5 ms·
A basic low-power microprocessor (like the MSP430) will run at 1MIPS at about 0.5mA. (Less when sleeping.) At 3V, that's 1.5mW. A Sharp epaper display, like on
by david-given 10y ago
A basic low-power microprocessor (like the MSP430) will run at 1MIPS at about 0.5mA. (Less when sleeping.) At 3V, that's 1.5mW. A Sharp epaper display, like on the Pebble, consumes basically nil when not changing, although I can't find data on energy use when updating. A traditional STN LCD uses about 1mW.
So I reckon it's plausible, just --- thermoelectric generators have traditionally been really inefficient, and I don't know whether getting 2.5mW of electricity out of 85mW of heat is possible. Particularly if you're like me and wear the watch quite loosely.
Edit: Datasheet: http://www.ti.com/lit/ds/slase54a/slase54a.pdf http://www.ti.com/lit/ds/slase54a/slase54a.pdf
That's an FRAM model with non-volatile RAM, so it can power down completely without losing memory. It claims it'll sleep with the clock on at 450nA. (That's nano, not milli.) It also claims it'll run with the processor on at 120 µA/MHz, so the 1 MIPS figure I quoted above must be about 4MHz. I've never run one below that but I gather they'll go down to about 500kHz. Enabling peripherals costs more, of course, but you can leave them powered off until you want to use them.
So, yeah. Totally plausible.
- skykooler 10y agoMost smartwatches are also paired with phones. So there's extra power usage for bluetooth, too.
- rasz_pl 10y agoThere is no epaper in pebble. You can get ~25 microwatts per cm2 per K temp difference (according to Linear). Enough for the Sharp memory display and simple clock circuit.
- fisherjeff 10y agoYeah, it's the screen I'm curious about. The renders on their Indiegogo page make the screen look pretty awesome. FWIW, the original Pebble is rated at 2.8 mW and the Pebble Time is 4.6 mW.
- nom 10y agoThere are CPUs out there with sleep currents well below 0.1 mA, for example the Microchip nanoWatt XLP. The product page advertises 9 nA in a best case sceneario.
- david-given 10y agoWell, the MSP430 sleeps at about 1µA --- below if you turn the clock off! But as you're not really getting anything done when the processor's not asleep, I quoted the power consumption when running. (Of course it's possible to use a capacitor to soak up energy and then run the processor at higher currents, in burst. You'd probably want to do this if you want radio. But on average, you're still getting about the same amount of work done.)
- nickff 10y agoSlight digression, but the MSP430 is obsolete; modern low power ARM microcontrollers are superior in every dimension.[1] [1] I have worked on products with both uC, and the company where I work buys both by the reel and tray.
- david-given 10y agoWould those be the new Atmel SAM L21? I see a reference to 35 µA/MHz and 200 nA sleep mode: http://www.atmel.com/products/microcontrollers/arm/sam-l.aspx http://www.atmel.com/products/microcontrollers/arm/sam-l.asp... So: (a) yay! super low power processors! Bet you can run these off a couple of long wires and radio scavanging; (b) ARMs are so dull. [sad face] The MSP430 is a lovely processor to write machine code for. ARMs are just... dull. Anyway, thanks for the suggestion. I think the MSP430s have a monopoly on FRAM, which makes a vast difference in usability, but I'll check these out.
- nickff 10y agoThe low power Kinetis processor can run at low speed for 32 µA, and down to 1.7 V. Many of the ARM manufacturers produce similar parts.
- deleted 10y ago[deleted]
- nom 10y agoInteresting. Is it still able to wake up regularly without an external source to trigger the interrupt? Or does it have a timer with a dedicated oscillator / clock for that purpose?