The Plant-Pot Energy Budget
Ada re-derives this chapter’s own numbers step by step, at full precision
ADA · CALCULATION AUDIT
The Plant-Pot Energy Budget
Motor duty cycle, sleep current, and rounded battery life, ~4 minutes
A Braitenberg controller can be simple, but the battery claim still needs physics bookkeeping: active motor current, daily duty cycle, and sleep current must all be in the same charge units before the lifetime estimate is trusted.
An IoT plant pot uses two LDRs and two DC motors to rotate toward a window, drawing about 280 mA while active for roughly 5 minutes a day and only 10 µA while asleep the rest of the time. Powered by 2500 mAh AA batteries, the chapter estimates a battery life near 107 days, crediting the motor’s duty cycle rather than the sleep current. This audit asks the question that estimate invites: once the charge ledger is carried through in full, does motor-on time really dominate the plant pot’s battery life?
Companion to the chapter Braitenberg Vehicles: Sensing to Action — every number here comes from that chapter.
The charge ledger
active charge = 280 mA x 0.083333 h = 23.333 mAh/day
sleep current = 10 uA = 0.010 mA
sleep charge = 0.010 mA x 23.916667 h = 0.239 mAh/day
2500 mAh / 23.572 mAh/day = 106.1 days, rounded at the end
The conclusion is unchanged from the quick estimate: motor-on time dominates. Reducing active minutes from 5 to 2 would save more energy than shaving a few microamps from sleep current.
Every number above is taken from the chapter’s own plant-pot energy example and re-derived step by step.