3D-printed threaded screw — the squeezer arm rides down the threads, turning motor spin into a linear push.
DC motor
DC motor — drives the screw via the TB6612FNG driver.
Raspberry Pi Pico
Raspberry Pi Pico (MicroPython) — the controller I built & coded.
Dual-channel motor driver
TB6612FNG dual-channel motor driver — runs the motor fwd/reverse.
Keyhole wall-mount slots
Keyhole wall-mount slots — mounts on a bathroom wall.
THE PROBLEM
Conditions like arthritis and Parkinson's make squeezing a toothpaste tube painful or impossible. At the same time, over a third of children routinely use far too much toothpaste — there's no feedback on how much is "right."
Our goal: make correct dosing effortless, hands-free, and accessible to anyone — from a six-year-old to someone with limited hand dexterity.
HOW IT WORKS
The dispenser mounts on the wall. A toothpaste tube slots in from the top; a 3D-printed threaded screw and squeezer arm sit against the tube body. Press the Start button — the Pico reads the current dose setting, commands the motor driver at full PWM, and the screw turns, pushing the arm downward for exactly the right duration. Motor stops. Toothpaste dispensed.
A clear front door lets you see the remaining tube at a glance. Two keyhole slots on the rear mount to standard bathroom wall screws — no special hardware needed.
CONTROLS & FIRMWARE
Button 2 dispenses. Button 1 configures — a single click toggles adult (0.5 s) vs child (0.25 s) mode; a double-click within 600 ms reverses the motor to retract the arm for tube reloading, no disassembly needed. All button reads use 25 ms software debounce polling — no interrupts required.
MICROPYTHON · DISPENSER LOGIC
AdultDuration = 0.5 # pea-sized dose
ChildDuration = 0.25 # rice-sized dose
def motor_forward(duration):
ain1.value(1); ain2.value(0) # set direction
pwma.duty_u16(MotorDuty) # full power
time.sleep(duration) # run for dose time
motor_stop() # then stop
def start_mechanism(): # start → dispense
motor_forward(TimeSetting)
MY ROLE VS TEAM
CHRISTOPHER SPARROW
Electronics end-to-end — wiring Pico, TB6612FNG driver, and push-buttons
All MicroPython firmware: dispense logic, dual dose modes, debounce
Double-click detection for motor reversal without disassembly
Clear plexiglass viewing door — my design concept, letting the user see the remaining tube level at a glance
Integration, assembly, and bring-up testing across all three prototypes
Three-iteration prototyping — cardboard → first print → refined final
Clear front door design for tube-level visibility
Project report, technical documentation, and presentation
ITERATION
Three prototypes across the semester. The cardboard mockup settled spatial layout — tube position, button placement, overall form factor. The first 3D print revealed that the squeezer arm geometry needed a tighter thread pitch to apply consistent pressure without slipping. The final build tightened tolerances, repositioned the Pico to clear the motor wiring, and added the wall-mount keyhole slots.
The trickiest integration challenge: synchronising the mechanical arm advance with firmware timing. Too short and the dose is inconsistent; too long and the motor jams. The 0.5 s / 0.25 s values were calibrated empirically across a full tube.
