Hello everyone. I'm working on a project and designing an Electrical Stimulation Device. It is a pulsed bi-phasic electrical stimulator. I want to know what are the safe current limits for pulsed bi-phasic electrical stimulation? I need to implement a current sensor and program it to stop stimulation if amplitude of current increases than the safe limit.

 

As a matter of opinion, I think it's less than 0.01 amp. I also think you are lacking information. This kind of machine is so old that I have repaired them when they looked like a music box inside, made of a motor turning gears under spring loaded switches. I have also worked on the 9 volt, pocket size version. You think you can "program" your way out of this problem. I think the current limits are easily established with a resistor or two which do not depend on an over complicated, un-repairable microprocessor.

 

Thank you for your reply. By 'program' i meant I'll employ a current sensor and code the microcontroller to shut the stimulation off in case of over-current flow.
I am using a 9V battery as the source. The stimulator output voltage is 50V peak-to-peak. This is achieved using a Boost Converter circuit. The only thing I can't figure out is the maximum current that should be allowed for safety.

 

Most any current in excess of 5 milli amps will be painful and produce a "let go" reflex.

Currents of 1 to 3 milli-amps are threshold and are just perceptible as a tingle or shock.

DC and power line frequency voltages are most noticed by humans and increasing frequency reduces human perception of the shocking sensation.

 

I would say, "Plug yourself in and see how much current is required to hurt you" but every person is different. That's why electrical stimulation machines have adjustment knobs on them. When you decide what you will set for a current limit, that is easily done with a resistor or two installed in the power circuit. No programming required.

 

My TENs unit is rated for up to 105 ma into a 1k load. I can take it up to about 85 on some narrow pulse modes but only 25 on other wider ones.

Depending on where you put it on your body also makes a big difference. On the back of my neck 10 - 15 ma is plenty high but on my lower back I don't really start feeling it until 30 ma and up.

 

My TENs unit is rated for up to 105 ma into a 1k load. I can take it up to about 85 on some narrow pulse modes but only 25 on other wider ones.

Depending on where you put it on your body also makes a big difference. On the back of my neck 10 - 15 ma is plenty high but on my lower back I don't really start feeling it until 30 ma and up.

Could you tell me what TENS unit do you use? and does that unit display this intensity on its screen?
In my case, my application is stimulation of the gluetal muscles (buttocks).

 

on my lower back I don't really start feeling it until 30 ma and up.

What I find is that the current density at the connections to me become painful when I can't feel anything in the muscles, but it is still effective when I turn the power down enough to avoid the pain at the attachment points. Still, I don't have a clue as to the peak current in the fast pulses which are applied to me.

 

It is not the current that has the effect. It is the voltage. And the voltage must change polarity for the muscle to react.
You almost cannot feel 120v DC but 120v AC at 10 microamps will throw you across the room.
I have a zap circuit on 3v - producing 120v DC on a trick greeting card. The circuit takes a few mA and throws you across the room.
You can begin to feel 35v AC at a low frequency.
You only need the voltage to activate the muscle.

 

Please be very careful with this project. Get a book on medical electronics design and study it. You can stop your heart if your not careful. Yes, really.

 

why build one? I got one for my daughter for christmas, it was about $40.00 for a new one.

 

I bought one for $8.00

 

It is not the current that has the effect. It is the voltage. And the voltage must change polarity for the muscle to react.
You almost cannot feel 120v DC but 120v AC at 10 microamps will throw you across the room.
I have a zap circuit on 3v - producing 120v DC on a trick greeting card. The circuit takes a few mA and throws you across the room.
You can begin to feel 35v AC at a low frequency.
You only need the voltage to activate the muscle.

I call BS all the way around.