I would like to trip the electronic Record/Playback mini kit (MK174) using a PIR detector (Quasar kit 3030) via a relay (Smart electronics kit 1168). All modules work correctly separately. I have managed to combine them all with the caveat of operating each board off a separate power supply - if I run the PIR and relay off the same supply (8*1.5V - AA batteries) the relay is automatically tripped once power is supplied to both boards. My question therefore is how can I isolate the power supply to each board and what is the best means of supplying kit mk174 with the required 4.5V from the 12V supply - should I use a regulator or can I use resistors?
Thanks in advance and apologies if this is not a good place to post.
Schematic diagram: http://tinypic.com/r/259xu84/5