alarm-Circuit-Using-Germanium-Diode.jpg"><img border="0" height="309" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjI_LJKhDHQzsNioR4V7CUTIibzgGOih7ln8d1THy__bMIlYF3TD17LfLt_43Z5VeWevfrVyB0RQO_17EKAFpz9ZyNlLkQLjRtIoN7QixdkHGIEJGoxOmem-9tviu0PB0DQaNj_mHDZV4E4/s1600/Fire-Alarm-Circuit-Using-Germanium-Diode.jpg" width="640" /></a></div>
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<b>Circuit Explanation</b></div>
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The DR25 germanium diode is heat sensor which will conduct when temperature is increased at certain point. The DR25 is made reverse biased in the circuit. It will conduct only when it is more than 70degree of room temperature. </div>
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The DR25 is connected to the transistor in reverse bias, which has high reverse resistance (more than 10K ohm) and  does not make the transistor to turn off which is connected to the reset pin of 555 timer. The reset pin of 555timer will be in ground level when the transistor is turned off. Here, the 555 timer is configured as astable multivibrator. </div>
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When more than 70 degrees in room temperature occurred, the resistance of DR25 diode drops to 1k ohm which will make the transistor to turn off and make the reset pin to go high. This will generate the output at pin3 and make the sound through the alarm. </div>
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We can use 3 or more diodes in reverse bias connected in parallel and placed in different room. If there is fire accident, it will sense and make the alarm. </div>
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<b><i>Note</i></b></div>
<div style="text-align: justify;">
<ol>
<li>If DR25 germanium diode is available, you can still use AC128, AC188 or 2N360 germanium transistors. Use base and emitter junctions in place of cathode and anode. </li>
<li>Diode must be connected to the circuit in reverse bias.</li>
</ol>
</div>
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<ul><span style="font-family: Verdana, sans-serif;">
</span></ul>
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</span></div>
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Fire Alarm Circuit

Fire Alarm Circuit

It will detect the fire automatically and inform to the people with an alarm. Now-a-days, fire alarms are must for the apartments, theater...

Switch Debouncing Circuit

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<span style="font-family: inherit;"><b><i>Switch debouncing</i></b> is one of those things you generally have to live with when playing with switches and digital circuits. If you want to input a manual switch signal into a digital circuit you'll need to debounce the signal so a single press doesn't appear like multiple presses. This circuit will remove the transient spikes and contact bounces from a non-latching push button switch.</span><br />
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</div>
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<span style="font-family: inherit;"><b>Circuit Diagram</b></span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2lcz551Ie75Hmp7_n_Tv7tkCo3Glq0fWNvLuDV0alN3GTKGflDJroaOG9DoobstVb-kV46Hg3-8TGes-gpCjG3iAatIafR-hPzGX8fCiDhJhR2QtBUlWIB6_XPjynTfVaWb-20xB4nF9S/s1600/SWITCH+DEBOUNCING+CIRCUIT.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><span style="font-family: inherit;"><img border="0" height="626" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2lcz551Ie75Hmp7_n_Tv7tkCo3Glq0fWNvLuDV0alN3GTKGflDJroaOG9DoobstVb-kV46Hg3-8TGes-gpCjG3iAatIafR-hPzGX8fCiDhJhR2QtBUlWIB6_XPjynTfVaWb-20xB4nF9S/s1600/SWITCH+DEBOUNCING+CIRCUIT.png" width="640" /></span></a></div>
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<span style="font-family: inherit;"><b>Notes</b></span></div>
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<span style="font-family: inherit;">Using a 555 timer as a monostable circuit, it is easy to build a good switch debouncer circuit. There are many circuits for SPDT debouncing, but not many for a normally open, push-to-make press button switch (PBS). The 555 monostable gives an output pulse of around 20 ms with component values shown. The formula for determining the output pulse is:</span></div>
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<span style="font-family: inherit;">Tout = 1.1 R1 C1</span></div>
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<span style="font-family: inherit;"><br /></span></div>
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<span style="font-family: inherit;">With the values in my circuit this equates to :</span></div>
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<span style="font-family: inherit;"><br /></span></div>
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<span style="font-family: inherit;">Tout = 1.1*1.8*</span>10<sup><span style="font-family: inherit; font-size: 11pt; line-height: 16.8666667938232px;">6</span></sup><span style="font-family: inherit;">*10*10</span><sup><span style="font-size: 11pt; line-height: 115%;"><span style="font-family: inherit;">-9</span></span></sup><span style="font-family: inherit;"> = 0.0198 sec or 19.8 ms</span></div>
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<span style="font-family: inherit;">The 555 circuit can be re-triggered if the input is held low longer than the output pulse. To prevent this happening, I have included a further timing circuit comprised of the 1Meg resistor and 47n capacitor. Normally, the 47n capacitor is discharged via the 1 Meg resistor. When the switch is pressed the capacitor quickly charges and provides a brief negative pulse to the 555 input. When the capacitor is fully charged, the potential across the voltage divider formed by the 10k and 1Meg resistors is insufficient to retrigger the monostable. Releasing the switch quickly discharges the capacitor. The output of a 555 monostable is suitable for connecting to TTL and CMOS logic circuits.</span></div>
</div>

