I have one unit of museum cabinet detector that works on 18v. I want make simple security circuit with detector. I've figured out that two output ports on detector are normally contact(NC), but it'll shows ~150mV difference charge when it sensed something. So main alarm system get signal. I have only units and I need to control it with my circuit with battery.
I assume It is quite simple logic so I sorted out with arduino at the moment. (Analog input from the detector, digital output to latch up alarm circuit. Alarm rings whenever it get signals for 3 seconds.)
But I believe there must be much simpler way to build it by only electronic components. I tried to sense voltage changing of the detector with FET, Opto-coupler, relay but has failed. Probably my component's specification doesn't match well with the situation but also I am not sure if I approach proper way.
When activated voltage changes 0~150mv what would be best and cost efficient way to detect the signal so that alarm circuit could get it as input?