Auto power on off for ESP Sound Board

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Dmurf
 
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Auto power on off for ESP Sound Board

Post by Dmurf »

I need to power on and off a Sound board automatically when a Model Train Engine becomes powered up for motion.
I have DC motor output I can tap into or motion itself could be sensed. A very small relay could work but the two circuits share common source but are separately controlled. When Motor is power close switch on Sound Board Ground or power would work if I can find a relay that closes with dc voltage in either direction. But i can't find such a device. Any help please. Dennis

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adafruit_support_mike
 
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Re: Auto power on off for ESP Sound Board

Post by adafruit_support_mike »

A reed relay with a diode bridge should work:
diode-bridge-relay.png
diode-bridge-relay.png (72.3 KiB) Viewed 102 times
The diodes guarantee positive voltage will always go to the top of the relay, and negative voltage will always go to the bottom of the relay.

If the voltage at MOTOR-A is higher than the voltage at MOTOR-B, current will flow through the diodes at the upper left and lower right.

If the voltage at MOTOR-A is lower than the voltage at MOTOR-B, current will flow through the diodes at the upper right and lower left.

You do lose some voltage through the diodes.. maybe 1.5V for silicon diodes, and 0.8V for Schottky diodes. That shouldn't be too much of a problem though. Reed relays only need 10mA to 15mA to close the switch, and aren't too picky about the exact voltage.

Diode bridges are common enough that they come as single-package parts:

https://www.digikey.com/en/products/fil ... EAEMAzilpA

and reed relays are affordable:

https://www.digikey.com/en/products/fil ... BIJYeOgmQA

Check the datasheets though: many reed relays have a built-in flyback suppression diode, which saves you one part in the final assembly.

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