Switch Debouncing Circuit

Switch Debouncing Circuit

Switch debouncing is one of those things you generally have to live with when playing with switches and digital circuits. If you want to ...

Sensitive Intruder Alarm Circuit

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<span style="font-family: inherit;">This circuit diagram of an ultra sensitive intruder alarm. The shadow of an intruder passing few meters nearby the circuit is enough to trigger the alarm. Here IC2 uA 741 is wired as a sensitive comparator ,whose set point is set by R6 &R7. The voltage divide by LDR and R9 is given at non inverting pin of IC2. At standby mode these two voltages are set equal by adjusting R9. Now the output (pin6) of comparator will be high.Transistor Q1 will be off. The voltage at trigger pin of IC1 will be positive and there will be no alarm. When there is an intruder near the LDR the shadow causes its resistance to increase. Now the voltages at the inputs of comparator will be different and the out put of IC2 will be low. This makes Q1 on. This makes a negative going pulse to trigger the IC1 which is wired as a monostable multivibrator.The out put of IC1 will be amplified by Q2 (SL 100) to produce alarm.</span></div>
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<span style="font-family: inherit;"><b>Intruder Alarm Circuit Diagram with Parts List</b></span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmZe1wniPji8zfvC9vqtjleE9LCJBaBYGj9ayQ48Ublvxg_U8EztgOujXnKwdS7DNjsSZmiqTx-UiejMPV4wXGZpZJsTVHs2H_55fl4BF3Uy2wbK-rIhOuP2IRuDtnomk-ANSmwE3WH36w/s1600/Sensitive+Intruder+Alarm+Circuit.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><span style="font-family: inherit;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmZe1wniPji8zfvC9vqtjleE9LCJBaBYGj9ayQ48Ublvxg_U8EztgOujXnKwdS7DNjsSZmiqTx-UiejMPV4wXGZpZJsTVHs2H_55fl4BF3Uy2wbK-rIhOuP2IRuDtnomk-ANSmwE3WH36w/s1600/Sensitive+Intruder+Alarm+Circuit.jpg" /></span></a></div>
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<span style="font-family: inherit;"><b>Notes</b></span></div>
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<li><span style="font-family: inherit;">To setup the alarm ,power up the circuit and adjust R9 so that LED  D1 goes off.</span></li>
<li><span style="font-family: inherit;">The LDR can be housed in a dark tube to increase sensitivity.</span></li>
<li><span style="font-family: inherit;">The sensitivity is very important here. If you cannot adjust the required sensitivity properly, use one LOW resistance (~1K ) POT in series with  R9 for fine adjustment.</span></li>
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Sensitive Intruder Alarm Circuit

Sensitive Intruder Alarm Circuit

This circuit diagram of an ultra sensitive intruder alarm. The shadow of an intruder passing few meters nearby the circuit is enough to tr...

