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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  • Search the forum for the terms: inductive power supply.
    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.
  • thanks man i will do .and i was think about using a lithium battery and connecting it to a wireless receiver 
  • edited December 2013
    @Josethehuman What kind of coating are you using?
  • Are there any images or videos of implanted LEDs available? I would like to see  the resulting brightness and color.

    Ideally, I would like to implant an 8-LED watch in my left forearm.
  • S0lll0s thats a great idea .and it would be quite a simple circuit the only problem is size. and  grey knight i was thinking of coating it with a thin layer of liquid silicon 
  • @S01110s:  Videos of implanted LEDs?  Here, and here.  Video quality kind of sucks, but there you go.
  • @Ian: yeah, I saw the circadia, theres a better video in the Vice report. Didn't someone say only orange LEDs worked? For the clock to be precise, I'd need two color-leds.

    It would work like this:
    # - red, 1 = green, 0 = off
    0 0 0   = off
    0    0
    0 0 0

    0 # 0 = 12:15
    0    1
    0 0 0

    0 # 1 = 12:10
    0    1
    0 0 0

    0 # # = 1:40
    1    0
    1 0 0


    I though about the PCB, and I could realize it with 8+1 pins (one per LED and one giving what color, then alternating between red and green leds). That would require two 7000-series AND and two 7000 NAND gates, however a mix of both would be best;

    is there any IC that basically acts as an "if (a&b) ... else ..."?

    like this:
    13 12 11 - 10 9  8
     :    :    :   :   :   :   :
    1   2   3  +  5  6  7

    3 = 1&&2  ;  7 = 5&&6  ; 11 = !(13&&12)  ;   10 = !(9&&8)

    or even like this:

    1   2   +
     :    :    :
    3   4   -
    3 = (1&&2)  ;  4 = !(1&&2)

    ??
    That would solve a lot of wiring issues and scale the board down a lot.
  • @S0lll0s the "if (a&b) ... else ..." would be the AND, or NAND, depending on what polarity you need. But using discrete logic seems like not so much of a good idea. Those chips are rather big and the required low voltage versions are hard to come by.
    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.
  • But you would need 16 pins for LEDs alone, isn't that a bit much for a small microcontroller to handle?

    Also I know it would be ANDs and NANDS, but because of the arrangement it would be cool to have an IC that provides two gates of each in one piece.
  • Even a rather small microcontroller has like 20 to 24 IO ports.

    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.
  • You mean multiplexing them somewhat like this?
  • Yes, even tho it's not exactly multiplexing. The technically correct term would be "Charlieplexing" but the idea behind it is very similar. If you don't mind the wires (and there is no need to since 4 layer pcb's are pretty cheap these days) then you can get your desired led's with just 5 IO pins.
  • Thanks for the heads up, I remember knowing this some time ago ^^

    I have set up a quick 6 LED example with my Arduino uno now, works great.

    Can you recommend any mircocontrollers for something like this? I thought about using an ATMega328 (the flat square version)
  • Going with a TQFP atmega is one of the best options you have. Depending on the additional circuits you have the choice between a variety of atmega products. One of the more interesting versions are include battery protection and charging circuitry, like the atmega 8/16hva.
    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.
  • I thought about having The battery implanted seperately and further back in the arm, where there is more space (lower forearm is very bone-y) and connecting it with wires like the ones you can order at the way page that is floating around somewhere in the wiki.

    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...
  • You could add a short-range wireless transmittion with a small smd coil, a resonating cap and a diode+cap rectifier. With simple it's a very small footprint and can be used for bidirectional communication using OOK and load modulation. On top of it, power can be transfered (at least for a slightly bigger receiver coil, talking about 8x8mm or so. I have a test circuit for it but the pcb is still stuck in customs for like a week now. The power and wireless part fits onto about 10x15mm single-sided (contains no battery management tho). The tests I ran so far got me more than 20mA on a 4.7V limited output.
  • @S0lll0s

    "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.
  • @Ian the Qi standard's data channel is reserved for the charging protocol. The coils and supply circuitry for Qi are pretty big too. For example the texas instruments chip for Qi charging takes about 25 passive components + the tricky to solder IC itself. I'd only recommend Qi for when you have really really high power demands.
    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.
  • saw this, thought it was cool. Probably not what you want, but it might be relevant to the thread in general, as I know some are looking for single LED implants.
  • changing the path of the magnetic flux with a mechanical switch is a pretty interesting concept. I agree that it may not be the right thing to use here, but certainly a clever trick to keep in mind for future designs.
  • Here is what I came up with in Fritzing:

    image

    What do you think? Timing & Power Supply things are obviously missing, I only made the charlieplexing and resistors yet.
  • What I think:
    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.
  • 1. I want to do something like that later, but there are so many parts missing on the PCB that I have to change the size and shape later on anyway.
    2. If Fritzings grid was working, I would've done that, but it doesn't.
    3. Which do you mean? And what are the downsides of vias?
  • 2. maybe you want to use a more capable electronic design suite. While eagle works for most people for small projects. i'd recommend to look into kicad or gEDA.

    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
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