If my maths is right, based on this Wikipedia article[1] a typical lemon or potato battery will deliver about 1mW.
That's not enough to drive even the smallest 32 bit CPU (eg the Cortex M0). Or to be more accurate, you could drive the CPU at ~ 100 Hz from your potato, assuming you had no other hardware.
If you want to play with a tiny, cheap 32 bit board that does not run Linux, but is a lot of fun anyway, I recommend the Freescale Freedom board FRDM-KL26Z (under £13/$20 each -- they're so cheap that one unit didn't reach the minimum order value of the reseller so I had to buy two of them :-).
> That's not enough to drive even the smallest 32 bit CPU (eg the Cortex M0).
Last I heard, low-power Cortex-M chips were running at 100-200µA/MHz, with supply voltages in the 1.8-2.0V range. So you might (barely) have a chance of getting it running on a potato or two, especially if you use sleep modes aggressively. And just because MCU alone is bit boring you could throw in a Sharp Memory LCD (or eInk stuff) too, those are also well below .5mW power consumption.
Of course that would still be far cry from a linux system, but on the other hand it is running on a potato.
That's not enough to drive even the smallest 32 bit CPU (eg the Cortex M0). Or to be more accurate, you could drive the CPU at ~ 100 Hz from your potato, assuming you had no other hardware.
If you want to play with a tiny, cheap 32 bit board that does not run Linux, but is a lot of fun anyway, I recommend the Freescale Freedom board FRDM-KL26Z (under £13/$20 each -- they're so cheap that one unit didn't reach the minimum order value of the reseller so I had to buy two of them :-).
[1] https://en.wikipedia.org/wiki/Lemon_battery