measuring battery capacity with an arduino

I needed a couple of AA batteries and found the display at the supermarket where they were all arrayed. Normally when I`m shopping in the supermarket, I tend to look at the price/kg or price/l when comparing similar products. In the case of the batteries, there was no such indicator. Fine, I thought, I`ll work it out myself. I grabbed a few differ
measuring battery capacity with an arduino - schematic

ent makes and scanned the packaging for some measure of their capacity. Nothing. Not a single one of the batteries had any indicator of how much energy they would provide. Instead, they all had terms like PLUS`, SUPER`, ULTRA` and of course had wildly differing prices. So, I decided that it was time for an experiment and bought one pack of every type I could find. My idea was really simple: I would make a circuit that would fully discharge each of the batteries while measuring how much energy it produced (displayed in Joules and in Watt-Hours. I had an Arduino and an LCD panel left over from a different project so I thought I`d make a standalone unit. As the design evolved, I let two additional features creep in: Note: This was never intended to be a scientific instrument to measure how long a battery would power your circuit - it`s designed to provide a relative comparison of different batteries using a similar load. The circuit works by measuring the voltage across a fixed load every second until the voltage drops to less than 0. 2V. For simplicity, I used a resistive load (the original plan was to use a 4. 7R resistor but I didn`t have any high power resistors to hand so I used 4 22R resistors in parallel instead giving me an effective load of 5. 5R. Here`s the final circuit: This case from adafruit ended up being perfect because it already has cutouts and standoffs for the arduino and the LCD. All that was left was to...

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