the story behind…
I wanted to be able to control the trickle charge for the starter battery from the house battery's SOC. Also, I wanted to automatically keep the house battery at 60-70% soc for storage mode.
At the end of the day, there are many other options.
I have distributed the ve.direct from the BMV or Smartshunt to an Arduino and in parallel to a USB->ttl adapter similar to the ve.direct to USB. So this should work without any problems with BMV-712 or Smartshunt and any GX device. I tested it with the BMV and Smartshunt on a Raspberry with Venus OS. The ve.direct connection is opto isolated. All power is supplied via the USB-ttl adapter, so there is no hassle with different voltages and or GND. The logical inputs can be expanded as desired, currently the following is implemented: D+ , charge disconnect, load disconnect, 2 on/off.
Today I added the active fan control for an Orion-TR smart, it turns on when D+ is on and off when SOC = 100% or D+ is off.
The whole thing can be easily assembled on a breadboard for 10-20€ with pre assembled parts from Ali.
If anyone is interested I'm happy to share the schematic and arduino sketch
