Hello everyone, my first question here. Hope it's not too ignorant.

You know how audio stops playing when you unplug headphones?

I have a digital TENS machine that stops if the connection to an electrode is broken.

I want to use a Raspberry Pi to automatically switch a TENS channel between more than one electrode. I'll try using a relay or a transistor for that.

But how do I prevent the TENS unit from killing the current when I change to a different electrode? I want to seamlessly move the current from one electrode to another. The TENS unit only has two channels.

Does that question make sense?

Thanks a lot folks.

 

You can leave one connected until the next is connected (both are momentarily connected for a short time).
That should keep the TENS machine from disconnecting.

 

That makes a lot of sense. Thanks a lot.

While I'm asking questions, the TENS unit is rated at 180V, 70mA

Does anyone know the best way to switch that kind of signal?

I know zero about electronics, bar some basic theory.

Thanks a lot.

 

Does anyone know the best way to switch that kind of signal?

Probably a small relay.

 

What you want is called “make before break” . MBB

 

You can use p-channel mosfet and control exactly when you are making/breaking each one.

Something like this.

https://www.digikey.com/product-detail/en/on-semiconductor/SSN1N45BTA/SSN1N45BTACT-ND/3025282
To drive the gate of the P-channel like this one...

https://www.digikey.com/product-detail/en/microchip-technology/TP2640N3-G/TP2640N3-G-ND/4902388

 

Make-before-break in a single relay is rare. More common is to have two relays, and turn on relay #2 before turning off relay #1.

ak

 

More common is to have two relays, and turn on relay #2 before turning off relay #1.

That's what I was thinking would be the easiest.