Morning all, I've built the Velleman IR Light Barrier kit: http://www.vellemanusa.com/us/enu/product/view/?id=350693
It currently beeps when the light barrier is broken, but I'd like to remove the speaker and replace it with a reed relay to trigger another circuit. I imagine I'll also need to add some resistors in order to stop it from blowing the rest of the board, but am unsure how to work out what to add.
I've got a reasonable multi-meter, which can measure DC & AC current/voltage, resistance and capacitance. If I can measure what I need to using it, could you please describe how - I'm not sure whether I should be bridging the contacts on the speaker, or introducing the meter into the circuit in series...
Please let me know if any of the above makes no sense, I usually keep these projects inside my head, and don't know how many of the terms I've used are correct and how many I've made up.