Launchpad takes ultra low power to the extreme

We’ve all known the MSP430s under the Launchpad are designed to be low power, but who wants to bet how long the chip can last on only 20F worth of capacitors? A couple of hours? A day at max? [Kenneth Finnegan] setup a MSP430 with supercaps to find out. To make sure the chip is actually running, [Kenneth] programmed it to count from 0 to 9 over a period of 10 seconds, and then reset. To get it ultra low power, the chip is in sleep mode most of the time, and a raw low current LCD is used to display the output. While [Kenneth] simply checks the chip every few hours to see if it’s still counting, a setup much like the Flash Destroyer, tracking a clock and then storing the current value would get a more exact time of death. Either way, it’s been over 3 weeks…and still counting. Video after the rift.

Comments

  1. j s says:

    I’d like to see Seiko Epson’s offering when it comes out. They have virtually unrivaled experience in the development of ultra low power chips. Their ULV processor technology is behind the regulator in Seiko Spring Drive watches.

  2. WestfW says:

    > (i_sleep * %_sleeping) + (current_wake * %_awake) = i_total.
    It’s nowhere near that simple anymore. N different sleep modes, M different clocks for different parts of the chip, individually powerable peripherals; the complexity goes on an on.
    For example, TI claims that their chips “wake up” so much faster than most micros that this results in significant power savings…

  3. WestfW says:

    @DB: guess what? A capacitor is a fine tool for doing that integration for you, which is why this sort of setup is very useful for measuring circuits with low current consumption.

    v(t) = 1/C * integral(T0, T, i(t) dt) + v(T0)

    So if you accurately know the initial voltage and the current voltage on the cap, that will tell you the average current consumption over the time period involved. (Well, “C” is usually not well known, but if you’re doing the comparison between two different parts, the actual value will cancel out.

    Alas, things have gotten so good that I suspect most such contests will end with the firmware folk going back and saying “I can get it lower!” or the HW folk looking for better non-ionic cleaners for the PCB. When fingerprints start being a significant power loss, things have gotten pretty crazy…

  4. Myke says:

    rcx: “specifically, 20F at 2.7V will store 20 x 2.7^2 = 145.8 coulombs. a 1000 mAh battery will store 1000 x10^-3 x 3600 = 3600 coulombs, or 25 times as much.”
    Wrong, wrong, wrong. 20F * 2.7V (NOT squared) = 7.40C

  5. Myke says:

    God, now I feel stupid. I now noticed I actually divided instead of multiplying… That would actually be 54C.

  6. Well… I think this comment thread helps justify why I decided that just running it would be the most effective measurement.

  7. Aged Cheddar says:

    @ Kenneth Finnegan – Amen to that.

  8. will says:

    honestly, lets stop fighting over whose right or wrong and see the results of how long it lasted, then hook up the 2 caps to an arduino and count how many seconds it lasts

  9. Casey O'Donnell says:

    @will that would be awesome

  10. @Ken – If you would have just done math, and made a video of you writing it all out on a whiteboard… everyone would just be saying “oh, but don’t forget about the leakage current” and “oh you’re so stupid because you calculated the charge, assuming you could ever really fully charge those caps” and “I already tested this on Microchip’s XLP series micros and they’ll totally PWN your MSP!”

    What you did was what most normal people would do, an experiment to see WTF really happens. Rock on Ken, I know you’ve opened some eyes with your demonstration. I’m sorry but people don’t have the patience for boring posts involving math… just show us the results! Then after you’ve sucked us in with results, go ahead and show us all of the little bits that make it work – if you want. Or we can just read all of the attempts at calculating something here in the comments… although nothing I read tells me as much as your video.

  11. xiaolong says:

    Hi All,

    I got another question. What brands or model of LCD used? The LCD able to power up even if the V capacitor drop until 1.6v? What is the minimum voltage and current needed for the LCD ? Thank you very much.

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