Proposed hardware components
Hi everyone,
since the Southpaw space is pretty much empty, i figured it would be nice to set up a list where we collect parts which may be used for the device.
for all parts suggested it would be good to have:
-Short describtion (like 3axis digital compas with I²C interface)
-Part Number
-Reason why you think it would be suited (maybe pointing out advantages over previously suggested parts)
-Link to the datasheet
-available packing options (x y z dimensions + pincount , because size matters)
-estimated power-consumtion for operation and idle (because we most likely run on some kind of battery)
-a supplier to buy the part from (maybe one for the bare part, one for the part on a breadboard for easier prototyping)
-anything else that seems relevant, like number of external parts required for operation.
so i'll start with some core components:
Atmega8HVA Microcontroller
-well known microcontroller, good crossplatform toolchain, widely used, low power, ADC and I²C to interface with analog/digital compass, lithium-battery-management buildin, 1.8 - 9 V operation range. plenty IO ports.
-available in tsop 28 (1x8x14mm ) and LGA 36 (0.5x3.5x6.5mm)
-draws 800µA under normal operation @ 1MHz , 270µA idle, 25µA powersave
-listed at digikey but currently not in stock ~6$
-no external parts needed. can provide a 3.3V output (with automatic linear-down or step-up with very few external parts). LGA packing may be hard to solder by hand but first choice when keeping size down.
HMC5843 3-axis Digital compass with I²C interface
- i²c interface so no mesing with analog stuff, connects nicely to the atmega, 2.5-3.3V
- 16 pin LCC (4x4x1.3 mm)
- draws 160µA when sampling at 2 Hz
- breakout boards and chips available at digikey for about ~20$
- requires 2 capacitors: 0.22µF and 4.7µF , 2 pullup resistors required for i²c (may be possible to use atmega's internal but that needs to be checked)
VL-3032 Rechargeable Lithium Battery
- 100mAh capacity , 3V, 4mA charge current , small encapsuled coin-cell, Ø27x3.5mm, easy to solder, integrates well with the atmeg's li-battery management.
- 5 days of operation for 1000µA load, 15 days for 300µA . recommended continous load : 200µA
- using this battery requires agressive power-saving on the controller/compass. only allows "slow" charging.
additions and improvements are highly welcome.
small addition: Attiny 85V would also do great, it can be clocked significanntly slower which means.. a lot less power, has a smaller footprint. it lacks the battery management functions, but those can re-implemented easily. and.. .it's available for purchase and a lot easier to solder.
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Comments
So, as a pretext: my knowledge is about one year old, when I had a course of neurobiology including some experiments with an earthworm and some locusts. With the earthworm we actually induced signals (electronically) and recorded the reaction (as I remembered today..) when with the locusts we were only recording.
I can't find my protocolls, but will look for them. Right now I read about the current that is necessary to induce a single ap (http://en.wikipedia.org/wiki/Action_potential). You can also see it here: http://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Action_potential_vert.png/300px-Action_potential_vert.png
it is about 20 mV. (using dc works just fine)
One short peak for about 2 miliseconds is enough (for what I remember)
However you have to consider getting through the skin and other tissue. Plus: you don't only want one ap but some more in a row. But as said earlier: I will read up about the details of the experimments with the earthworm, as soon as I find them.
As for the electrodes: we were using some aluminium foil or something compareable. Can't really be sure about the kind of metal, but I think it was aluminium. Not, that it matters. We put the earthworm on the foil and put a current on it. The other pole of the dc was ground, for what I recall now.
What that means for Southpaw: as mentioned in the comments a simple uncoated
loop of metal (platinum is bioproof) should suffice.
Again, this should be tested thoroughly for the details... For one, because Lepht is not a worm and we not only care about her safety, no, we want to spare her pain and she actually could tell us if something really hurt...
If I had the equipment (or access to the lab once again...) I would test it myself, but I don't so, I just write down how I would do it (and how it SHOULD work) so if anyone got what is necessary...
Best place for this test are the fingertips, basically because they got a lot of nerves. So they are easier to hit even though there is skin in between. Then start with a small current of 20mV dc. Turn the power on and off and see what it feels like. Then put the current up by steps of 5 (or if there is no feeling at all 10 to 15)mV. Also small variations in duration are possible. Also variations in the setup (both poles on the skin, variants in the distance between them, only one pole and the other one is grounded, such stuff). I mean even if in the original there was only one pole, we have to get both of them inside the skin...
This really should be safe (dc plus very small currents), however I suggest only someone knowing what he (/she/it) is doing should do it. There are mistakes, such as choosing the wrong current (pain) or the wrong electricity (ac, could cause serious injuries).
As I said, as soon as I know the original setup I will be able to provide further information, but the electrodes themselves won't be a problem. They are just some bioproof metal.
Ben
Just found some of the recordings and we used WAY higher currents. 3V and higher. Plus I remember having seen a bet of someone testing 12V batteries by touching them with his tounge (though I still would not recommend that. Won't harm, but hurt a litte)
Sry, I will have to find the instructions, as soon as I remember where I put them...
Not too sure about the dc now either, as I remember touching batteries and not getting shocked...
How much was that TENS?
Trust me, you lick a 12V battery, you will definitely feel it. Hell, it's possible to shock yourself by chewing on aluminium foil, if you have the right dental work.
http://www.masterbond.com/info/specialty-silicone.html?gclid=CKKc67Pyv6YCFcse4QodxWTVGg
I've got a link to some electrode suppliers as well, but it's in the mythical "somewhere." I'll see if I can find it.
(not for the not writing, but for the confusing current and voltage...for not writing as well, of course)
I know quite some people who would slap me if they could read what I wrote there, I couldn't blame them.. It is even in the unit! (V for Voltage)
Anyhow, I couldn't get hold of the instructions from back then and whoever I asked didn''t know the details either. As for the hardware I am almost certain that it was a special signal generator and as such not exactly ment to be sold to private persons (thus rather expensive)
But I do like the using the soundcard as a signal generator!
Tried it putting two small needles in my arm, but ok, didn't really work. Was to be expected... Next time deeper, but first: who exactly did you generate the signal? Especially: how did you determine the voltage comming from the audio signal? Did you just measure it and then more or less try and error? (louder, measure etc)
And the shop looks good, too. One thing, though. As a quick overview, how much do you guys guess this thing will cost? I remember Lepht saying that with electrodes more than the 8 directions would be nice (maybe I imagined some of that statement, in that case lets calculate with 8).
Using this electrode:
E-202
4,0mm dia. x 1,0mm disk, 10mm exposed wire
9,50 €
No critics, just asking.
Also: http://electrodesales.stores.yahoo.net/el450.html 10 needle electrodes for $25. They're huge in length, though.
Any ideas what would assert the interrupt?
I didn't know about that self-interrupt technique; the last interrupt stuff I did that didn't involve a threading library involved 68k assembly and IRQ handlers, so I was focused on it being an external signal.
Samples per second would need to be worked out; how any lag affects perception would be a good question to have answered before locking that. I was kinda assuming around the same; 1 or 2 a second.