Monitor old home security system zones with Pi - Raspberry Pi Forums

i have old home security system monitor status of zones. it's 8 zone system. voltage @ zone terminal connection reads 6v dc secure zone , 13vdc unsecured zone. have tried use lm324 comparator give low 0v secure zone , high 5v unsecured zone comparators output limited 0 or supply voltage of comparator , input voltage cannot exceed supply voltage.

here schematic system(last page) - http://scansecurity.net/manuals/napco/n ... %20850.pdf

not trying control inputs. need simple status reading 2 voltages. ideas of how 6 , 13 volt reading high or low reading raspberry pi can handle?

i'm new electronics , pi , appreciate advice or direction head more research.

- jerry

hi.

may able simple voltage divider, :-


may because adding resistances alarm zone wiring can have unexpected results.
suggest try using meter before connect pi , test alarm make sure still works circuit connected zone terminals.
chose high values in hope not affect existing circuit, using these values should find 13v input give 2.1v on gpio terminal , 6v input give 0.98v should give gpio high , low accordingly.
edit. of course need 1 of these circuits each zone wish monitor

hope helps , once again
please test before connecting pi

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