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VK5DJ

Remote power management of a remote amateur repeater site

The Raspberry Pi 2W is a very inexpensive computer on a board. It has a dual core RP2350 microprocessor,2.4GHz WIFI and Bluetooth 5.2, a 150MHz clock speed, 520kB of SRAM and 4MB of on board flash memory. It has a full speed USB 1.1 host/device controller and 26 GPIO pins.

With ideas from the “Geoffg.net” Watering system controller project featured in August 2023 Silicon Chip Magazine I have created a wifi server that allows remote monitoring of the voltage and current of both the loads and the solar charger at The Bluff, site of VK5RMG. This repeater system is the centre of the South East Radio Group’s repeater network covering the Lower South East of South Australia and into SW Victoria.

Using an INA226 board readily available from many Internet shops to measure the readings from a shunt resistor we are able to monitor the load (a 2m voice repeater, a 70cm C4FM repeater, three UHF links to other sites, Echolink, and a packet radio system supporting APRS and a Marine tracking system) plus solar.

The critical part is the software and it depends on “MMBASIC for the Picomite”. This software provides for the establishment of a WIFI connection, a TCP server, TELNET service and USB.

Under normal ‘computer’ operation the Rpi PICO is provided with power and MMBASIC. However in this project I access the WIFI functions and use I2C to access the INA226 board that enables the shunt to be read for current and voltage (up to 36V). It’s a natty little board and comes with its own shunt resistor for twenty amps. However our current can be above 20A (maybe up to 25A peak) so I have made use of a commercial 0.0025 ohm shunt resistor.

The example to the right shows a typical readout with false numbers as it was taken without the INA226 board connected.

Normally it refreshes every 2 minutes and the ‘Previous’ lists previous 6AM, 9AM, Noon, 3PM, 6PM and 9PM readings.

The shunt to the left is a 30 A device that provides 75mV at 30A for detection  by the INA226. At 15A it provides 37mV etc. This has negligible impact on the voltage drop. The load current at VK5RMG currently peaks at about 20ish amps. The INA226 outputs via I2C.