Water Level Controller using 8051

A water level controller based using 8051 is shown in this article. A lot of water level controller projects have been published in this website but the is the first one based on a microcontroller. This water level controller monitors the level of the overhead tank and automatically switches on the water pump whenever the level goes below a preset limit. The level of the overhead tank is indicated using 5 leds and the pump is switched of when the overhead tank is filled. The pump is not allowed to start if the water level in the sump tank is low and also the pump is switched off when the level inside the sump tank goes low during a pumping cycle. The circuit diagram of the water level controller is shown below.

The level sensor probes for the overhead tank are interfaced to the port 2 of the microcontroller through transistors. Have a look at the sensor probe arrangement for the overhead tank in Fig1. A positive voltage supply probe goes to the down bottom of the tank. The probes for sensing 1/4, 1/2, 3/4 and FULL levels are placed with equal spacing one by one above the bottom positive probe. Consider the topmost (full level) probe, its other end is connected to the base of transistor Q4 through resistor R16. Whenever water rises to the full level current flows into the base of transistor Q4 which makes it ON and so its collector voltage goes low. The collector of Q4 is connected to P2.4 and a low voltage at P2.4 means the overhead tank is not FULL. When water level goes below the full level probe, the base of Q2 becomes open making it OFF. Now its collector voltage goes high and high at P2.4 means the tank is not full. The same applies to other sensor probes (3/4, 1/2, 1/4) and the microprocessor understands the current level by scanning the port pins P2.4, P2.5, P2.6 and P2.7. All these port pin are high (all sensor probes are open) means the tank is empty.

Port pin P0.5 is used to control the pump. Whenever it is required start pumping, the controller makes P0.5 low which makes transistor Q6 ON which in turn activates the relay K1 that switches the pump. Also the LED d6 glows indicating the motor is ON. LED D7 is the low sump indicator. When the water level in the sump tank goes low, the controller makes P0.7 low which makes LED D7 to glow. The circuit diagram of the water level controller is shown in the figure below.

Circuit Diagram

Program

MOV P2,#11111111B // initiates P2 as sensor input

MOV P0,#11111111B // initiates P2 as the output port

MOV A,#00000000B

MAIN: ACALL SMPCK // checks the level of the sump tank

MOV A,P2 // moves the current status of P2 tp A

CJNE A,#11110000B,LABEL1 // checks whether tank is full

SETB P0.1

SETB P0.2

SETB P0.3

SETB P0.4

CLR P0.0 // glows full level LED

SETB P0.5

LABEL1: MOV A,P2

CJNE A,#11111000B,LABEL2 // checks whether tank is 3/4

SETB P0.0

SETB P0.2

SETB P0.3

SETB P0.4

CLR P0.1 // glows 3/4 level LED

LABEL2: MOV A,P2

CJNE A,#11111100B,LABEL3 // checks whether tank is 1/2

SETB P0.0

SETB P0.1

SETB P0.3

SETB P0.4

CLR P0.2 // glows 1/2 level LED

LABEL3: MOV A,P2

CJNE A,#11111110B,LABEL4 // checks whether tank is 1/4

SETB P0.0

SETB P0.1

SETB P0.2

SETB P0.4

CLR P0.3 // glows 1/4 level LED

JB P0.6,LABEL4

CLR P0.5 // switches motor ON

LABEL4: MOV A,P2

CJNE A,#11111111B,MAIN // checks whether tank is empty

SETB P0.0

SETB P0.1

SETB P0.2

SETB P0.3

CLR P0.4 // glows EMPTY LED

JB P0.6,MAIN // checks whether sump is low

CLR P0.5 // switches motor ON

SJMP MAIN

SMPCK: JB P0.6,LABEL5 // checks whether sump is low

SETB P0.7 // extinguishes the sump low indicator LED

SJMP LABEL6

LABEL5: SETB P0.5 // switches the pump OFF

CLR P0.7 // glows sump low indicator LED

LABEL6: RET

END