Experiment 2

Again, dear reader, I refer you to the HO:ME blog for the details of experiment 2.  In short (pun not intended) the point of this experiment is to short out a battery.  Feel the heat, baby!

So I shorted out the 1.5 v AA battery.  Nothing to see, really, so I'll post a random picture here to distract you:

Nice, eh?

The next phase was to short out a fuse.  I bought the collection of automotive fuses from RadioShack, as that was the only one that had a 3 amp fuse.  Unfortunately, 1.62 volts/.8 = 2.02 amps, which I would not predict would blow the 3 amp fuse.  So I just turned right to the 9v, presuming that my calculated 12 amps should take care of business.

Hooked it up.  Watched.  Waited.  No fire, no energy, no nothing.  What?

Checked the battery.  Produced less than 7 volts.  Double what?

This was the same battery I had used for the earlier tests, and at one point I had run the battery through a very small resistor and then through the multimeter, showing 2 amps current.  Left it like that for a while.  Didn't think much of it.  Until I picked that stupid battery up and found it was--what else? hot as blazes.  I got lucky, I did.  Hot batteries have been known to cause some problems.

Dreamliner grounded due to battery fire

Turns out that the above lead to some reading on the difference between battery capacity, current, amp-hours (or watt-hours) and why folks use a stack of 1.5 v batteries to power their remote controlled cars instead of a single 9v.

Voltage for a battery is set by the number of cells, etc internal to the battery.  Capacity is how much energy it can store--like the size of the gas tank in the car.  A battery can then produce a certain number of amp-hours, which is number of amps for a certain amount of time.  A 9v rated at 2 amp-hours can produce 2 amps for 1 hour, 0.5 amps for 4 hours, etc.  This is analogous to the range in your car.

However, just like in the car, speed makes a difference.  The faster the car goes, the more inefficient it is (air resistance increases as a square of the velocity).  Same for batteries.  Running batteries at high current depletes it faster than the rated amp-hours would suggest.

A typical 9v is rated at 0.55 amp-hours, or Ah.  A 1.5 volt AA has 2.4 Ah, almost 4x as much.  So a stack of 6 AAs in series that add up to 9v will last much longer, at the cost of increased weight.

My 9v would only be expected to run 2 amps for about 15 minutes.  But that's a high current for a 9V, so probably even less.  Its ability to put out the number of amps required to burn out the fuse was clearly compromised.

So experiment 2 was a bust (or not, depending on how you view the fuse).  But good learning.

Follow up to lesson 1 of MAKE: Electronics

So, dear reader, a few follow-ups.

I measured the resistance of the tongue after water, then after a mild salt solution, seen below:

and found no difference in resistance.  I was unwilling to go "more salty" in the name of science.  Today.

My little brother commented that you have to measure current in series, and voltage in parallel.  So the question I had earlier about why the current dropped when I added another element in parallel reflects my igg-ner-unse of how things work.

Ah well.  His electrical kung fu looks like this:

Mine, like this:

'Nuff said.

The setup below was reprised, and instead of pushing the key I just measured across the leads, putting the multimeter in series as it should be:

complete with the 9V battery.  The measured resistance of the tongue today was about 320 kohms.
So the resistance du jour was around 835 kohms, and with the battery consistently putting out about 9.7 volts, that predicts around 11 microAmps.

Measured amps across the tongue was in the range of 14 microAmps.  Given the literature I read, I was expecting a threshold around 1 microAmp, perhaps lower.  Need More Resistance!

Turns out that to get down to 1 microAmp (an order of magnitude drop from 10 microAmps) I need an order of magnitude more resistance.  9.7 Mohms, to be precise.  I don't have enough resistors to do that, even if I wire them all in series I barely cross 1 Mohm.  So we downgraded the battery to AA and 1.56 volts.

So Mr. Ohm predicts 1.8 microAmps with this approach, and indeed we were in the ballpark.  Turns out my threshold is somewhere just shy of 2 microAmps.  Turns out in my previous experiment that when I was pushing the switch that "connected" the circuit, I wasn't actually changing the current, despite a change in the multimeter reading.  More on that later.

