Saturday, June 8, 2013

Fun with Electronics

Dear reader, I occasionally run off on a fad.  (I insert here that the wife would take issue with "occasionally".)

Not a clothing/fashion fad, mind you, as I have little sense for such things, despite much effort & patience on the part of my sainted wife.  No, the fads I am referring to involve intellectual ADHD.  And typically come at a time when things are not going well with woodworking.

Fortunately, it doesn't take much to take off on a tangent.  I have the starting materials to veer off into gardening (successfully), woodworking, electronics (see below), lockpicking, robot building (Myra's favorite; no I did not build that), jewelry making, tile work, and outdoor construction.  So when I need to take a break from woodworking, it means very little capital outlay.  Which is good, as we have very little capital inlay.

For Christmas, I received this book:  MAKE: Electronics by Charles Platt.  It's a beginner book, with a fair amount of destructive testing, meaning you learn about stuff by playing with it until you have broken it.  I'm a fan.

There is an excellent blog found here that already goes through each experiment in the book, step by step, precisely by the instructions.  I am starting there, and veering off (remember my ADHD?) to other experiments that suggest themselves.  In addition, as I am too much of a cheapskate to actually buy most of the components, I have a 130-in-1 electronics kit that I am using in lieu of dropping around $100 in components.

The first experiment documented here at the Hands On: Make: Electronics Blog (hereafter HO:ME blog, and yes that's an In Living Color reference) involves licking a battery.  Yes, you read that correctly.

(No tongues were harmed in the creation of this image)

A 9V battery, just to give that extra zing.  For those who have tried it, it is relatively easy to feel the current pass through the tongue.  Having prior experience in the realms of neuroscience, my question was:  just how sensitive is the (moist) tongue to current?

This may seem like a silly question.  In fact, it probably is.  However, there is an entire field of study called "electrogustometry" which you may or may not want to Google.  Per Google Scholar, in excess of 1000 papers have been published in peer-reviewed scientific journals on this topic.  So someone out there cares.

Here is the setup:

In the bottom left corner is the 9V battery.  This is wired through the 470 kohm resistor, then in series with a potentiometer (meaning, a variable resistor) that varies from 1.3 ohms up to 45 kohms.  It then runs through a switch (that light blue thing in the lower right corner) and then there are the two yellow wires you can see above, that run to the tongue.

Resistance of the tongue was about 140 kohms the day of the experiment.  There is quite a bit of variability in this measurement, as previously I have recorded as high as 650 kohms, using the same meter, in the same location on the tongue.  Perhaps I had something salty to eat this morning.

This means that the total resistance through the entire circuit that day was 650 kohms, and plugging that into Ohm's law gives V/R=I, or 9.72/650,000 = 1.4 x 10^-5 amps, or 14 microAmps.  Not much, but (just barely) within the detection limit of my meter.  Even if I can feel this clearly, increasing the resistance (lowering the current) doesn't make much sense as it goes below the detection threshold of  my meter.

Nonetheless, I hooked everything up, set the potentiometer to max resistance, and put the wires on the tongue.  I could just barely feel the faintest tickle of current, most apparent when I was tapping them on the tongue.  I did notice an odd phenomena, however, which bears mention.

Not knowing the proper way to measure current with a multimeter, I put the probes in the two springs surrounding the switch above.  This does allow for measurement of current but bypasses the switch and closes the circuit.  When I did so, I had a current of about 17-18 microAmps. When I pressed the switch, the current dropped to 0.1 microAmps.  I was able to detect both, but obviously the stronger current produced the stronger sensation.  I had calculated previously that the resistance through my multimeter is about 4 ohms; across the switch it's about 0.4 ohms.  It's unclear to me why the current dropped when I added another resistor (the multimeter) in parallel.  Perhaps my EE brother can weigh in on the situation.

Reviewing the literature (see comment about electrogustometry above) is an exercise in frustration.
Every relevant paper is hidden behind a firewall, and if you wish, you can pay $31.50 per article to view:

This is, in my opinion, ridiculous.  Your little article is not worth $30.  In fact, it's probably barely worth the paper it's printed on.  Paying for articles also has the effect of dampening scientific research in less-developed countries, as they cannot afford to pay the money to keep up to date with the literature.  Nor can individual investigators (hobbyists) keep up if everything costs so much.  I don't wear tinfoil hats, but this seems like a great way to ensure that the vast majority of research is carefully funneled into official channels, where The Powers That Be can have oversight.  I hate the stupid publishers that think this is a good idea, and applaud journals like PLOS that make everything open source from the start.

::descends from soapbox::

Either way, from the crumbs I was able to glean, they referred to 5 microAmps as a "very high stimulus".  I could feel 0.1 microAmps, an order of magnitude less.  So I am in the ballpark.  They also indicated that the size of the probe itself affects sensation--the larger the probe, the easier to feel the electricity.

Overall a successful experiment.

1 comment:

Steven Deshazer said...

Remember, you always have to put your multimeter in series with the CURRENT you want to measure and in parallel with the VOLTAGE you want to measure. If you try to measure the current by putting your meter in parallel with it, then you have just given current another path to flow and diverted it away from your main circuit (meaning you effectively have no idea how much current is flowing through the circuit in question).
-The (currently) REAL Tx Deshazer ;)