Prevent current stopping when connection is broken.

Discussion in 'General Electronics Chat' started by Monkeybus, Jan 16, 2018.

  1. Monkeybus

    Thread Starter New Member

    Dec 29, 2017
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    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.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    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.
     
  3. Monkeybus

    Thread Starter New Member

    Dec 29, 2017
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    0
    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.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Probably a small relay.
     
  5. ElectricSpidey

    Active Member

    Dec 2, 2017
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    What you want is called “make before break” . MBB
     
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  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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  7. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    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
     
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  8. crutschow

    Expert

    Mar 14, 2008
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    That's what I was thinking would be the easiest.
     
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