Hi to all. I have a simple(I think) problem that I'm hoping someone can help me with. I want to connect a remote transmitter / receiver pair ( garage door opener type thing) to an alarm system magnetic switch.When the door/ window is opened it sends a signal to the receiver and activates the relay. Hope I'm getting the idea across. I only have normally open switches. If the door/window is closed and the magnet is near the reed switch it is CLOSED. Does anyone have any idea how I can connect the xmitter to this arrangement so that it is turned on when the switch becomes open. It must draw no power while closed.(battery operation) The obvious answer is use a switch that is open when near the magnet and closed when moved away(N/O) , and connect this to the button of the xmitter , But I don't have this type of sensor. My initial idea was to connect the xmitter from Batt+ to gnd through a PNP transistor(emitter) , collector to GND. The base connected to Batt+ via mag switch and the base to GND via a resistor.The switch keeps the pnp off until it opens and the resistor turns the transistor on.Problem it the constant current draw via the switch and resistor.
Any clever ideas how to get this arrangement to work? Hope I'm not being to vague in my description.
Cheers Rob