SMA Solar readout

This is the first post of a 3-part series about reading out an SMA solar inverter over Bluetooth and displaying some readings every few seconds. Long-time readers may remember the Solar at last weblog post from several years ago and the SMA Relay, based on a JeeNode v6. The Bluetooth readout code was derived from Stuart Pittaway’s Nanode SMA PV Monitor code.

SMA Solar readout

This project is for a friend who’s birthday is coming up shortly, and who has the same SMA 5000TL inverter as I do – although it can probably be used with other models.

Here is the gadget, powered off 5V USB:

There’s no RF relay in this unit, although I may build a second one for use at JeeLabs, with an RFM69 instead of the LCD.

There are many sides to this project, i.e.

  • µC choice: I’ll be using a low-cost STM32F103 board from AliExpress
  • 2×16 character LCD, which is a bit old-school, but hey, it works…
  • Bluetooth: I’ve selected a simple “HC05” unit, from eBay
  • actual hardware connections
  • talking to BT via the 2nd UART
  • packet protocol encoding/decoding
  • setting up permanent BT pairing
  • formatted number display
  • enabling the hardware watchdog
  • automatic start on power-up
  • a 3D-printed enclosure

The STM32F103C8 board in this unit is this one, but a Blue Pill would work just as well:

There’s a micro-USB socket on the bottom, but it can only be used for power (doh!) – the USB pins do not seem to be connected. So a USB-to-serial adapter will have to be used during development – no big deal.

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