ECEstream: Converter Circuits

Digital to Analog Converter using Binary-Weighted Resistors ( R-2R )

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The R-2R ladder DAC which is a binary-weighted DAC that uses a repeating cascaded structure of resistor values R and 2R. This improves the precision due to the relative ease of producing equal valued-matched resistors (or current sources). However, wide converters perform slowly due to increasingly large RC-constants for each added R-2R link. The D/A converter using binary-weighted resistors is shown in the figure below. In the circuit, the op-amp is connected in the inverting mode. The op-amp can also be connected in the non-inverting mode. The circuit diagram represents a 4-digit converter. Thus, the number of binary inputs is four.</div>
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<b>Circuit Diagram</b></div>
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We know that, a 4-bit converter will have <span style="font-family: inherit;"><span style="font-size: 11pt; line-height: 16.8666667938232px; text-align: left;">2</span><sup style="line-height: 15.3333320617676px; text-align: left;">4</sup></span> = 16 combinations of output. Thus, a corresponding 16 outputs of analog will also be present for the binary inputs.</div>
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Four switches from b0 to b3 are available to simulate the binary inputs: in practice, a 4-bit binary counter such as a 7493 can also be used.</div>
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<b>Working</b></div>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjumAuTw9blngmDntyfZWgM9FA9B2m9SxivwlgGS4y6sCnVNjUz_beN0VSBX4JR_2mdOaM9iLfAZv26j7kTg5KMBAWbQmMvgIkaTCw8ES8_zFDPIJTjH1izKzOf1MvsTpJsoeWE7ZQ3Klle/s1600/Digital+to+Analog+Converter+using+Binary-Weighted+Resistors.jpg" /></div>
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The circuit is basically working as a current to voltage converter.</div>
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<b>1. b0 is closed</b></div>
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It will be connected directly  to the +5V.</div>
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Thus, voltage across R = 5V</div>
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Current through R = 5V/10kohm = 0.5mA</div>
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Current through feedback resistor, Rf = 0.5mA (Since, Input bias current, IB is negligible)</div>
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Thus, output voltage = -(1kohm)*(0.5mA) = -0.5V</div>
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<b>2. b1 is closed, b0 is open</b></div>
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R/2 will be connected to the positive supply of the +5V.</div>
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Current through R will become twice the value of current (1mA) to flow through Rf.</div>
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Thus, output voltage also doubles.</div>
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<b>3. b0 and b1 are closed</b></div>
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Current through Rf = 1.5mA</div>
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Output voltage = -(1kohm)*(1.5mA) = -1.5V</div>
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Thus, according to the position (ON/OFF) of the switches (bo-b3), the corresponding “binary-weighted” currents will be obtained in the input resistor. The current through Rf will be the sum of these currents. This overall current is then converted to its proportional output voltage. Naturally, the output will be maximum if the switches (b0-b3) are closed,</div>
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V0 = -Rf *([b0/R][b1/(R/2)][b2/(R/4)][b3/(R/8)]) </div>
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Where each of the inputs b3, b2, b1, and b0 may either be HIGH (+5V) or LOW (0V).</div>
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The graph with the analog outputs versus possible combinations of inputs is shown below.</div>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhuKf6HzX418NZB3HGZoILfxzBvuLQyN_hPHXT5VSy-BEcYrRH1WSrzS5pBPCL_SCrGKJOOcu3VF5UOGtqGUHYlR51SDE9gifPUHEFDFVH04bdydOJ4Oc_vWBGV6jm8t6B9YA63ldQKoDXb/s1600/Digital+to+Analog+Converter+using+Binary-Weighted+Resistors1.jpg" /></div>
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The output is a negative going staircase waveform with 15 steps of -).5V each. In practice, due to the variations in the logic HIGH voltage levels, all the steps will not have the same size. The value of the feedback resistor Rf changes the size of the steps. Thus, a desired size for a step can be obtained by connecting the appropriate feedback resistor. The only condition to look out for is that the maximum output voltage should not exceed the saturation levels of the op-amp. Metal-film resistors are more preferred for obtaining accurate outputs.</div>
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<b>Disadvantages</b></div>
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If the number of inputs (>4) or combinations (>16) is more, the binary-weighted resistors may not be readily available. This is why; R and 2R method is more preferred as it requires only two sets of precision resistance values.</div>
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Digital to Analog Converter using Binary-Weighted Resistors ( R-2R )

The R-2R ladder DAC which is a binary-weighted DAC that uses a repeating cascaded structure of resistor values R and 2R. This improves the...

