TENS modification

how do i modify this circuit so i can control it with a PWM signal from the arduino instead of the 555 Timer IC ?

555-Timer-IC.jpg

High-Frequency-Tens-Machine-Wave-Asymmetrical-.jpg

Take the first circuit on this page:- http://www.thebox.myzen.co.uk/Workshop/Motors_1.html Remove the diode and the motor and substitute your two pads and resistor / LED.

thanks, your idea really helped, but for muscle stimulation i need a way to change frequency in the 0-150 Hz range, the arduino pwm pins output a default 490 Hz and it is too much. Any functions to change that? or maybe some hardware tweaks to the circuit?

P.S.
i also need a way to change voltage and current, i could probably do that with resistors or potentiometers, but in muscle stimulation frequency is more important

P.P. S
here is the diagram of the circuit as it is now. as you can see i have 4 sets of electrodes (meant for 4 muscles) and they will be programmed to work in pairs (will probably use only 2 pwm pins instead of 4). Also i’m using mosfets instead of transistors

i need a way to change frequency in the 0-150 Hz range, the arduino pwm

Just google:- arduino pwm frequency change

i also need a way to change voltage and current

No the voltage output from the arduino is a fixed logic level. The current output depends on the load.

here is the diagram of the circuit as it is now.

Thanks

as you can see i have .......

Sorry I can't make head nor tale of that schematic. Too many loose ends, what is connected to what?

Just google:- arduino pwm frequency change

did it before asking, all i can find is how to change the frequencies to specific values like 30, 61, 122 Hz. I need the frequencies in between, in order to fine tune the stimulator so as to get the adequate muscle response. In other words i need to change the values in real time.

sorry about the schematic, is this version better?

Well this tells you.
http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM
Note the frequency is not continuously variable, its resolution is the least significant bit in the counter. Maybe you are not understanding the examples.

That circuit :-

  1. Needs a common ground with the arduino.
  2. Is 9V enough to work for a TENS?

Ok i'll read into this and try to understand it lol

That circuit :- 1) Needs a common ground with the arduino. 2) Is 9V enough to work for a TENS?

The working circuit is right next to me on a breadboard, and i have a common ground, just forgot to show it in the schematic. 9V is more than enough for a Frog muscle tens (yes, i'm torturing frogs in our lab at med school) even 400mV-1V will work (that's why i asked how to reduce the voltage). Theoretically it is enough for human muscle too, nerve fibers operate at 60mV-90mV and for muscles it's generally a bit higher but varies depending on the muscle.

I see i did not know it was a direct connection, I thought it was going through pads.

That circuit only gives a voltage / no voltage, is that what you want? I would have thought you needed a voltage and then the reverse a bit like a motor running in either direction. You need a h-bridge circuit for this. The simplest way to drop the voltage is to use a potential divider on the output.