This battery cell monitor uses the Nordic Semiconductor nRF52840/nRF52833 with MQTT-SN over OpenThread. It is meant to be used for monitoring a Lithium battery cell connected between the VDDH pin and ground on the nRF chip.
Three values are sampled and published on MQTT:
- The voltage on the VDDH pin of the nRF chip
- The internal temperature of the nRF chip
- An external (optional) TMP102 temperature sensor mounted on the battery cell
To identify each battery cell, the device ID is included in the topic. For now the topic to subscribe is "nrfcellmon/{ID}/data". One topic is published containing the device ID ("id"). The battery/cell voltage in mV ("mv"), the battery/cell temperature in degrees Celsius ("tb") and the self/device temperature in degrees Celsius ("ts") in the JSON encoded payload. If the device ID is "E19928773B8398AF", the battery voltage 3779mV, the battery temperature 22°C and the internal temperature 25°C, the published topic looks like this:
nrfcellmon/E19928773B8398AF/data
and the JSON encoded data: { "mv" : 3779, "tb" : 22, "ts" : 25 }
Commands over MQTT
Commands can be sent to each cell moditor using the topic "nrfcellmon/device ID/command"
-
identify
This is used for device identification. When received the four LEDs of the development board are blinked in order.
example "nrfcellmon/E19928773B8398AF/identify"
-
reset
Resets the device by calling NVIC_SystemReset
example "nrfcellmon/E19928773B8398AF/reset"
The project files in this repo use relative paths to the nRF5 SDK. It should build out of the box when cloned in the examples/thread folder of the nRF5 SDK for Thread and Zigbee.
nRF5 SDK for Thread and Zigbee v4.1 and lower does not support using VDDH as input to the SAADC and you need to comment out these lines in the function nrfx_saadc_channel_init in the file modules/nrfx/drivers/src/nrfx_saadc.c to avoid getting an assert:
NRFX_ASSERT((p_config->pin_p <= NRF_SAADC_INPUT_VDD) &&
(p_config->pin_p > NRF_SAADC_INPUT_DISABLED));
NRFX_ASSERT(p_config->pin_n <= NRF_SAADC_INPUT_VDD);