The old arm PCB was capable of controlling all 7 arm motors and read all current (6 AS5147) sensors. This was good at that moment, but now more sensors are needed.
This is why I have split the electronics into 2 smaller electronics, each capable or controlling 3 stepper motors and reading more sensors.
My initial plan was to place both electronics on shoulder (where the previous electronic board was placed).
But now, I have realized that I can place one of this small electronic on shoulder and the other one on elbow. In this way the length of the cables will be significantly reduced. There are 3 stepper motors, 1 servo, 3 AS5147 and 1 current sensor on the upper arm and all these can be connected to the elbow electronic. Huge reduction on wires and complexity!