Still waiting on the stepper L298N PCBs but the Raspberry Pi Zero breakout board is behaving correctly; enabling the voltage level converters and signals through to the EasyDriver units.

One area that I've revisited on the break out board is the 5v regulator, when running at 12v input, by my calculations the thermals are at the limit. If I go to 24v supply the discarded power will double, pushing it over the limit, due to the waste heat.

So a warning to others, remember linear regulators dump the difference in input to output voltage as heat, if you have the option, use a switching regulator (which nowadays are pretty cheap to implement with a minimum of components).

I've sent a small board off to OSH for a switching regulator to supplement my existing boards and re-organised the rev A2 breakout board design to use a switching regulator. Annoying, but such is the development process. Other tweaks have been balancing the USB traces from pogo pins to USB connector, removing the power connection to the USB connector. and adding solder pads for the USB connector housing legs.