The as-built schematic, such as it is:
Yes, the SSR negative output goes to the Protoneer + Power Input.
I should drive the SSR from the
Motor Enable output (in the external motor control header), rather than +5 V, to let GRBL control the motors, with a manual E-Stop override. The A4988 drivers require
-Controlinput (replaces GND)
- +5 V to BRS to SSR
+Controlinput (as before)
The SSR Control input draws 13 mA at 5 V, suggesting I should drive the AC SSR (for the spindle motor) from the DC SSR output, rather than paralleling the two on a single Arduino output pin.
I can attest to its effect on rational thought; a molly-guard may be required.