Tech Forum

I’m looking for a circuit using a piezo buzzer, that I can hear from the room above the cellar. It will be connected to a Taco Heating Zone Valve on the boiler in the cellar for troubleshooting the thermostat when it goes on and off.

Get a DC-DC converter like this one:

DC-DC Buck Step-down Regulator Converter 4.5~65v to 3V 6V 9V 12V 24V 48V Module

Get a diode, resistor and capacitor per the schematic and build the new circuit. Note the capacitor must be rated at least 35 volts. Connect the new circuit to the existing circuit, A to A and B to B.

The diagram shows a doorbell push button - more on that later. In place of the doorbell push button you can connect whatever piezo you want that is within the capability of the DC-DC converter you get. The problem with piezo buzzers is that it is impossible to predict whether you will hear them from the room above.  A cheap (<$10.00) solution is to use a wireless doorbell. For that, read on.

Get a wireless doorbell from eBay like this one: https://www.ebay.com/itm/400ft-Wireless-Doorbell-Twin-Wall-Plug-in-Waterproof-Cordless-Door-Chime-Kit/152986512099?hash=item239eb4eae3%3Am%3Amxl6HSV0iPKKQ83VnZkaAfw&LH_BIN=1

Set the output voltage of the DC-DC converter to match the battery voltage of doorbell push button circuit. The battery will not be used. Short the switch contacts inside the doorbell push button.

When the thermostat sends 24 VAC to the Taco, the DC-DC converter will output whatever voltage it is set to to make the wireless doorbell chime or the piezo buzz. When the thermostat is open, there will be no voltage out of the converter.