Analog to Digital Converter (A/D)

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This type of converter is used to convert analog voltage to its corresponding digital output. The function of the analog to digital converter is exactly opposite to that of a DIGITAL TO ANALOG CONVERTER. Like a D/A converter, an A/D converter is also specified as 8, 10, 12 or 16 bit. Though there are many types of A/D converters, we will be discussing only about the successive approximation type.</div>
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<b>Successive Approximation Type Analog to Digital Converter</b></div>
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A successive approximation A/D converter consists of a comparator, a successive approximation register (SAR), output latches, and a D/A converter. The circuit diagram is shown below.</div>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi7mpo73bQbY34s2_FTm8TyPMug7VjFQD1UiIwc6yi5xNrakVjHpV3oF0tRqPdvQ67hZdV40IF1BS8UjVhlJ-naEPf3QADuvaJuVNMiiAoBgfNNEViYje1OyJJKZGdUDKALiaGQn156Hxpd/s1600/ANALOG+TO+DIGITAL+CONVERTER.jpg" /></div>
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The main part of the circuit is the 8-bit SAR, whose output is given to an 8-bit D/A converter. The analog output Va of the D/A converter is then compared to an analog signal Vin by the comparator. The output of the comparator is a serial data input to the SAR. Till the digital output (8 bits) of the SAR is equivalent to the analog input Vin, the SAR adjusts itself. The 8-bit latch at the end of conversation holds onto the resultant digital data output.</div>
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<b>Working</b></div>
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At the start of a conversion cycle, the SAR is reset by making the start signal (S) high. The MSB of the SAR (Q7) is set as soon as the first transition from LOW to HIGH is introduced. The output is given to the D/A converter which produces an analog equivalent of the MSB and is compared with the analog input Vin.</div>
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If comparator output is LOW, D/A output will be greater than Vin and the MSB will be cleared by the SAR. If comparator output is HIGH, D/A output will be less than Vin and the MSB will be set to the next position (Q7 to Q6) by the SAR.</div>
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According to the comparator output, the SAR will either keep or reset the Q6 bit. This process goes on until all the bits are tried. After Q0 is tried, the SAR makes the conversion complete (CC) signal HIGH to show that the parallel output lines contain valid data. The CC signal in turn enables the latch, and digital data appear at the output of the latch. As the SAR determines each bit, digital data is also available serially. As shown in the figure above, the CC signal is connected to the start conversion input in order to convert the cycle continuously.</div>
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The biggest advantage of such a circuit is its high speed. It may be more complex than an A/D converter, but it offers better resolution.</div>
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Analog to Digital Converter (A/D)

This type of converter is used to convert analog voltage to its corresponding digital output. The function of the analog to digital conver...

