4.3 Connect External Relay

Use the MOSFET terminals or an isolated logic-level interface

Do not route mains voltage through the controller board. The V5.77 only supplies control signals. Keep mains wiring inside a rated enclosure and use a correctly rated relay, contactor, or SSR.

Preferred: Drive a 12-24 V DC Relay Coil

Choose a relay coil whose voltage matches VIN Main.
Connect coil positive to Vmot-Main and coil negative to io.4-MOS-GND or io.5-MOS-GND.
The onboard flyback diode protects a correctly polarized inductive load. Verify polarity before power-on.
In the test YAML, use M7 for GPIO.4, M8 for GPIO.5, and M9 to turn both off.

Logic-level Relay / SSR Interface

You may instead use GPIO.4/GPIO.5 on the PWM 5 V header or one of the six reserved I2SO outputs. The interface input must accept the selected 3.3/5 V level and must not overload the logic pin. An optically isolated PiBot IsoSwitch or equivalent interface is recommended where electrical isolation is needed.

GPIO.4 and GPIO.5 feed both their header pins and their onboard MOSFET channels, so these are not independent functions.

Acceptance check: test without a mains load first. The relay changes state exactly once per command and returns to the safe/off state after reset or alarm according to your machine configuration.

Next: 4.4 Connect Pendant →