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Hi everyone,

I have searched the forums and the internet but could not find an answer.

I want to make a TENs machine that I can control (http://en.wikipedia.org/wiki/Transcutaneous_electrical_nerve_stimulation)

I have an old tens machine that I have taken apart but I have not been able to find any circuits or manuals for it on the internet. It is a Boots model 2BT on the case but this seems to be a white labelled device. The circuit board names it as "Ultima tens (m) 7". Here is a link to another rebranded one but it looks exactly the same: https://www.tenscare.co.uk/index.php?action=products&product=108

I have found this circuit for a TENs machine:
http://tinypic.com/view.php?pic=wlsm0n&s=1

My question is - would I be able to repurpose the existing machine that I have so that I can control it?
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You need to be exact about what you mean by controlling it.
You could certainly use an arduino to replace the manual controls.
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Thanks for the reply.

The device has two outputs that each attach to a pad used to transmit the pulse of current.

The device  allows you to control the pulse frequency, pulse width and intensity of the current that it passed onto the output pads.

Rather than create a pulse, I would like to be able to program the arduino to create my own "patterns" of pulse as it were.

For example, 500ms of a certain intensity, then 1500ms of a different intensity, then a 2 second pause, then back to the start.

I am comfortable with the programming side of things and have run through the tutorials.

I can upload pictures of the device circuit board if that helps?
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Anyone have any ideas?
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Not really sure what you want to do. When you say repurpose, do you mean just tap into the existing controls? Do you mean hack it and take over completely? Either are possible. Notice that every schematic you find will have two timers and a set of FETS at the output. The 80V signal is applied to the FETS and controlling the gate of the FETS turns that signal on and off to create the pulse width, duration, etc... So you could determine which part of your existing device is that final output switch (the FETs) and just take over from there.

Essentially you have a mixer/modulator. Your 80V signal would be your "carrier". You pulse that with the desired frequency. Adjusting the pulse width of that frequency will control the intensity or amplitude since your body is basically a low-pass filter. Those signals are always present at the point of the FET. You then just turn the FETs on and off to control the pulsing effect. If you have multiple outputs, you can also control the pattern this way. And of course you can turn it completely off by timer this way.

I don't typically do nagging about safety, etc... since I am not anyone's mother, but please understand the safety aspects of using these before messing around too much with it. The current in these is very low, but you still should never put the electrodes in a path that will cross the heart (basically arm to arm.) If you build your own, you need a very stable constant current supply, isolation, and current limiting in the output. To be extra safe, it would be good to have current feedback and if the current ever goes up, you would shut things down. Repurposing your original device may be a good idea because it will (hopefully) have all these safeguards built in. Though, they are supposedly illegal to manufacture in the united states for home use, so no guarantee that they actually passed any kind of official testing for safety.
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Thank you, that is a great help.

I understand about the safety element (I am a medical doctor) and I will be careful. It is battery powered as well.

The device I have is imported by the largest drug store in my country and they are careful when it comes to medical devices.

Thank you again.

Tom
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