Object counter using 8051 microcontroller.
This article is about a simple object counter/visitor counter using 8051 microcontroller . AT89S51 belonging to the 8051 family is the microcontroller used here. This circuit can count the number of objects passing across a line , number of persons passing through a gate/door and so on. The can be simply divided into two sections i.e. the sensor section and the display section.
The sensor part consists of a ultra bright led (with focus), and LDR, opamp LM324 and the associated passive components. The LED is placed on one side of the door and the LDR is placed on the other side so that the light from the LED falls directly on the LDR.As you know, the resistance of the LDR has an inverse relationship with the intensity of the light falling on it. The preset resistor R14 is so adjusted that the voltage across the LDR is below 1.5V when it is illuminated. This voltage (labelled A in the circuit diagram) is connected to the inverting input of the opamp which is wired as a comparator with reference voltage 1.5V (set using R15 and R16).Capacitor C1 is meant for bypassing noise or anything like that which may cause false triggering.Resistor R13 is meant to control the current through the LED.
When the light is falling on the LDR the voltage across it will be less than the reference voltage and so the output of the opamp remains high. When the light beam is interrupted, the voltage across the LDR goes above the reference voltage and so the opamp output goes low and it indicates a pass.
The output of the opamp is fed to the INTO (interrupt 0) pin of the microcontroller. The microcontroller is programmed to count the number of negative edge pulses received at the INT0 pin and displays it on the three digit seven segment display.
ORG 000H SJMP INIT ORG 003H // starting address of interrupt service routine (ISR) ACALL ISR // calls interrupt service routine RETI INIT: MOV P0,#00000000B MOV P3,#11111111B MOV P1,#00000000B MOV R6,#00000000B MOV DPTR,#LUT SETB IP.0 // sets highest priority for the interrupt INT0 SETB TCON.0 // interrupt generated by a falling edge signal at INT0 pin SETB IE.0 //enables the external interrupt SETB IE.7 //enables the global interrupt control MAIN: MOV A,R6
MOV B,#100D DIV AB ACALL DISPLAY SETB P1.0 ACALL DELAY ACALL DELAY MOV A,B MOV B,#10D DIV AB ACALL DISPLAY CLR P1.0 SETB P1.1 ACALL DELAY ACALL DELAY MOV A,B ACALL DISPLAY CLR P1.1 SETB P1.2 ACALL DELAY ACALL DELAY CLR P1.2 SJMP MAIN ISR: INC R6 //interrupt service routine RET DISPLAY: MOVC A,@A+DPTR // display sub routine CPL A MOV P0,A RET DELAY: MOV R3,#255D // 1mS delay LABEL: DJNZ R3,LABEL RET LUT: DB 3FH DB 06H DB 5BH DB 4FH DB 66H DB 6DH DB 7DH DB 07H DB 7FH DB 6FH END
About the program.
The program is written so that, it keeps displaying the current value in register R6 on the three digit seven segment display. When ever there is a valid negative going pulse (interrupt) at the INT0 pin, the program branches to the interrupt service routine (sub routine ISR). Subroutine ISR increments the value in register R6, then jumps back to the MAIN loop and the display gets updated by the new value.
Entire circuit can be powered from a 5V DC supply.
LDR must be placed in an enclosure so that the light from LED alone falls on it.