My doctor tells me I should just run and forget the heart monitor, but I feel compelled to measure everything I do. Likewise I want to measure everything about Carl - how fast he can go, how long can he make a battery charge last, how many charge cycles before I need to change his batteries.
Most of these collected measurements are not used by him or by me, but they answer questions that come into my head when I think about Carl.
For example, when I purchase a new set of NiMH batteries I first put them into a BC-3000 charger in “Refresh” mode, which repeatedly charges and discharges them till a max capacity at 500mA discharge rate is determined. The batteries promise 2000mAh and so far all sets of the Eneloop batteries have delivered on the promise.
Today, sporting his new INA219 I2C current sensor and a logging program I threw together, Carl measured his “playtime”. Playtime for Carl begins when he detects his smart charger has begun to trickle the batteries, and he leaves the charging dock. Playtime ends when Carl detects the eight AA NiMH cell battery repeatedly registers 8.1v. That voltage was chosen to leave about 5% capacity in the cells which is 15-20 minutes of thinking and provides reserve power in case Carl’s first attempt at docking is unsuccessful, he can try a second time.
So, drum roll …
Playtime #3069 1905mAh 19.19Wh 7.8 hours
which means Carl’s Pi3B, GoPiGo3 red board (with Blue status LED and green power LED), speaker, distance sensor, and USB sound adapter, (and INA219 current sensor) were drawing an
average of 244mA at 10v - 2.46W
1905 mAh at 244mA rate is a little higher than I expected, but not unreasonable given that the battery set has not shown any diminished capacity yet even though they have powered 238 discharge/recharge cycles since being installed into Carl.
This is interesting and fun, but actually useless info for Carl and for me - worth the $5 invested.