DAC Controlled Current Source for Human use

[efelnavarro09]

Hello everbody, I'm working on a T. E. N. S. machine that generates different waveforms, all coming from a CPLD. Well my question is How do I make a variable current source from 0 up to 150mA controlled by voltage (3.3V) that will be connected to the electrodes. Also I will appreciate if anyone can explain to me what does "through 500ohm resistance" means in commercial TENS machines? Thanks in advance.

 

[KMoffett]

"through 500ohm resistance" means the current was measured through a 500Ω load that simulated the conduction path through the the electrodes and a human body.

Google: voltage controlled current source

Ken

 

[efelnavarro09]

KMoffett, thanks for your reply. So If I understand what do you explain, I need to calculate the resistors values in the V2I converter considering a 500Ω Load? Thanks

 

[KMoffett]

Yes...if that's the likely body impedance. My guess is that it will be higher. Remember that the current source will have to have enough compliance (supply voltage overhead) to deliver the selected current at the worst case, but acceptable body impedance.

Ken