RAK12035 soil moisture sensor high current

Hi everyone,
I started testing soil sensor RAK12035 in tandem with RAK4631 for a new application and I noticed that sensor draw current even with sensor off (3V3 supply off).

During MCU sleep and sensor powered off I read 3.15mA @ 3.7V. With sensor disconnected consumption drop to 150uA.

The two pull-up resistors on I2C bus should not pull that much current.
Any thoughts?

Thank you

Welcome back to forum @carlacda .

Regarding the soil sensor current, can you please check if the supply if it is 3.3V during ON time then 0V during sleep/power saving?


Thanks for your quick reply.

I confirm that during mcu sleep and when sensor.sleep() is called, voltage drop from 3.3 to about 0.

I have tried to disconnect the sensor whilst in sleep and current suddenly drops from 3.15mA to 100uA.
I checked the two I2C wires (in sleep mode) and I found them at 0.127V with sensor connected and 3.3V when disconnected.

Additionally, I have tried to give wire.end() command to disconnect I2C bus once communication is completed but it remains pulled up to rail at 3.3V.


Not sure what code you are using, but did you try to use the sensor_sleep() and sensor_on() functions.
This old example of mine LPWAN-Soil-Moisture-Solution does not use WB_IO2 to shut down the sensor, instead it is using only sensor_sleep() and sensor_on().
I can’t remember clearly (it was 2 years ago), but I think there is a current leak problem with the MCU on the sensor when you use WB_IO2.

Hello Bernd,
I do use Arduino BSP with command sensor_on() and sensor_sleep().

I tried to add a schottky diode on the 3V3 to the sensor and current dropped to 200uA.
The diode presented a reverse voltage of 2.5V while sleeping. Since I removed the two 10k pull-up resistors for troubleshooting, I’m wondering if the I2C bus leaks through the MCU.


just an update.
I was able to bring the total current MCU+Sensor to 83uA by adding 3 N-chan mosfet on SCL, SDA and RESET and all three gates controlled by 3V3_S.

This for me is satisfactory since 99.9% of the current is from the MCU now.

Would be good having similar update directly on-board of RAK12035.

Thank you for your input

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