Seven Segment Intruder Alarm Circuit

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<span style="font-family: inherit;">Here is the circuit diagram of a seven segment counter based on the <i>counter IC CD 4033</i>. This circuit can be used in conjunction with various circuits where a counter to display the progress  adds some more attraction.<i> </i></span><span style="font-family: inherit;"><i>IC NE 555</i> is wired as an astable multivibrator for triggering the <i>CD 4033</i>. For each pulse the output of CD 4033 advances by one count.The output of CD 4033 is displayed by the seven segment <i>LED display LT543</i>. Switch S1 is used to initiate the counting. Diode D1 prevents the risk of accidental polarity reversal.</span></div>
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<span style="font-family: inherit;"><b>Seven Segment Circuit Diagram with Parts List</b></span></div>
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<span style="font-family: inherit; margin-left: 1em; margin-right: 1em; text-align: center;"><img alt="Seven Segment Intruder Alarm Circuit" border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYiwuaLI1Qc0n2HxXDbMjD0k7wZrmPq7oKW668T92FALtxr2TcrdSxR_0UT_OUETwwv3hYg7TAOEY5XfijzV0wgqH7yoWtCeQK3AEnPynk58aDN3B2n-kDQYcKqF8PLmJPIDGtMDVwul0W/s1600/Seven+Segment+Counter+Display+Circuit.jpg" title="Seven Segment Intruder Alarm Circuit" /></span></div>
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Seven Segment Intruder Alarm Circuit

Seven Segment Intruder Alarm Circuit

Here is the circuit diagram of a seven segment counter based on the counter IC CD 4033 . This circuit can be used in conjunction with vari...

Photo Switch Circuit using 555 Timer

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<span style="font-family: inherit;">This is a <b><i>simple photo switch</i></b> suitable for home and industrial purpose. The circuit switches on a relay when the light intensity falling on the sensor crosses the set limit.The circuit is based on a NE 555 and two transistors for driving the relay. The resistor R1 is adjusted such a way that under normal condition the voltage across the <b>LDR</b> is less than 1/3 the supply voltage. In this condition output of IC is high .This makes transistor Q1 on. Transistor Q2′s base is connected to collector of Q1. So Q2 will be off keeping the relay de energized. When light falls the voltage across LDR rises above 2/3 Vcc. This makes the output of IC go high making the relay to energized. The result we get a relay that operates according to the intensity of light falling on the LDR.</span><br />
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<span style="font-family: inherit;"><b>Circuit Diagram and Parts List</b></span></div>
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<span style="font-family: inherit; margin-left: 1em; margin-right: 1em;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhK5_JBrEHCMcEoYDsbNWq0jTY0W6zu7kyu8WzeaCbUVdUUZ_ry99b_QeOvQFjOXaoUjcMjM4AXm6r-a4C3mzp-vDQeeW4pv5_tngv_DTCiMuN8_ghT8whiX8m86uNh-vm8OZTKeq9dCZ7A/s1600/PHOTO+SWITCH+CIRCUIT+USING+NE+555.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="446" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhK5_JBrEHCMcEoYDsbNWq0jTY0W6zu7kyu8WzeaCbUVdUUZ_ry99b_QeOvQFjOXaoUjcMjM4AXm6r-a4C3mzp-vDQeeW4pv5_tngv_DTCiMuN8_ghT8whiX8m86uNh-vm8OZTKeq9dCZ7A/s1600/PHOTO+SWITCH+CIRCUIT+USING+NE+555.jpg" width="640" /></a></span></div>
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<b style="font-family: inherit;">Important Points</b></div>
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<li><span style="font-family: inherit;">Assemble the circuit on a good quality PCB or common board.</span></li>
<li><span style="font-family: inherit;">To setup the circuit switch on power supply, connect a multimeter across LDR and adjust R1 so that voltage across LDR is just below 1/3 supply voltage. Ensure that relay is off in this condition. If not reduce voltage across LDR further more by adjusting R1 to make relay off.</span></li>
<li><span style="font-family: inherit;">Now cover the top of LDR using a black paper and see the relay gets activated. If not, make further adjustments with R1. Nothing to care after some trial and error you will get the correct set piont of R1 where the circuit works. This circuit  is nothing great, but some simple basics. I have tested this and got good results.</span></li>
<li><span style="font-family: inherit;">If there is some chattering in the relay, that may be because off the difference between the turning on and turning off voltages. This can be avoided by connecting a resistor whose value is equal to 1/2 the resistance of LDR at illuminated condition.</span></li>
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Photo Switch Circuit using 555 Timer

Photo Switch Circuit using 555 Timer

This is a simple photo switch suitable for home and industrial purpose. The circuit switches on a relay when the light intensity falling ...

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