
The microphone bioamplifier - sasvari
http://www.windytan.com/2015/10/the-microphone-bioamplifier.html
======
raverbashing
Working with biosignals is a very interesting field of work

As noted, the mains hum is a major source of havoc. It is usually filtered
very strongly (and you usually have to do some analog filtering, otherwise
you'll get less of the original signal that you want - this also adds issues
like phase distortion, etc)

You also have to use very low-noise/high-impedance input amplifiers, so either
get the expensive parts or do something like this:
[http://www.allaboutcircuits.com/textbook/semiconductors/chpt...](http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/building-
a-differential-amplifier/)

~~~
whoopdedo
> As noted, the mains hum is a major source of havoc.

Use batteries? Or whatever is the most stable way to generate direct current.
Turning a dynamo maybe or is that too simplistic?

~~~
raverbashing
Batteries won't help. Because a person (to which the circuit is attached) is a
very good antenna picking up the hum from the wires around.

Filtering the 50Hz/60Hz from the power supply is relatively easy.

~~~
moron4hire
Needs a humbucker pickup!

[https://en.m.wikipedia.org/wiki/Humbucker](https://en.m.wikipedia.org/wiki/Humbucker)

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deutronium
I thought
[https://www.youtube.com/watch?v=iVXOjVZNfhc](https://www.youtube.com/watch?v=iVXOjVZNfhc)
was fascinating regarding EMG signals too.

Theres also some really amazing research attempting to decode inner speech via
EMG - [http://ti.arc.nasa.gov/m/pub-
archive/471h/0471%20(Jorgensen)...](http://ti.arc.nasa.gov/m/pub-
archive/471h/0471%20\(Jorgensen\).pdf)

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pragone
An EKG electrode needs to be Ag/AgCl to be reliable. Making your own is a good
start to poor results.

~~~
moron4hire
I find this comment extremely unhelpful. Where would she be likely to find
silver or silver chloride in her house right now in a convenient way to be
able to make the electrode? The only silver I have in my house is a spoon my
grandmother gave me (I don't get old people's fascination with spoons), so
personally I wouldn't be inclined to monkey around with it, if I could get
good enough results out of something else. And I assume she wants to use
something lying around in the house because if she were to have to order
something she might as well just order real electrodes.

Your comment comes off as "this other way that you are not doing is the best
way, so you way may as well not even try". This is _Hack_ er News, after all.
A hack is, by definition, slapped together from what's available on hand.

~~~
ggoss
Silver can be chlorided quite easily by immersing it in bleach for a short
while (10 sec to a few min). The color should change, from the bright silver
you know and love to a dull, darker gray. You can buy Ag wire for this
purpose, or, I imagine, creatively salvage some from another source.

~~~
mannykannot
EKG electrodes seem to be readily available, and cheap, too, in the US. IIRC,
even the hypo-allergenic ones I had to get one time were not particularly
expensive. I don't know if the rules are different in Finland.

[http://www.amazon.com/Kendall-Covidien-200Series-
Electrode-F...](http://www.amazon.com/Kendall-Covidien-200Series-Electrode-
Foam/dp/B0054K7ENC/ref=sr_1_3?ie=UTF8&qid=1443893504&sr=8-3&keywords=ekg+electrodes)

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sigmar
This isn't a "microphone" at all. Microphones by definition transduce the
physical movement of sounds waves into a signal. This is just using the sound
card to sample the electrical signals picked up by the conductive leads.

~~~
pygy_
It is not a microphone, but a mic (bio-) _amplifier_ , which is indeed good
enough (bandwidth- and power-wise) to sample muscle signals.

~~~
sigmar
It is definitely good enough to sample the signals. But why use an inaccurate
title? Wiring something into a soundcard doesn't make it a microphone.

~~~
pygy_
"microphone" qualifies "amplifier", meaning that it's an amplifier designed
for processing signal coming from a microphone.

The title is a word play summarizing the fact that the author used such an amp
to record biological signals. In context, it doesn't means or even imply that
he uses a microphone.

Edit: word play, not pun; Edit2: +s; 3: better still.

~~~
moron4hire
*she

~~~
pygy_
*I wish English had a proper personal, gender-neutral pronoun.

Editing, anyway.

~~~
pluma
They. Yes, if you're not familiar with it, it looks like the plural form, but
it has been used to denote individuals even before "political correctness"
became a thing.

~~~
mdpm
Thon could also use
[https://en.wiktionary.org/wiki/thon](https://en.wiktionary.org/wiki/thon)

edit: that part meant jokingly (please). Although
[https://en.wikipedia.org/wiki/Old_English_grammar#Pronouns](https://en.wikipedia.org/wiki/Old_English_grammar#Pronouns)
is far more interesting.