Frequency to Voltage Converter

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A very simple and low cost frequency to voltage converter based on the TC9400 IC from Microchip is shown here. TC9400 can be either wired as a voltage to frequency converter or frequency to voltage converter and it requires minimum external components. The functional blocks inside the TC9400 includes integrator opamp, 3uS delay circuit, one shot circuit, charge discharge control circuit, divide by 2 network and necessary drivers. This circuit finds application in a range of electronic projects like frequency meters, tachometers, speedometers, FM demodulators etc.</div>
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<b>Circuit Diagram</b></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh5L79IQIK2A6gZzK1NKaNJn-2T3HHLBzvCUm5ivwcqy7kR8yM4C7esO5UlO6up9R3yYONojgkeNwLVGqQ19bC6F1vygaFooGlR0Qnu0mKnRaPc6bhJS53gxozdOHxGjYn93HowvYPNr2_R/s1600/Frequency+to+voltage+converter.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh5L79IQIK2A6gZzK1NKaNJn-2T3HHLBzvCUm5ivwcqy7kR8yM4C7esO5UlO6up9R3yYONojgkeNwLVGqQ19bC6F1vygaFooGlR0Qnu0mKnRaPc6bhJS53gxozdOHxGjYn93HowvYPNr2_R/s1600/Frequency+to+voltage+converter.png" /></a></div>
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In the circuit shown above the TC9400 is wired as a F to V converter that operates from a single supply. The circuit generates an output voltage that is proportional to the input frequency. The input frequency is applied to the pin11 (non inverting input of the internal comparator). In order to trip the comparator the amplitude of the input frequency must be greater than +/-200mV.Below this level the circuit will not work at any situation.</div>
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Whenever the input signal to the pin 11 of IC1 crosses zero to the negative direction the output of the internal comparator goes low. The 3uS delay circuit enables the Cref charge/discharge circuit after 3uS and this connects the Cref to the reference voltage and this charges the integrating capacitor Cint a specific amount of voltage. In the single supply operation the reference voltage is the potential difference between pin 2 and 7 of the TC9400. Each time the input frequency wave form crosses zero towards positive direction, the output of the internal comparator goes high and this disables the Cref charge/discharge circuit which creates a short circuit across the Cref leads. The voltage across the integrating capacitor Cint is retained because the only discharge path available is the 1M resistor Rint which is a too high and the voltage across Cint is the output voltage. Resistor Rbiasis used to set the bias current of the IC.</div>
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The potential divider network comprising of R6 and R7 makes sure that the input threshold tracks the supply voltage always. The clamp circuit using diode D2 prevents the input from going far negative in order to turn on the internal comparator. In simple words this section of the circuit can be generally termed as a level shifter.</div>
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The TC9400 manufacturers claim that it can accept a signal of any frequency at its input. In the practical side, for the proper working of this circuit the positive half of the input signal must have at least 5uS pulse width and for the negative half it must be greater than or equal to 5uS.</div>
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For calibration adjust the offset adjust trimpot to obtain 0V at the output with no input frequency applied. If you have a function generator, set frequency input to 10KHz and make adjustments in the value of Cref to get around 2.5 to 3 volts at the output. This calibration is meant for a maximum input frequency of 10KHz.</div>
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<b>Important points to remember</b></div>
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<li>The circuit can be assembled on a Perfect board or PCB.</li>
<li>The circuit can be powered from anything between 10 to 15V DC.</li>
<li>R3 can be used for adjusting the offset voltage.</li>
<li>In the circuit the inverting input of the internal comparator is referenced to 6.2V by using D1. So the input signals amplitude must be between 4V and the supply voltage (V+).</li>
<li>The output voltage is also referenced to 6.2V in this circuit.</li>
<li>The output voltage and input frequency of the F to V converter is related using the equation V out = V ref x C ref x F in where V out is the output voltage and F in is the input frequency.</li>
<li>TC9400 and TL071  must be mounted on holders.</li>
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Frequency to Voltage Converter

A very simple and low cost frequency to voltage converter based on the TC9400 IC from Microchip is shown here. TC9400 can be either wired ...

Light to Frequency Converter

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This is the circuit diagram of a effective light to frequency converter circuit that can be used for variety of applications such as light intensity measurement,fun etc. This circuit is based on TLC555, the CMOS version of famous timer IC NE 555. A photo diode is used for sensing the light intensity. The timer IC is wired in astable mode. The leakage current of the reverse biased photo diode is proportional to the light intensity falling on it. This leakage current charges the capacitance C1. When the capacitor voltage reaches 2/3 of the supply voltage the out put (pin 3) goes low. As a result the capacitor discharges through photo diode .When the capacitor voltage reaches 1/3 the supply voltage the out put (pin 3) of IC goes high. This cycling continues and we get a frequency at pin 3  proportional to the light intensity falling on the photo diode.</div>
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<b>Light to Frequency Converter Circuit Diagram & Parts List</b></div>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiW0Qlp_iiqjvbp3510DN9qfEc0xi7hkTcZqSo8dBENdLh9MDoktTmJl-2GNErRXz0_Lu_Bi-4IOpPrpJX_A_cICCvm067XQLHmaEWb_fF3d0f_oyxw28-VMOCsbytjan5lAP3rpinp6TT9/s1600/LIGHT+TO+FREQUENCY+CONVERTER+CIRCUIT.jpg" /></div>
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<b>Points to remember</b></div>
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With the given components the frequency  varies from 1KHZ @ complete darkness to  24 Khz @  bright sunlight.The frequency range can be changed by using different values for C1.</div>
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Use any general purpose photo diode for D1.</div>
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Light to Frequency Converter

This is the circuit diagram of a effective light to frequency converter circuit that can be used for variety of applications such as light...

