direct current stimulation

[mihov1231]

I do not know much about eletronics, but I get around
Could you please help me with this

direct current stimulation
I need a battery powered constant current output of 1-2 mA,I have an Idea how to make this,
but I do not know how to cope with the skin resistance

It is important that the device is current controlled. What this means is that the device will adjust
the voltage up and down as the resistance changes so that the current never changes. For instance, if the
resistance of the skin is 10,000 ohms, then 10 volts will be needed to

 

[Hero999]

What's the maximum voltage?

A constant current source can be easilly be made with an op-amp or even a couple of transistors.

 

[mihov1231]

30 v

some guy told me to use something like this to solve skin resistance problem

http://www.national.com/ds/LM/LM334.pdf

 

[Hero999]

Yes, that should do the job.

 

[KMoffett1]

This is a constant current source I used as part of an iontophoresis current source for our Peds Pulmonary Function Clinic...many years ago.  The 67.5V battery was replaced with a 6vdc to 60VDC isolated DC-DC converter. The 60V gave us a wide dynamic range to compensate for skin resistance.

Ken

 

[Hero999]

I think you'll need to have more than 60V to ensure that 1.5mA flows,the resistance of dry skin can be very high and even with a saline solution you might not be able to go below 60k. The trouble is no more than 60V should be used for safety reasons as there's a chance the transistors will fail causing a dangerous current to flow. A good way to prevent this from happening is to place a suitable resistor in series to limit the current to a safe level, e.g. for 100V use 20k which will limit the current to 5mA or even better use two resistors in series so if one fails, there's another one still there to limit the current to 10mA.

 

[KMoffett1]

Was used for many years successfully and safely.  The idea of iontophoresis it to generate sweat on the skin and then analysis it. The circuit was also timed, and with over-current shutdown.

Ken

 

[mihov1231]

I was thinking of using this for tdcs transcranial direct current stimulation, my friend participated in an experiment and they used device with this characteristics http://www.newronika.com/products_hdcstim.html

I do not know how they power the device with
# Power: 2 batteries type AA/LR6

 

[Hero999]

Was used for many years successfully and safely.

You're right of course but this means nothing if when the 'what if?' brigade get involved in order for a device like that to get medical approval. The general rule is that no single point failure shall endanger the person using it. Now as far as both you and I know, transistors are reliable and it's unlikely that the transistor will fail causing the person to be connected directly to 67.5V but it is possible so in order to be approved another form of protection would be required. Fortunately 67.5V is still low enough that it's unlikely that a deadly current will flow but it will give a nasty shock.

I was thinking of using this for tdcs transcranial direct current stimulation, my friend participated in an experiment and they used device with this characteristics http://www.newronika.com/products_hdcstim.html

I do not know how they power the device with
# Power: 2 batteries type AA/LR6