home alarm

I want to use ceiling mount motion sensors for a home alarm.
they have NC contacts when no motion.
I need to interface with a 110VAC lighting contactor.

what I will have is 12VDC for all the external sensors and the horn and also a key switch. then the 110VAC

the whole unit is very simple the key signals either occupied or unoccupied. when in the unoccupied mode, any change of the input on the sensor will signal an alarm. the alarm will stay until the key is used to deactivate.

the 1110VAC will be on the contacts of a latching relay on the PCB.

couple of questions. for the 110, do I need to use 3 wire, with a ground and put something like a guard ring around the 110 ?
they will be on one side only, on a corner of the board so there are no DC traces on the opposite side or in close proximity. the use of a milled separation is possible.

as for the logic, I was thinking either a LM393 or a ATTINY85. it seems that the LM393 would need more external chips, a voltage divider for the threshold and such. maybe a pot for adjustment.

The only other output would be an LED to indicate the switch position. that could be from the ATTINY or hardwired.

I am leaning heavily on the ATTINY as I could use momentary switches and make it easier for layout.

As I see the board, I need 2 inputs, one from each sensor.
1 input from the key
1 output for the relay and maybe 1 output for the LED.

Since timing is not an issue, I would use the internal oscillator at 1kh.

The program seems simple as well, a debounce and then just look for the signal.

I would use an UNO for programming so I do not need a USB port.

I think the only fence sitting is that with the ATTINY I have to use a voltage regulator, with the LM393 I can use 12V for everything.

// rambling mode off

suggestions or comments ?