RANDOM TRAFFIC LIGHT FOR EMPLOYEE INSPECTION

At my job we had problems with someone stealing goods from the plant. Routine inspection cannot be performed on every car, since we would have a row of

unhappy drivers behind. So we borrowed the idea from the airports random inspection. I designed a simple system that would light a green (meaning no inspection subject)

or red (inspection subject). The probability is preprogrammed on a PIC16F84. There are two buttons: one for lamp test, and one for random generation.

Using two “truck” type plastic covers to give off the red and green light from normal 5 Watt 110 V bulbs.	I used a mobile (cell phone) charger to power up the PIC16F84. and arcade style press buttons.
Two relays switch the lamps.	Already mounted at the exit gate of the plant.

I decided to use a PIC since the circuit is very simple and everythinh is done in software. All is explained in the .ASM listing (commented in Spanish though):

; Semaforo de valor aleatorio. Probabilidad determinada

; por el status de un bit en un contador. Entre mayor peso,

; menor probabilidad.

; Tambien se cuenta con un boton para probar las lamparas

processor 16f84

include <p16f84.inc>

__config _XT_OSC & _WDT_OFF & _PWRTE_ON

; Variables genericas

d0 equ H'0C'

d1 equ H'0D'

d2 equ H'0E'

count equ H'0F'

filter equ H'10'

; Entradas

TEST equ H'00' ;Entrada para prueba de lamparas

PRESS equ H'01' ;Entrada para boton de semaforo

; Constantes

VALOR equ D'25' ;Determina probabilidad VALOR/255

; Salidas

ROJO equ H'02' ;Foco rojo

VERDE equ H'03' ;Foco verde

;Inicializacion

org 0 ;Inicia en direccion 0

bsf STATUS,RP0 ;Selecciona regs. Banco 1

movlw B'00000011' ;B0..B2 Entradas/B3..B7 Salidas

movwf TRISB

movlw B'11111111' ;A0..A4 como entradas

movwf TRISA

bcf STATUS,RP0 ;Selecciona regs. Banco 0

movlw B'00000000' ;Salidas apagadas

movwf PORTB

Lazo:

incf count,F

btfsc PORTB, TEST ;Entrada para probar lamparas

goto Lamp_Test

btfss PORTB, PRESS ;Entrada para desicion

goto Lazo

call D20ms

btfss PORTB, PRESS

goto Lazo

movlw VALOR

subwf count,W

btfsc STATUS,C ;Es el contador > VALOR?

bsf PORTB,VERDE

nop

btfss STATUS,C ;Es el contador < VALOR?

bsf PORTB,ROJO

nop

goto Delay

Lamp_Test:

bsf PORTB,VERDE

bsf PORTB,ROJO

Delay:

; Clock frequency = 4 Mhz

; Actual delay = 5 Seconds

; (5000000 Cycles)

movlw 0x6E

movwf d0

movlw 0x5E

movwf d1

movlw 0x1A

movwf d2

loop1:

decfsz d0, f

goto loop1

decfsz d1, f

goto loop1

decfsz d2, f

goto loop1

; Rest = 1 Cycles

nop

; Apaga las lamparas

bcf PORTB,VERDE

bcf PORTB,ROJO

; Clock frequency = 4 Mhz

; Actual delay = .5 Seconds

; (500000 Cycles)

movlw 0x55

movwf d0

movlw 0x8A

movwf d1

movlw 0x03

movwf d2

loop2

decfsz d0, f

goto loop2

decfsz d1, f

goto loop2

decfsz d2, f

goto loop2

; Rest = 2 Cycles

goto Lazo

D20ms:

; Rutina de pausa de 20 ms

; Clock frequency = 4 Mhz

; Actual delay = .02 Seconds

; (20000 Cycles)

movlw 0xF8

movwf d0

movlw 0x1A

movwf d1

loop3

decfsz d0, f

goto loop3

decfsz d1, f

goto loop3

; Rest = 1 Cycles

nop

return

;**************************** FIN ********************************

end

This is the schematics: