Ada’s Calculation Audit: Ten-Minute State Budget

Ada re-derives this chapter’s own numbers step by step, at full precision

ADA · CALCULATION AUDIT

Ada's Calculation Audit: Ten-Minute State Budget

The chapter’s ten-minute cycle spends 599 s asleep at 10 uA, 0.7 s of active work at 20 mA, and 0.3 s of radio at 120 mA — totalling 55.99 mA-s, an average of about 93 uA. The radio supplies 64.3% of the charge while occupying just 0.05% of the cycle. This audit works the ten-minute state budget to show short high-current states can dominate charge, yet long sleep still earns real savings.

Companion to the chapter Power Consumption Analysis — every number here comes from that chapter.

Use the chapter’s measured ten-minute cycle. Convert every state to the same unit, multiply current by time, and divide by the full cycle length only at the end.

Formula

State charge = current x duration.

Average current = total charge / cycle time.

• Sleep: 10 uA = 0.010 mA, so 0.010 mA x 599 s = 5.99 mA-s.
• Active work: 20 mA x 0.7 s = 14.0 mA-s.
• Radio: 120 mA x 0.3 s = 36.0 mA-s.
• Total charge: 5.99 + 14.0 + 36.0 = 55.99 mA-s.
• Average current: 55.99 mA-s / 600 s = 0.0933167 mA, so the report cycle averages about 93.3 uA.
• Radio share: 36.0 / 55.99 = 0.643, so the radio contributes about 64.3% of the charge while occupying 0.3 / 600 = 0.0005, or 0.05%, of the cycle time.
• Active-current improvement: 5 mA x 0.7 s = 3.5 mA-s saved, which lowers the average by 3.5 / 600 = 0.005833 mA, or 5.83 uA.
• Sleep-baseline improvement: 3 uA = 0.003 mA, so 0.003 mA x 599 s = 1.797 mA-s saved, which lowers the average by 1.797 / 600 = 0.002995 mA, or about 3.00 uA.

The physics point is the time integral: short high-current states can dominate charge, but long sleep states still earn real savings when they span almost the whole cycle.

Every number above is taken from the chapter’s own material and re-derived step by step.