This project has been created as an add-on for the 2-Digit Counter. We placed the two transistors, LDR's and pots on a small PC board and connected it to the 2-Digit Counter via a plug and socket.

The light detectors have to be set up for the application. The best is to use infra-red detectors as they are not upset by ambient light.
Each detector has to be set up so that light falling on the detector makes the input line LOW.
When the beam is broken, the line goes HIGH.
We have directly coupled the output of the detector to the micro however you could use capacitor coupling  and breaking the beam will produce a pulse.

The files for Lift Counter
LiftCounter.asm  
LiftCounter.hex
LiftCounter-asm.txt (.asm)
LiftCounter-hex.txt (.hex)
 

;************************************************ ; Lift Counter Started 8/8/2009 ;Count the number entering and leaving a lift ;Port B drives 7 segment display ;enter on RA2 exit on RA3 ;Units drive on RA0 Tens drive on RA1 * ;* * ;************************************************ list P = 16F628 ;microcontroller include ;registers for F628 __Config _cp_off & _lvp_off & _pwrte_on & _wdt_off & _intRC_osc_noclkout & _mclre_off ;code protection - off ;low-voltage programming - off ;power-up timer - on ;watchdog timer - off ;use internal RC for 4MHz - all pins for in-out ;********************************************* ; variables - names and files ;********************************************* ;Files for F628 start at 20h temp1 equ 20h ;for delay temp2 equ 21h ;for delay SwUp equ 22h ; SwDwn equ 23h ; units equ 24h ; tens equ 25h ; Sw_Flag equ 26h ; counter equ 27h ;max count is 2Hz ;******************************************** ;Equates ;******************************************* status equ 0x03 cmcon equ 0x1F rp1 equ 0x06 rp0 equ 0x05 portA equ 0x05 portB equ 0x06 ;******************************************* ;Beginning of program ;******************************************* reset org 00 ;reset vector address goto SetUp ;goto SetUp table addwf PCL,F ;02h,1 add W to program counter retlw b'00111111' ; "0" -|F|E|D|C|B|A retlw b'00000110' ; "1" -|-|-|-|C|B|- retlw b'01011011' ; "2" G|-|E|D|-|B|A retlw b'01001111' ; "3" G|-|-|D|C|B|A retlw b'01100110' ; "4" G|F|-|-|C|B|- retlw b'01101101' ; "5" G|F|-|D|C|-|A retlw b'01111101' ; "6" G|F|E|D|C|-|A retlw b'00000111' ; "7" -|-|-|-|C|B|A retlw b'01111111' ; "8" G|F|E|D|C|B|A retlw b'01101111' ; "9" G|F|-|D|C|B|A ;**************************************************************** ;* port A and B initialisation * ;**************************************************************** SetUp bsf status,rp0 movlw b'00001100' ;Make RA0,1 out RA2,3 in movwf 05h clrf 06h ;Make all RB output bcf status,rp0 ;select programming area - bank0 movlw b'10000000' ;Turn off T0CKI, prescale for TMR0 = 1: movwf option_reg clrf portB ;Clear Port B of junk  clrf units ;zero the units file clrf tens ;zero the tens file clrf Sw_Flag movlw 07h ;turn comparators off and enable movwf cmcon ; pins for I/O functions goto Main ;************************************************ ;* Delay 10mS 10 x 1,000uS ;****************************************** D_10mS movlw 0Ah movwf temp2 D_a nop decfsz temp1,1 goto D_a decfsz temp2,1 goto D_a retlw 00 Up btfsc Sw_Flag,2 retlw 00 bsf Sw_Flag,2 incf units,1 movlw 0Ah ;put 10 into w xorwf units,0 ;compare units file with 10 btfss status,2 ;zero flag in status file. Will be set if units is 10 retlw 00 clrf units incf tens,1 movlw 0Ah ;put 10 into w xorwf tens,0 ;compare units file with 10 btfsc status,2 ;zero flag in status file. Will be set if tens is 10 clrf tens retlw 00 ;display passes 99 but not below 0 Dwn btfsc Sw_Flag,3 retlw 00 bsf Sw_Flag,3 decf units,1 movlw 0FFh ;put FFh into w xorwf units,0 ;compare units file with FFh btfss status,2 ;zero flag in status file. Will be set if units is 10 retlw 00 movlw 09 movwf units ;put 9 into units file decf tens,1 movlw 0FFh ;put 0FFh into w xorwf tens,0 ;compare tens file with 0FFh btfsc status,2 ;zero flag in status file. Will be set if tens is 0FFh goto $+2 ;tens file is 0FFh retlw 00 clrf tens clrf units retlw 00 ;display not below 0 ;**************************************************************** ;* Main * ;**************************************************************** Main movlw 040h ;maximum count is 2Hz movwf counter ; Main1 btfss portA,2 ;test for enter (will go HIGH on enter) goto $+3 ;entry not detected call Up goto Main2 btfss portA,3 ;test for exit (will go HIGH on exit) goto $+3 ;exit not detected call Dwn goto Main2 clrf counter incf counter ;effectively bypass counter ;DISPLAY DIGITS Main2 movlw b'00000001' ;Make RA0 HIGH for units drive movwf portA movf units,0 ;copy unit value into w call table ;unit display value will return in w movwf portB ;output units value call D_10mS ;call delay clrf portB ;clear display movlw b'00000010' ;Make RA1 HIGH for tens drive movwf portA movf tens,0 ;copy tens value into w call table ;tens display value will return in w movwf portB ;output tens value call D_10mS ;call delay clrf portB ;clear display btfsc portA,2 ;bit 2 is zero when enter LDR illuminated bcf Sw_Flag,2 btfsc portA,3 ;bit 3 is zero when exit LDR illuminated bcf Sw_Flag,3 decfsz counter goto Main2 goto Main END