Why the Battery Numbers Overturn the Range Guess

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

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Ada ADA · CALCULATION AUDIT

Why the Battery Numbers Overturn the Range Guess

A smart beehive monitoring project needs to reach 50 beehives from a gateway about 200 m away — a distance the chapter itself calls an awkward tweener: too far for BLE or Zigbee, overkill for LPWAN. Its own battery-life model then runs Wi-Fi, LoRaWAN, and Zigbee mesh through the same 2000 mAh capacity and 24 reads-a-day workload, each using its own transmit time and sleep current. This audit asks the question that comparison invites: does the 200 m tweener distance actually decide the protocol, or does the daily battery budget settle it first?

Companion to the chapter Protocol Selector Wizard — every number here comes from that chapter.

Ada: The 200 m “tweener” distance makes range look like the deciding factor, but the beehive comparison is really settled by the daily battery budget. Let me re-run each option’s mAh/day from the chapter’s own current and time figures, carrying full precision and rounding only at the end.

  • Wi-Fi transmit: 5 mA x 10 s = 50 mA·s, and 50 / 3600 = 0.013889 mAh per transmission. Over 24 reads: 0.013889 x 24 = 0.333333 mAh/day active. Sleep adds 0.15 mA x 24 h = 3.6 mAh/day. Total 0.333333 + 3.6 = 3.933 mAh/day.
  • LoRaWAN transmit: 6 mA x 2 s = 12 mA·s = 0.003333 mAh; x 24 = 0.08 mAh/day active, plus 0.0015 mA x 24 h = 0.036 mAh/day sleep. Total 0.116 mAh/day.
  • Zigbee mesh: own transmit 9 mA x 0.1 s = 0.9 mA·s = 0.00025 mAh; x 24 = 0.006 mAh/day, relaying for four neighbours adds 0.006 x 4 = 0.024 mAh/day, and sleep adds 0.003 mA x 24 h = 0.072 mAh/day. Total 0.102 mAh/day.

So the chapter’s 3.93, ~0.12, and ~0.10 mAh/day all reproduce exactly. The decisive ratio is 3.933 / 0.102 = 38.6: Wi-Fi burns almost forty times the daily charge of the Zigbee mesh, and its 3.6 mAh sleep floor — not its transmit cost — is what dominates that gap.

The audit conclusion is bounded: the arithmetic confirms battery, not raw range, breaks the tie at 200 m — but only for these illustrative current and duty-cycle figures. Re-measure the real sleep current and per-read radio time on the installed board before treating any years-of-life claim as a site commitment.

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