The radio is the expensive part
🎯You'll be able to
Reduce radio energy by sending less often, batching, keeping connections short, and choosing the right radio.
🏠The everyday picture
Driving to the market for each item on a list costs far more fuel than one trip with the whole list. Starting the car is the costly part.
📘What it really is
-
Joining is costly: joining a Wi-Fi network can take a second or more at over 100 mA. Sending a small message after joining is quick.
-
Batch: collect several readings and send them together. JalSetu reads every 15 minutes and sends once an hour.
- Send at once when it matters: an alarm (a low tank) goes immediately; routine readings wait.
- Send less: only readings that changed, plus a heartbeat (IO8).
- Keep connections short: connect, send, disconnect, turn the radio off.
- Choose the radio: Wi-Fi is fast but power-hungry; LoRa and NB-IoT reach far with little power but send little data; Bluetooth Low Energy suits short range to a phone.
📝A worked example
Input: the starter joins Wi-Fi on every wake.
Steps:
- One join: about 1.2 s × (30 + 130) mA ≈ 190 mAs, plus sending.
- Every wake: 96 joins a day ≈ 18,000 mAs; every 4th wake: 24 joins ≈ 4,600 mAs.
- Battery life improves by roughly three times from this change alone.
Expected output: Project 1's test 7 (send every 4th wake, or at once for an alarm).
🌍Where it's used
- Fitness bands sync to the phone a few times a day, not every heartbeat.
- Smart meters send daily totals rather than every reading.
- Asset trackers send more often only when moving.
📝Case scenario
A farm sensor sent every reading as soon as it was taken. Batteries lasted a month. Sending every hour, with frost alarms sent at once, made them last a season, and farmers still got frost warnings in time.
🖱️Try it
Using the kit's currents, work out the daily charge for joining Wi-Fi every wake, every 2nd, every 4th and every 8th. Success: four figures and the battery life for each.
⚠️Common mistakes
- Sending every reading at once. Sign: the radio dominates the budget. Fix: batch.
- Delaying alarms with routine data. Sign: late warnings. Fix: alarms skip the queue.
- Staying connected. Sign: Wi-Fi idle current all day. Fix: disconnect and turn the radio off.
🛠️For your project
Project 1's test 7 checks the send schedule; Project 2's test 9 checks edge filtering.
✅Quick check
Why does batching readings save so much energy?
Show the answer
Joining the network is the costly part, so fewer joins save most.
Which readings should skip the batch?
Show the answer
Alarms, such as a low tank, which matter straight away.