Panic alarm

happysteve · May 11, 2014

tazz said:
Hopefully this will help, you can use any pa button, as this circuit takes virtually no load trough pa switch.
View attachment 24648

Forgot to add pa button in N/C open circuit to activate alarm.

Quick question about your circuit: are 12V relays ok with ~24V across the coil? (The node I would expect to be 0V, you have labelled -12V... perhaps I've misunderstood summat).

tazz · May 11, 2014

Used -12v for clarity to OP......using 0v tends to confuse.

pennychew · May 11, 2014

tazz said:
Hopefully this will help, you can use any pa button, as this circuit takes virtually no load trough pa switch.
View attachment 24648

Forgot to add pa button in N/C open circuit to activate alarm.

Thanks for that, im building some racking for the back of the van at the minute and i think i'll need to come back to that one later on tonight to get my head round it!

And you're right by the way, if you'd put 0v down i would have been totally stumped!

telectrix · May 11, 2014

just had a thought. to make it simple, use an emergency stop button. these are rated at several amps. OK, so they're meant for ac, but i'm sure a low dc current would not hurt.

pennychew · May 11, 2014

telectrix said:
just had a thought. to make it simple, use an emergency stop button. these are rated at several amps. OK, so they're meant for ac, but i'm sure a low dc current would not hurt.

I did have one of those in mind at first as it would be much simpler to just use one of those with a NO contact to break the supply to the sounder but i liked the idea of a latching panic switch that needed to be released with a key or tool, i can get hold of an E stop with a key i suppose as we have some in the stores at work but the chances are it will get hit by accident and they will lose the key!