IntermediateRobotics and Motion
Stepper Motor Dial Controller
Drive a small unipolar stepper through a ULN2003 driver and move it with two direction buttons.
Parts from the database
- ULN2003ADR × 1Darlington array; use on a suitable driver board
- Raspberry-Pi-Pico × 1Microcontroller
Other supplies
- 28BYJ-48 5 V geared stepper motor with matching ULN2003 driver moduleCommon build supply
- two pushbuttonsCommon build supply
- 5 V motor supply sized for the motorCommon build supply
- Pico boardCommon build supply
- jumper wiresCommon build supply
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Connections
- Use a matched 28BYJ-48/ULN2003 module. Connect its IN1–IN4 to Pico GP2–GP5 and GND to Pico GND.
- Power motor VCC from a separate 5 V supply; join supply ground to Pico ground.
- Buttons connect GP14 and GP15 to GND; use internal pull-ups.
- Never drive the motor coils directly from Pico GPIO.
Build steps
- Check the exact driver module pin labels and motor connector orientation.
- Upload a slow stepping test and verify the motor turns without skipping.
- Add buttons for clockwise/counterclockwise motion and adjust step delay to suit the load.
- Mount a paper pointer only after the rotation direction and end-stop behavior are understood.
Software and firmware setup
Firmware is required, but a complete button-controlled sketch is not included yet. The Pico must run an Arduino-compatible core. Use four output pins in a repeating four-phase sequence for the ULN2003 inputs, and read the two direction buttons with INPUT_PULLUP. Start with a slow step interval and stop if the motor stalls or heats.
Test your build
The shaft should rotate smoothly in both directions at a conservative speed. The 28BYJ-48 has gearing and backlash, so it is not a precision positioning stage.
Troubleshooting
- If it vibrates but does not rotate, check coil sequence and the motor connector.
- If the Pico resets, improve separate motor power and shared ground.
- If torque is weak, reduce speed and make sure the 5 V supply is adequate.
Safety and limitations
Keep fingers clear of gears and use a low-voltage motor supply. Do not stall the motor for long periods.
Manufacturer and platform documentation
Community Notes for This Project
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