i want to insert L.E.Ds in my arm ..,
i was playing around with the idea of inserting leds in my arm and hooking them up to a wireless battery. what do u guys think about it
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Creating a LED implant that lights up when inside an RFID reader field is pretty easy. Adding a battery also adds quite a bit of complexity, aside from the fact that LEDs eat energy for breakfast.
0 # 0 = 12:15
Besides the clock encoder you'd also need the circuits for keeping the time, adjusting it, a backup battery for the clock, and since led's eat a lot of power you want a decently sized battery for driving those aswell.
Implementing it with a small microcontroller instead saves a lot of components and board space and will most likely have a lower power demand.
And you can very well work with just 8 pins, by arranging the 2 led's in antiparallel between each two pins. Since your eye is very lazy you can cycle through the led's to light one by one. The tristate output of a microcontroller will allow you to target one specific led at a time. You can drive a lot more than 16 led's from 8 output pins.
But then, the microcontroller is the least critical component. A stable clock source and a wireless interface to set the time and of course the battery charging/management are the more difficult parts to get right.
As for setting the time, I'm very unsure on how to do that. I don't want to sacrifice a lot of space for a wireless "shield" (well, the ~ components), but the clock will definitely desynchronize. As the error should be rather minor a "set clock to 0:00" function would be enough. Did anyone ever implant a button or something like that? Would be hard to balance between accidental triggers and too much pressure...
"is there any IC that basically acts as an "if (a&b) ... else ..."?"
Yes. What you're looking for is a digital demultiplexer. For a 2-to-1 demux, if the control pin is HIGH, then it will output one of the input pins; otherwise, it will output the other one. Just hook an AND gate to the control pin and you've got the logic that you requested.
As @ThomasEgi pointed out, though, just use a uc with charlieplexed LEDs for most of your logic. Personally, for something involving that many power-consuming LEDs, I would go with one of the low-power uc's available, like the MSP430 that texas instruments makes (Actually, there are also software solutions to help mitigate the power consumption of the LEDs; in particular, you can make the LEDs blink with a high frequency, so that it reduces the power somewhat but is invisible to the human eye).
One option for transmitting both power and data is the qi standard, and they even seem to make ICs designed specifically for that purpose.
Also, i don't see a need for even lower power microcontrollers. An atmega running on a 32~kHz clock crystal should have an active current demand of about 30μA which is about the same as the average li-battery's self discharge. And if you put it in idle mode for most of the time, you can save another 80% of that. The LEDs eat so much power that saving the few μA on the microcontroller doesn't do much. If you want to save power, it'd be better to switch away from the led's and use electrode outputs instead.
1. a square pcb may not be what you want in your skin. A circle or octagon may be the better choice, or even better, placing the led's on thin strips of flexible pcb.
2. those traces are all over the place at all sorts of angles. try keeping it at 0 45 90° angles for your own convenience.
3. by slightly rearranging the parts you could save a number of vias.
4. the charlieplexing is the only part that comes with no technical challenges. You should iron out the power supply issue first.
3: the bottom and top vias. you could simply rotate led's 9-10 and 3-4 instead of doing a 2via hop to go below them.
The via on R4 ond the U1 marker could be avoided by changing pins on the μC.
The vias on the left and right mid could be connected via a wire running along the outer edge.
It may be easier to use a few extra pins on the μC to get nicer traces, instead of going fubar with traces all over the place. Given the pins would otherwise be unused anyway.
Via's are potential points of failures. Especially when the pcb gets heated and cooled repeated those things can fail due to cracks or even pcb delamination. So avoiding them if possible is a good idea