2.8 Test MOSFET Output

Check List · Step 8 of 12 · Test GPIO.4 and GPIO.5 MOSFET outputs with M7 / M8 / M9

🎯 Objective

The board has two MOSFET outputs, io.4-MOS-GND and io.5-MOS-GND. The V5.77 test YAML assigns GPIO.4 to mist coolant (M7) and GPIO.5 to flood coolant (M8); M9 turns both off. Confirm each channel across its two-pin terminal with a multimeter.

🔌 How it works: each output is a low-side MOSFET. The pin name io.4-MOS-GND tells you it is the GND side that output io.4 switches. In normal use your load wires between Vmot-Main (+) and io.X-MOS-GND; turning the output ON connects io.X-MOS-GND to GND, so the full motor voltage (Vmot, ~24 V) appears across the load. With no load attached, the multimeter reads that voltage straight across the two terminal pins — about 0 V when off, ~24 V when on. Maximum current is 1.5 A per channel. For heavier loads, use an external relay or suitable power driver; overloading can burn the MOSFET.
V5.77 Carrier board: the two orange MOSFET output terminals (io.4-MOS-GND / Vmot-Main and io.5-MOS-GND / Vmot-Main) and their GPIO.4 / GPIO.5 indicator LEDs
The two MOSFET terminals (right, orange) — each has an io.X-MOS-GND pin (top) and a Vmot-Main pin (bottom) — and their indicator LEDs (red circle, GPIO.4 / GPIO.5). (click to enlarge)
🔧 How to Measure

Set the multimeter to DC voltage, auto-range. On the orange io.4-MOS-GND terminal, put the probes across its two pins — top pin and bottom pin, exactly as in the photo:

RED (+) → Vmot-Main (bottom) BLACK (−) → io.4-MOS-GND (top)

With nothing switched on it reads about 0 V. (If the meter shows a minus sign, your probes are reversed — just swap them.)

io.4-MOS-GND (−) black Vmot-Main (+) red DC V 24.0 Multimeter (DC V)
GPIO.4 — io.4-MOS-GND terminal
M7 → 24.0 VGPIO.4 LED on
M9 → 0.0 VLED off
👈 Now move both probes to the io.5-MOS-GND terminal — same way: RED (+) on Vmot-Main (bottom), BLACK (−) on io.5-MOS-GND (top).
GPIO.5 — io.5-MOS-GND terminal
M8 → 24.0 VGPIO.5 LED on
M9 → 0.0 VLED off
✅ Pass: each terminal reads approximately the VIN Main supply voltage when its command is on and returns to about 0 V after M9. The GPIO.4 / GPIO.5 indicator LED should follow the command.
⚠ Careful: Vmot-Main carries the full 12-24 V supply. Do not let the probe tips touch each other. Use an external relay or power driver for larger loads, and verify load polarity before connection.
Step 8 of 12 2.9 Test PWM Output →