start:
low c.0			;turn off interlock transistor
low c.2			;turn off pwm transistor
b3=0				;infrared detect pass counter
b4=0				;infrared detect fail counter
wait 1			;delay

loop1:
b2=0					;reset interrupt counter
for b0= 1 to 10			;start loop
setint %00000000,%00001000	;detect infrared status change
pwmout c.2, 25, 53		;transmit 38khz infrared, 50% duty cycle	
pause 5				;small delay
pwmout c.2, off			;turn off infrared
pause 5				;small delay
if pinc.1=0 then loop10		;check pb status
next					;continue loop

if b2=10 then loop2: 		;all 10 light transmissions received

sound c.4,(125,2)			;sound piezo (light detection fail)		
b4=b4+1 max 3			;increase fail counter
b3=0 					;reset detect pass counter
pause 400				;delay

goto loop3

loop2:
pause 400				;delay
b3=b3+1 max 3			;all light pulses recieved, increase counter
b4=0 					;reset fail counter	

loop3:
if b3=3 then high c.0 goto loop1 endif	;turn on interlock transister/led
if b4=3 then: low c.0 endif			;turn off interlock transister/led			
goto loop1						

interrupt:						;interrupt routine
pwmout c.2, off					;turn off pwm transistor
b2=b2+1						;increment interrupt counter						
return

loop10:
sound c.4,(124,5,123,5,124,5) ;acknowledge pb press
pwmout c.2, off					;turn off pwm transistor
high c.0						;turn on interlock transister/led
pause 60000						;pause 60 seconds
pause 60000						;pause 60 seconds	
goto start