The microphone bioamplifier | Hacker News Reader

The microphone bioamplifier

windytan.com

49 pointssasvari25 comments

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...

> 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?

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.

Needs a humbucker pickup!

https://en.m.wikipedia.org/wiki/Humbucker

Batteries or very clean PSUs help, but you can pick up mains hum even if your measuring device is not connected to the power grid. Every cable and even the body your measuring on pick it up. Simple demonstration: hold an oscilloscope's probes in your hand and you'll clearly see 50/60 Hz showing up.

Interestingly, this is used to geolocate multimedia recordings, as different places will have different mains interference.

If you know roughly when a recording is taken and what the state of the power grid over the target area (country, region or state etc.) is, you can match the recording with its location - and vice versa.

https://www.ece.umd.edu/~minwu/public_paper/Conf13/1305_ENFL...

I thought 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)...

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

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 Hacker News, after all. A hack is, by definition, slapped together from what's available on hand.

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.

Yep, this is the "easy" way to chloride silver wires in the lab. I've chlorided silver wires by immersing part of the wire in bleach (regular household Clorox) and taping it in place so it sits for ~10-20 minutes.

Silver wire is pretty cheap online, so it's not too hard to get started.

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...

In what way are the results degraded by a different choice of ions?

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.

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

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.

"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.

*she

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

Editing, anyway.

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.

Thon could also use https://en.wiktionary.org/wiki/thon

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

The proper personal, gender-neutral pronoun in English is "they"

Yeah but "that they" is awkward.

I took it as a wordplay on "microphone amplifier" and "bioamplifier"

By definition https://shkspr.mobi/blog/wp-content/uploads/2013/08/Zoolande... is a microphone

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