I've been trying to use some piezo sounders salvaged from a couple of burglar alarm exterior sounders to make a horn that uses less power than a car horn for starting sailing races. I have salvaged one sounder with associated auto transformer and darlington transistor from one alarm and two sounders with one auto transformer and a mosfet from the other.
I have built a rectangular wave 555 circuit with variable frequency in the audio range and duty cycle variable from about 30 to 70 per cent. I'm running the 555 on 12V. I've got this set up on a breadboard using the single piezo sounder and its associated auto transformer and I can set the frequency and duty cycle to an optimum. However I am still disappointed with the volume. I would expect it to be uncomfortably loud when it's sitting on the bench in front of me and it's not.
I've been wondering whether the answer is just to increase the voltage - I know burglar alarms normally work on 12V - could they be converting to 12V AC which would be equivalent to a 24V square wave from the 555? Should I use all three piezo sounders in parallel? In which case would I need the second auto transformer?
I'd be grateful for any thoughts or advice.
Russell
I have built a rectangular wave 555 circuit with variable frequency in the audio range and duty cycle variable from about 30 to 70 per cent. I'm running the 555 on 12V. I've got this set up on a breadboard using the single piezo sounder and its associated auto transformer and I can set the frequency and duty cycle to an optimum. However I am still disappointed with the volume. I would expect it to be uncomfortably loud when it's sitting on the bench in front of me and it's not.
I've been wondering whether the answer is just to increase the voltage - I know burglar alarms normally work on 12V - could they be converting to 12V AC which would be equivalent to a 24V square wave from the 555? Should I use all three piezo sounders in parallel? In which case would I need the second auto transformer?
I'd be grateful for any thoughts or advice.
Russell