On Tue, 8 Jul 2008 07:36:11 -0400, "Tom Biasi"
wrote:


"sal2" wrote in message
news
Greets All

I'm trying to amplify my audio from my computer sound card and turn it
into a Tens machine. So I need to increase the current/voltage do you
guys know/recommend the best way to go about doing this? The
frequency range I plan to use is from 1Hz to 20KHz.

Aloha
Rick

Not a good idea to hook yourself up to a device that is supplied by line
current.
Medical devices are strictly designed.

Agreed, but see below.

If its a battery powered laptop it would be safer but the sound card will
probably not do what you want.


It's been a long time since I looked at TENS, but my recollection is
that they used rectangular pulses. If so, then you could use an
optoisolator on the output of the sound card, driving a battery
operated stimulator. Note that sound cards are AC coupled,
so the "zero" baseline will move when you change the duty cycle.
You may want to use a zero-recovery circuit ahead of the optoisolator,
if you are going to be changing the duty cycle far from 50%,
especially if you are hoping to use the sound card level controls to
control the stimulator level. Optoisolators are a lot simpler if they
only have to pass on/off signals, so it would be better to drive the
optoisolator from a comparator to insure a solid output, and just put
a level control knob on the stimulator.

If you really want to control the level with the sound card, you might
want to use the second stereo channel to do that, again feeding it
through a comparator and optoislator. Generate a pulse train on
that channel whose duty cycle is proportional to the desired level,
and then just filter the optoisolator output to get a DC control
signal for the stimulator.

The sound card should have no trouble producing signals in the 1 kHz
to 20 kHz range (using a 48000 Hz sample rate), but the output may be
reduced at the high end. That shouldn't be a problem if you are
feeding it to a comparator anyway.

SHAMELESS PLUG: You might want to look into the signal generator
features of my Daqarta software. You don't need to buy anything:
The generator is absolutely FREE, forever, even though certain other
features like input monitoring will stop working after the trial
period. You are welcome to use it that way as long as you like.
It has extensive pulse generation options, including the ability to
use Pulse Width Modulation, FM, AM, sweeps, bursts, etc.

Best regards,


Bob Masta

DAQARTA v4.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!