EasyDriver 4.x stepper controller A3967 ICs are easily fried if, for example, the motor is disconnected while the board is powered. For that matter, loose connectors, dodgy wires and anything that is likely to generate a voltage spike, exceeding the rating of the IC.
This miniature arrangement of diodes is a simple layer of protection and follows the recommendation for this series of boards. Of course, power should always be removed from the board and motor, if applicable, before connecting or disconnecting the motor.
The protection board was hard tested with no overheating smoke or small explosions from the IC. An old well used EasyDriver survived hotplugging the motor, simulating faulty connectors and broken wires and pulling and connecting the power supply, live.
The images show the board layout and design around the EasyDriver 4.x board with access to other through holes, mounting holes and other components.
The protection board may be mounted on or off the EasyDriver board.
A prototype has been in use for a few months now, with no issues. I have surplus boards and diodes, if anyone is interested. Happy to run another batch if there is enough interest.
EDIT: I test the serviceability of all 8 diodes and the board's continuity after soldering, just prior to hard testing. There is no shortcut. No one wants to risk their hardware to an untested add on. The video illustrates the effectiveness of the board in use. Never do this to your ED.
EDIT:
Video demonstration
