Recipe

Wire a DC motor to a board safely

Use when: a board's pin must turn a brushed DC motor on and off, in one direction

Goal: a circuit where the pin only signals, the motor's current comes from its own supply, and no spike or sag reaches the board

Taught in Driving motors safely

1. 1

   Take both from the motor's datasheet, or measure the winding's resistance and divide the supply voltage by it.

   Example

   A 6 V motor whose winding measures 4 Ω: stall current about 6/4 = 1.5 A.

   Why: the stall current, not the running current, sizes the supply, the MOSFET and the diode.

2. 2

   A supply that can deliver the stall current, with its negative side wired to the board's GND.

   Example

   A 4 × AA pack (about 6 V) for this small motor, minus to GND.

   Why: the board's own supply would sag, and without the joined ground the gate has no reference.

3. 3

   R_{DS(on)} specified at or below your pin's HIGH, drain-source rating well above the supply, current rating well above stall.

   Example

   On an ESP32-S3: an AO3400A (48 mΩ max at 2.5 V, 30 V); at 1.5 A, P = 1.5^2 \times 0.048 \approx 0.11 W.

   Why: a MOSFET that is only partly on overheats at exactly the moment the motor draws most.

4. 4

   Flyback diode across the motor, cathode to +; bulk capacitor across the supply; gate resistor and pull-down.

   Example

   A 1N5819 across the motor, 470 μF rated 16 V across the 6 V supply, 100 Ω gate resistor, 100 kΩ pull-down.

   Why: each part covers one failure: kickback, supply sag, gate current pulses, and a floating gate at boot.