Arduino Project 9 uses a pushbutton to switch a small motor on and off. The Arduino controls an IRF520 MOSFET, which switches a separate 9V motor circuit; a diode protects the transistor from voltage produced as the motor slows. You’ll need the circuit components, an Arduino, and a paper-and-CD spinner.
Parts you need
The official Project 9 parts list includes these circuit components:
- 10-kilohm resistor
- Momentary pushbutton
- Motor
- 9V battery
- IRF520 MOSFET
- 1N4007 diode
You also need an Arduino board, breadboard, jumper wires, battery snap, CD hub, CD, and the project’s die-cut paper pattern. The maintained Arduino example lists the same core Project 9 components and identifies pin 2 for the switch and pin 9 for the motor control. Arduino’s Project 9 example and the Arduino Projects Book are the relevant project references. [c001][c002]
How the circuit works
The pushbutton connects to digital pin 2. A 10-kilohm pull-down resistor connects the input to ground when the button is released, giving the Arduino a LOW reading instead of leaving the input floating. The sketch sets pin 2 as an input and pin 9 as an output. When pin 2 reads HIGH, the sketch sets pin 9 HIGH; the MOSFET then completes the motor’s separate 9V circuit. When the button is released, pin 9 goes LOW and the motor is switched off. [c001]
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Wire the motor and 9V battery through the MOSFET as shown in the project circuit, and connect the battery ground to Arduino ground. The shared ground gives the control signal a common reference. Connect the 1N4007 diode in parallel with the motor: its anode goes toward motor ground and its cathode toward motor power. Check the MOSFET’s pinout against the exact component you have rather than assuming its legs match a diagram for a different part. [c001]
Build the circuit and spinner
- With power disconnected, place the pushbutton and 10-kilohm resistor on the breadboard. Wire the switch output to Arduino digital pin 2, and wire the pull-down resistor between that input and ground.
- Connect Arduino pin 9 to the IRF520 control pin. Wire the MOSFET into the motor’s 9V circuit, then connect the battery ground and Arduino ground together.
- Place the 1N4007 diode across the motor, with its anode toward motor ground and cathode toward motor power. Confirm the battery path, MOSFET pinout, and diode orientation before connecting power.
- Assemble the CD hub, attach the paper pattern to the CD, snap the CD onto the hub, and secure it with a drop of glue.
- Power the Arduino over USB and attach the 9V battery snap. Press the breadboard button to run the motor.
Keep the spinner securely attached, and keep faces and eyes away while it rotates: the project manual warns that a loose rotating piece can fly off and cause injury. You can change the paper pattern to create different visual effects. [c001]
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Project 9 sketch
The sketch’s behavior is a direct switch: a pressed button makes the motor-control output HIGH; a released button makes it LOW.
const int switchPin = 2;
const int motorPin = 9;
void setup() {
pinMode(switchPin, INPUT);
pinMode(motorPin, OUTPUT);
}
void loop() {
if (digitalRead(switchPin) == HIGH) {
digitalWrite(motorPin, HIGH);
} else {
digitalWrite(motorPin, LOW);
}
}This is the control logic described for Project 9: the transistor activates when the output is HIGH, completing the motor circuit; when the output is LOW, the motor is not driven. [c001][c002]
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Troubleshoot a motor that won’t stop or start
If the motor runs continuously
- Check that the switch output is actually connected to pin 2, not a neighboring breadboard row or Arduino pin.
- Verify that the 10-kilohm resistor pulls pin 2 to ground when the button is released.
- Confirm the IRF520’s control and switching pins match the part’s actual pinout.
- Make sure the 9V battery ground and Arduino ground are connected together.
If the motor does not run
- Check the 9V battery, battery snap, and wiring through the motor and MOSFET.
- Confirm Arduino pin 9 reaches the MOSFET control pin.
- Check that the motor circuit is continuous and that the motor is connected correctly.
- Verify diode orientation: anode toward motor ground, cathode toward motor power.
These checks follow the documented circuit connections; they are not a report of hands-on testing.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why Project 9 includes a diode
A motor does not stop instantly when power is removed. As it coasts down, it generates voltage in the opposite direction, which the project manual calls “back-voltage.” That voltage can damage the transistor. The diode across the motor provides a safer path for it, so it is a functional protection component—not an optional decoration. [c001]
Quick Recap
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