LIS2DH12 FIFO interrupt battery consumption on the latest firmware

Hi there,
I’ve recently posted a question about how to enable FIFO interrupt on the latest firmware.

Then, following @otso’s suggestions, I’ve managed to make it work.

Currently, I’m trying to compare the battery consumption of FIFO interrupts on the latest firmware with an older version of the Ruuvitag firmware, using Nordic Power Profiler Kit.

The older firmware was set to transmit a BLE advertisement every 10 seconds. Additionally, the accelerometer’s sampling rate was set to 50Hz, while the resolution was set to 12 bit. I used the same settings on the latest firmware in order to get a fair comparison.

Here’s a screenshot I took some time ago, using the older firmware:

There are a bunch of peaks at ~4mA which are due to the FIFO interrupt firing every 32/50=0.64 seconds.
The 10mA peak is caused by the BLE advertisement which occurs every 10 seconds.

Here’s another screenshot using the latest firmware (slightly modified in order to change the BLE advertisement interval and the accelerometer’s sampling rate and resolution):

So, it seems that the FIFO interrupt consumption has raised to ~10mA (the ~15mA peak should be due to the BLE advertisement, NFC write and GATT in the heartbeat function), from the ~4mA in the previous screenshot.

I was wondering, is that increase in battery consumption expected or am I missing something? Any help would be greatly appreciated.

The most important value to watch is the average consumption, 26.38 uA vs 30.56 uA.

It’s hard to tell what exactly causes the difference in peak levels. First thing that comes to my mind, are both measurements run on same hardware? RuuviTag B8 has more capacitance onboard for better performance in cold where internal resistance of battery increases.

When the higher capacitance is combined with the inductance of long wires to nRF52 power profiler kit, the peak current is higher. Current peaks smooth out when there’s a drained or cold battery supplying the power.

If the hardware is the same, my guess is that the nRF52 CPU + SPI + LIS2DH12 simply consume higher peak current. I would not be worried about it, since the average has increased only by 4 uA or so.

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Hi @otso,
thanks for your response and sorry for the late reply.

The battery measurement with the older firmware was performed on a Ruuvitag bought in 2018, while the latest firmware was profiled with a Ruuvitag bought a few months ago. I don’t know if the hardware has changed since 2018.

I agree, I was just curious :slight_smile:
Thanks again for the response!

You can verify it by looking under the PCB, there’s golden hardware revision number. My guess by the sales dates is that first is “B6” and second is “B8”. That would explain the peaks.

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Hi @otso,
you’re right, I just checked and indeed the 2018 Ruuvitag has hardware revision number “B6”, while the new one has revision number “B8”. Thanks again for following up!