On Wed, 21 Jun 2006 08:35:20 -0600, Mike McWilliams <mmcwill@xxxxxxx>
>Alan B wrote:
>> On Fri, 16 Jun 2006 13:14:43 -0600, in message
>> <1150485283.80861@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Mike McWilliams
>> <mmcwill@xxxxxxx> scribed:
>>> I'm interested in researching scorpion venom, and have come across
>>>descriptions using DC voltage to stimulate venom excretion. Ranging from
>>>6v DC at 120ish hz to 1.2kV at 10hz.
>>>What I would like to do is use my computers sound card as a function
>>>generator to allow me to change the frequency for the voltage desired.
>>>I would imagine that sound card output is well below the voltages I
>>>require, and from what I understand is AC coupled.
>>>I would therefore like to take the signal generated, and use it to
>>>modulate a separate DC source at the frequency of the generated function.
>>>My question is what would be a good place to start in terms of
>>>components? I have little experience in electronics design, though I
>>>have put a few kits together.
>> Ah well, I found this site:
> So 1250 kV at 0.5 hz
>not too far out of the range I gave now is it. Plus it follows the trend
>I've indicated that at high voltage, frequency is low.
>> and notwithstanding its very general description about the electrical
>> design, it doesn't mention anything about DC offset. Given your garbling
>> of terminology, i.e. "6v DC at 120ish hz," my guess is you've not done
>> enough research about what you need just yet. A web search on "Arthropods
>> Electronic Stimulator" didn't yield anything outside the given article. I
>> recommend a visit to the local college library. Once you're a little more
>> clear about your design needs, you'll get better help here.
>How about you leave the biology to me, and the electronics to my next
>visit to the local college library. electrically stimulating scorpions
>to harvest venom is something that is just not covered in books. You
>can't order a power supply specifically made for this purpose.
I've done a lot of electronics for biological purposes.
I wonder if maybe the waveforms used in the article are
actually pulses or pulse trains. All the biological stimulators
I have ever seen were pulses. The typical approach is to
use a bipolar (biphasic) pulse, where the no-signal condition is at
0 V and each pulse goes positive for a duration and then negative
for a duration, followed by a return to zero for a dwell period..
These biphasic pulses are then repeated at some pulse repeat rate.
They are often used as trains of some number of pulses followed
by a silent interval.
The biphasic approach is used to avoid delivering net charge to
the subject, and also to avoid (or reduce) any plating reactions
at the electrodes. Stimulators may allow independent control
over the duration and amplitude of the positive and negative
phases for those situations where you want to have no net
charge, but give a big positive pulse with a narrow duration
followed by a smaller negative pulse with a longer duration that
balances the charge.
I mention all this because a pulse-type stimulator might be
much easier to build than amplifying a low-level signal,
if you really want the high voltages. Since the output
devices are either off or on, they are simple switches and
don't need to dissipate much power themselves.
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