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JEJunior Engineer LabPico W + micro:bit course
11 60 minutes

Tabletop mask mechanism

Capstone: a light paper flap that opens and closes at the press of a button

Tabletop mask mechanism project
Illustration of the finished idea. Build from the diagram and connection table, not the photo.

Mission goal: Combine servo, button and LED into a calibrated tabletop mechanism that moves a light paper flap smoothly between two endpoints, toggled by one debounced press.

Section 1

Understand

New ideas

  • Calibrating endpoints for your own mechanism
  • Moving in small steps instead of jumping
  • A toggle that cannot be retriggered by holding
  • Honest limits: no position feedback, no emergency stop input
  • 1One button press opens or closes a light paper flap.
  • 2The servo moves in small steps; the LED shows the commanded state.
  • 3Tabletop paper only. Cutting motor power is the emergency stop.

Safety first

  • The servo must be powered from an external REGULATED 5 V supply able to deliver at least 1 A, with a suitable insulated connector. That supply may be an extra purchase beyond the kit, and an adult must check it before it is used.
  • Never power a servo from a GPIO pin or from the 3V3 OUT pin. A servo pulls far more current than those pins can give, and trying it can damage the board.
  • The external supply's positive wire connects to NO Pico pin at all. Not VBUS, not VSYS, not 3V3. The Pico stays powered from the USB cable.
  • The only thing shared between the two power systems is ground: the external supply's 0 V connects to Pico GND at physical pin 38. Without that shared ground the servo cannot understand the signal.
  • Secure the servo to something solid, such as taping it to a heavy book, before powering it. A loose servo whips around.
  • Test with the horn removed, or at least with nothing attached to it. The very first command can make the servo jump suddenly to a new position.
  • Actual lead markings on your servo override any colour convention. Red is usually positive and brown or black is usually ground, but check the printed markings or the supplier's documentation.
  • If the servo buzzes continuously, gets hot, or is clearly straining against something, cut the motor power immediately.
  • Switch BOTH the USB power and the external supply off before any rewiring, and before fitting or removing the horn.
  • Light PAPER FLAP only. No wearing, no heavy printed faceplate, no mounting on a head or body.
  • Calibrate with the servo unloaded and the flap off, before anything is attached.
  • Both power sources off before fitting the flap, fitting the horn, or any rewiring.
  • There is no electronic emergency stop in this design. Keep the external supply switch within reach; cutting motor power is the immediate stop.
  • The program cannot see a button press while the flap is moving. Do not rely on the button to stop a movement.