SolarNode "Howler Monkey" meter support

"Howler Monkey" is a Raspberry Pi-based device with an integrated ATM90E36 energy meter chip.

meter-tool script

The meter-tool.py Python program is a CLI tool for reading and calibrating the ATM90E36 chip.

OS setup

SPI communication must be enabled in /boot/firmware/config.txt by adding a line with dtparam=spi=on.

Then to allow SolarNode to access the SPI devices, add solar to the spi group:

# add solar to spi group
usermod -a -G spi solar

Reboot the device after making these changes:

sudo reboot

Software setup

The software requires the spidev Python package, which requires a working compiler on the device. Install the necessary compiler support and set up a Python virtual environment for the packages:

# install python + pip + venv support + spidev compile support
sudo apt install python3-pip python3-venv python3-dev

# install build support (for spidev)
sudo apt install build-essential libtool

# setup venv
python3 -m venv ~/python/venv/hm
source ~/python/venv/hm/bin/activate
pip3 install spidev

Copy the meter-tool.py script to the device. Make it executable:

chmod 755 meter-tool.py

Run tool

Run the tool without any options to print out CSV data on a continuous loop (hit Ctrl-C to stop):

# run tool (prints CSV to STDOUT)
./meter-tool.py

Timestamp,Voltage_A,Voltage_B,Voltage_C,Current_A,Current_B,Current_C,Power_A,Power_B,Power_C,Power_Total,PF_Total,Frequency
2026-09-09 03:42:50,654.27,0.00,0.00,65.427,0.000,0.000,-2264.96,0.00,0.00,0.00,0.000,0.00
2026-09-09 03:42:55,654.27,0.00,0.00,65.427,0.000,0.000,-2264.96,0.00,0.00,0.00,0.000,0.00

Calibration mode

Run the tool with --mode calibrate to configure the meter settings:

./meter-tool.py --mode calibrate

============================================================
ATM90E36 Calibration Mode
============================================================

Device initializing...

============================================================
CALIBRATION MENU
============================================================
1. Show current measurements
2. Voltage calibration
3. Current calibration (Phase A)
4. Show calibration values
0. Exit

Your choice (0-4):