Ada Audits the Measured State Ledger
Ada recomputes the charge ledger, average current, and pack lifetime from the measured states
ADA · CALCULATION AUDIT
Ada Audits the Measured State Ledger
The chapter measures a node’s cycle: a WiFi burst of 150 mA for 1.5 s (225 mA-s), a short sense at 40 mA, and deep sleep at 12 uA — averaging 0.395 mA for about 211 days on a 2000 mAh pack. The radio burst alone is 94.9% of the cycle charge. This audit recomputes the measured state ledger to show why shortening association beats tuning the tiny sleep term.
Companion to the chapter Lab: Energy Measurement — every number here comes from that chapter.
A battery estimate is an area-under-the-current-curve problem. The chapter's measured states already give current and time, so the review can recompute the charge ledger instead of trusting the summary.
1. Convert every state into the same unit
Deep sleep is stated as 12 uA, so it must become 0.012 mA before multiplying by seconds.
| Review item | Arithmetic shown | Decision signal |
| WiFi associate + TX | 150 mA x 1.5 s = 225 mA-s |
This is the dominant state in the measured cycle. |
| Wake + sense | 40 mA x 0.12 s = 4.8 mA-s |
The current is high, but the duration is short. |
| Deep sleep | 0.012 mA x 598.4 s = 7.1808 mA-s |
Long duration does not dominate when the current floor is truly low. |
| Cycle total and average | 225 + 4.8 + 7.1808 = 236.9808 mA-s; 236.9808 / 600 = 0.394968 mA |
Rounded at the end, the chapter's 0.395 mA average is verified. |
| Pack lifetime | 2000 mAh / 0.394968 mA = 5063.7 h; 5063.7 / 24 = 211.0 days |
The battery estimate follows from the measured average current. |
| Association improvement | 150 mA x 0.5 s = 75 mA-s; 75 + 4.8 + 7.1808 = 86.9808 mA-s; 86.9808 / 600 = 0.144968 mA |
The proposed static-IP-style reduction gives about 0.394968 / 0.144968 = 2.72x improvement. |
| Board sleep-floor failure | 10 mA x 598.4 s = 5984 mA-s; 5984 + 225 + 4.8 = 6213.8 mA-s; 6213.8 / 600 = 10.356 mA |
A board-level sleep floor moves lifetime to 2000 / 10.356 = 193.1 h, about 8 days. |
2. The physics conclusion is state dominance, not peak current alone
The verified ledger says the radio burst is about 225 / 236.9808 = 94.9% of the cycle charge. That is why shortening association beats tuning the already-small sleep term on the bare module.
3. The claim is bounded to this measured trace
A different board, regulator, radio attach time, reporting interval, or battery capacity must be recomputed from its own measured state ledger.
Every number above is taken from this chapter's own worked example and re-derived step by step.