So Experiment 1, subexperiment 1 is done.  Threshold: around 1.8 microAmps.

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.

Occasionally, I'm just too embarrassed to tell the wife...

So, my youngest son likes to sit on a particular heating vent in the corner of his room.

He loves this thing.  He will sit or stand on it, warming the pertinent body part, especially in the morning when it's a bit cold in his room and we are trying to get the other kids ready for school.

This morning, of course, our rather sick 2 year old is sitting in his favorite spot when he overflows his diaper with diarrhea.  A rather neutral colored, light tan, with small to moderate chunks, should you care to know (this becomes important later).  Katie found him with "stuff" running down his bum and--you guessed it--into the vent.

So I am called in my manly capacity of "corrector of all things house-related" to clean up the poo in the vent.  Fortunately, there is a short segment of ductwork that runs horizontally before a vertical shaft drops directly into the main airshaft, allowing localization of what could have been a whole-house catastrophe.

A few paper towels later I have most of it cleaned up.  I call the oldest boy to bring a flashlight so that I can evaluate need for further cleanup.  As you can see in the picture above, this vent is in the corner of the room and not exceptionally well-lit.  So you really have to crank your way around this thing, and get very low to the carpet, to see in it.

As I am peering into the poorly lit but highly odiferous hole, I note with initial dismay a cool/wet sensation on my forehead as it touches the carpet just on the wall side of the hole.  Dead center, right at the hairline, in point of fact.

For those who have not seen me in a while, "right at the hairline" is likely further north than you are currently thinking.

So I sit up with a dime sized spot of poo that nearly perfectly matches the color of the carpet centered in the above named area on my head.  And for once, I am thankful that "right at the hairline" represents considerably more distance than it did in days of yore.

I am additionally thankful for the entire roll of paper towels situated conveniently near my side.  And for the fact that the wife and kids left soon after, enabling the second shower of the day.

At times I am convinced that my wife thinks I am just this side of completely incompetent when it comes to household chores.  And I just could not bear adding further evidence to the "loser" side of the balance sheet this morning. Now that sufficient time, soap, shampoo, and sundry other cleaning agents have been successfully applied, I am feeling more confident.

Hope your day has gone better than mine, dear reader.

Can only read 10 papers per day...

I am trying to prep for two talks on back-to-back days I have to give next week.  I have read about 5 or 6 papers, with still a few to go, and my brain is tired.  So I decided to post something here so that my brain will not explode.  (It's very messy, the exploding).  Then I'll get back to work.

I have a long-time but little-attended hobby of hand-tool woodworking.  One of the key elements of same is the employment of hand planes, such as this example below:

No, I do not own this plane.  It's called a "coffin smoother" and is likely in the range of $3000.

I own this:

Which is a cheap Stanley block plane that probably doesn't cost $25.   And it's not in the greatest shape.

Those in the know will recognize both rust and an uneven sole, which really messes with your woodworking.  Although not pictured, the blade itself was chipped, uneven, etc. 

So, I decided one day, randomly, to sharpen the blade as the first step in the restoration of the above plane.  This step was chosen, as I don't actually own what I need to do any of the other steps.  

I used a Veritas honing guide as well as a pack of 3M sandpaper on glass (the so-called Scary Sharp method). 

Results?  I grabbed a rough cut yard stake to test.  The pic on the right shows the initial surface, very rough; that on the left, the upper surface, post-planing.  An attempt is made in the bottom pic to show the contrast between the two.  Not bad.

And just to give a feel for what I was taking off, if you look closely in this picture at the shavings I removed, you can see the individual wood fibers.  This shaving is right at 0.003 of an inch.

All in all, a lot of fun, and gratifying to know that you don't need $200 toys to play this game.

Now, back to ECMO.

Sickening

Not sure who the rat bastard was who decided it was "cool and stuff" to walk into a kindergarten class and shoot his mom (by report) and all of the kids in her class.   Just sickening.  What kind of culture produces this insanity?

Bet your bottom dollar I'll be giving the little ones a big hug tonight.  The wife too.  Life is so, so precious.

2

This little guy is 2 years old today. Oh, how the time flies!!