And the winner is....

A project log for GameBoy Zero, but smaller!!

My attempt to get the smallest, simplest GameBoy style device, based on the pi Zero

mooseprmoosepr 04/08/2017 at 20:063 Comments

So all the playing with batteries, and i had yet to test the actual battery i had intended in the first place. My first ever project was run from a 2500mah li-po, which yielded a 10 hour runtime, however was rather large.

So i tried what i thought was a 400mah drone battery, which size wise is smaller than the 2xAA battery holder. These 'pouch' cells come in varoius shapes and sizes, and a bit of hunting can find something perfectly sized

So i fired up the same pico-8 Dank Tombs demo which lets you ramp up the cpu load and let it run. Amazingly we managed to get to the 3 hour mark!!!! This was awesome for a 400mah battery, so i thought i had better check the capacity

that is a trifle high for a 400mah cell. So i looked back at my ebay purchases and apparently it is supposed to be 650mah!! so it is way off!! some quick napkin math will tell us the draw of the pi

527mah / 3 hours = 175.66666666666666666666666666666

so lets call it a 176mah draw!! impressive!!


so after reading the comment by DaveDarko i realize my glaring mistake!! I had not taken into account that my meter is calculating the power being fed into the circuit @ 5V rather than what the battery is probably receiving @ 4.2v

if we therefore take the figures on the display to calculate the wattage the battery charging consumed

5.15V * 0.527A = 2.70878 watts

if we then divide this by the battery voltage, we should in theory get the actual amps the battery got. now if im honest, im unsure here. I would normally assume the battery voltage is 3.7V as this is generally the average number used for li-po batteries. this would give us

2.70878 watts / 3.7V = 0.7321027027027027 or 732mah (thats high!!)

my reservations are due to the fact that the battery actually gets fed 4.2v to get it charged (i know it is not quite that simple) so in theory we could plug 4.2v into our calculation

2.70878 watts / 4.2V = 0.644947619047619 or 645mah (looks more like it!)

so if we assume i am correct, and we are using the 4.2V in the calculations, then we have a different power consumption

645mah / 3 hours = 215mah consumption. still pretty impressive really


davedarko wrote 04/10/2017 at 22:53 point

that's 527mAh on 5.14V right?
so USB5V  / LIPO4V * 527mAh would be around 658 mAh for the actual battery, if you crudely calculate from wattage and back?

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moosepr wrote 04/11/2017 at 08:55 point

ah good catch!!! i just assumed the cheap batteries were generally under capacity, and completely ignored the voltage difference. I will update my post :)

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oshpark wrote 04/10/2017 at 22:20 point

interesting analysis, thanks for sharing!

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