Speaker to Microphone Converter

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This circuit is a simple approach for converting a loud speaker into a microphone. When the sound waves fall on the diaphragm of a speaker, there will be fluctuations in the coil and there will be a small proportional induced voltage. Usually this induced voltage is very low in magnitude and useless. Here in the circuit the low voltage is amplified using transistors to produce a reasonable output. The transistor Q1 is wired in common base mode and produces the required voltage gain. The transistor Q2 is wired as an emitter follower to produce enough current gain. The voice quality of this circuit will not be as much as a conventional microphone but quite reasonable quality can be obtained. To set up the circuit, keep the preset R2 at around 10 Ohms and connect the battery. Now adjust R2 to obtain the optimum sound quality.</div>
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<b>Circuit Diagram with Parts list</b></div>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi2T2Gl4DpwzmyNU1-UQLbz9IiAUxUj9GYtPeL_6TWUEmhHGqxS4GF3guwW4N3SGUcZGSRTfDpbV9C3ExQbndZ5pvXl4F2sxyYvOeNIwMc9M4YGZLbUPF2s7hFHuweGfR3sfS6Cg8ZgmA_I/s1600/SPEAKER+TO+MICROPHONE+CONVERTER.jpg" /></div>
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<b>Notes</b></div>
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Assemble the circuit on a general purpose PCB.</div>
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Power the circuit from a 9 V PP3 battery.</div>
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A 3 inch speaker can be used as K1.</div>
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All capacitors must be rated at least 15V.</div>
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An 8 Ohm speaker or head phone can be connected at the output to hear the picked sound.</div>
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Speaker to Microphone Converter

This circuit is a simple approach for converting a loud speaker into a microphone. When the sound waves fall on the diaphragm of a speaker...

Converting CD-ROM Drive to Audio CD Player

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Here is the simplest scheme for converting a CD ROM drive of your computer to a Audio CD player. The minimum requirement for the player is that, it should have a audio output and skip button.The CD ROM drive needs two voltages, 12V & 5V for its operation. So the main objective is to build a suitable power supply for the CD ROM drive. The IC1 (7812) together with associated components produce a regulated 12V DC. The IC2 (7805) together with associated components produce a regulated 5V DC. These voltages as well as ground can be connected to the corresponding voltage pins of the CD ROM drive using a male type CD ROM drive power connector. The 12V can be connected to the yellow wire of connector, 5V to red wire and GND to black wire as shown in figure1. Now the power supply is ready.</div>
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<b>Testing</b></div>
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Make the circuit as shown in the circuit diagram. Power up the circuit after connecting the power connector to the CD ROM drive. Now the power LED of the drive will glow.Insert the audio CD. Now the music will be available at the audio output socket of the drive.It can be heard using a headphone. The skip button of the drive can be used to play next song.</div>
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By connecting the audio output to a power amplifier you can enjoy the music in a greater wattage.</div>
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<b>Circuit Diagram with Parts list</b></div>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhvy1vyJa4-n9WcwKYYBPz7p9h0_ZcHqZXWtyxNd-r794SYr1F3tfNVgC8RBicS8Q05GWvonURJXKp7gSolgeH2LC3jle7qNxitobR_SxZczr00xoI1LA0YHgNnpKTGzZIZFIRM52g-GsWp/s1600/CONVERTING+CD-ROM+DRIVE+TO+AUDIO+CD+PLAYER.jpg" /></div>
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<b>Notes</b></div>
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<li>For car stereo applications you don’t need the transformer,rectifier and the 7812 regulator. 12V will be available from battery.You just need to produce a 5V from it using a 7805 based regulator. Connect the corresponding voltages to the connector as shown in figure 1 and connect the connector to drive.Done.</li>
<li>The amplifier for the car audio CD player must be one operating from 12V.</li>
<li>Do not connect the voltages to CD ROM drive in wrong polarity.Double check the voltages using a multimeter. Wrong polarity could easily damage the drive.</li>
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<img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgYL06dz9Jq1ICZlaMZPillnqoi9WkTd3bICqNEwSzJTrlJXCIn7FqedSruH-jDFYrRa87ARxRoFUVDBAZ-nlS7IMgL1_XSFrYHBikW446sFjSN5nhEh0BwAIdlav2vVoyAVNrhD9gYO8mR/s1600/CONVERTING+CD-ROM+DRIVE+TO+AUDIO+CD+PLAYER2.jpg" /></div>
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Converting CD-ROM Drive to Audio CD Player

Here is the simplest scheme for converting a CD ROM drive of your computer to a Audio CD player. The minimum requirement for the player is...

ECEstream

Digital to Analog Converter using Binary-Weighted Resistors ( R-2R )

Analog to Digital Converter (A/D)

Frequency to Voltage Converter

Light to Frequency Converter

Speaker to Microphone Converter

Converting CD-ROM Drive to Audio CD Player

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