I manage a hotel and I’m building my first LoRaWAN sensor, so apologies for missing obvious things. It’s a temperature sensor for the pool plant room: Arduino Nano, RFM95W module, DS18B20, the MCCI LMIC library, OTAA, EU868. Our LoRaWAN gateway is registered in Hermetry and the sensor is added as an OTAA device. The sketch sends every 10 minutes and sleeps in between with the LowPower library.
On the laptop USB it works for days. The device’s LoRaWAN tab says Joined and readings arrive.
On a 10,000 mAh USB power bank (the plan is to swap it every few weeks) it joins, sends exactly one uplink, and then nothing. The frames log shows the join and one uplink, then silence. When I unplug and replug the power bank it does it again: join, one frame, silence. Device shows offline after a few hours.
Same sketch, same board, only the power source changes. What could the power bank do to the code?
Maybe the power bank voltage is too low? Try a 9 V battery into VIN, that’s what I used on my first Arduino.
A 9 V block won’t last a week with the Nano’s regulator and LED. I’d not go there.
It’s the power bank switching itself off. Had exactly this at our property with a door counter last year.
Most power banks shut their output down when the load drops below somewhere around 50-100 mA for a few seconds, because they think the phone is full. Your Nano draws far more than that while the radio is sending, and a few mA (or less) when LowPower puts it to sleep. So: join, first uplink, sleep, power bank sees almost no current, output off. Nothing for the code to do about it. Replugging restarts the bank.
Ways out, from what we tried:
- Use a power source without that feature: 3 x AA alkaline straight to the 5 V pin is ok for a Nano (4.5 V) for a while, or better a LiPo with a decent low-quiescent regulator. A bare Pro Mini at 3.3 V with the power LED removed runs for months on AAs.
- Some power banks have an “always on” or low-current mode, usually a double press of the button. Check the manual.
- Dummy loads that pull pulses to keep the bank awake work, but they waste most of the battery.
Also adjust Hermetry so it matches the sensor. On the built-in LoRaWAN profile the device counts as online while the last uplink is younger than three expected intervals, with 3,600 s as the default interval. At one uplink per 10 minutes you’re fine, but if you stretch it to hourly or longer to save battery, raise the expected interval on the profile’s Online status tab, otherwise it flips to offline between reports. That bit is in Troubleshooting uplinks and downlinks.
Thank you emily! You were right, I measured it: the bank cuts out about 30 seconds after the first uplink. Mine has no always-on mode, so I moved to 3 x AA on the 5 V pin and took the LED off. It has sent 140 uplinks since yesterday. Next step is a Pro Mini like you said.
ok, never mind the 9 V idea then 😅
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