We tag reusable containers on our line with nRF52832 BLE tags (own firmware, Zephyr) that advertise temperature every 60 s. A Pi gateway near the dock hears them and reports them to Hermetry as child devices on the v1/gw topics.
Two things, possibly related:
1. Measured sleep current is 38-42 uA. Datasheet says around 2 uA with RTC running. At 40 uA the CR2032 lasts maybe 6 months, I promised management two years.
2. In Hermetry the tags flick between online and offline all day. The offline alarm I put on the profile fires constantly, people mute it. The tags are fine, they’re sitting right there.
Could it be the coin cell? Mine read weird when the battery was cold.
Is UART logging still on in the build? On the nRF52 that keeps the high-frequency clock running.
Logging is on, CONFIG_LOG with the UART backend. And on the gateway side, the script sends v1/gw/disconnect for a tag if it hasn’t heard it for 60 s.
Both of those are your problems, I had the same pair on battery water meter tags last year.
Current: the UART peripheral being enabled keeps the HF clock up, that alone is hundreds of uA when active and tens when idle. Set CONFIG_SERIAL=n and CONFIG_LOG=n in the release build (or CONFIG_PM_DEVICE and suspend the UART). Also enable the DC/DC (CONFIG_BOARD_ENABLE_DCDC=y, needs the inductor fitted on your board), and make sure unused GPIOs aren’t floating. That got us from about 35 uA to 3.
Online status: for child devices Hermetry takes the online state from the gateway’s v1/gw/connect and v1/gw/disconnect messages, so your gateway is telling it the tags are gone. With 60 s advertising and a 60 s timeout, one missed advert means a disconnect. Make the gateway wait for 5 missed adverts before sending disconnect.
For the alarm, set the Device offline rule’s Open after to something like 900 seconds so a short gap doesn’t page anyone. More on how child status works: Gateways and devices behind a gateway.
Logging and serial off plus DC/DC: 3.1 uA on the bench. Gateway now waits 5 minutes before disconnect, and the offline rule opens after 15 minutes. Zero offline alarms since Tuesday, and the battery estimate is back over two years.
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