Posted by PJH on February 10, 2010 at 21:20:09 from (72.69.100.123):
In Reply to: Re: Barn phone ? posted by Ecnerwal on February 10, 2010 at 20:26:28:
That's the exact circuit that we used, Lawrence. I thought we'd have to do a bunch of part swapping to get it to work, but it worked the first try. Seems like we might have used a different supply voltage, but calculated the resister value for 25 ma. We used heavy resisters as the designer recommended. I thought that both piezos buzzed when one phone was lifted off hook, but after reading the text with the schematic, I think only the on hook piezo buzzes, and the off hook phone picks up the buzz in the receiver.
I'd use caution building something like this. It would be wise to monitor the results for a while after powering it up, watching for overheating components.
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