The problem

For people with arthritis or Parkinson's, squeezing a toothpaste tube can be painful or even impossible. Kids have the opposite problem. Over a third of them use more toothpaste than they should, because nothing tells them how much is enough.

We wanted to make getting the right amount easy for everyone, from a six-year-old to someone who has trouble using their hands. With our dispenser, it takes one button press.

How it works

The dispenser hangs on the wall, and the toothpaste tube slides in from the top. Inside, a 3D-printed screw and a squeezer arm sit up against the tube.

When you press the Start button, the Raspberry Pi Pico (the small computer that runs everything) checks which dose you picked and runs the motor at full power. The motor turns the screw, which pushes the arm down onto the tube for just the right amount of time. Then the motor stops and your toothpaste comes out.

A clear front door lets you see how much toothpaste is left. Two keyhole slots on the back fit regular bathroom wall screws, so you don't need any special hardware to hang it.

Buttons and code

There are two buttons. The Start button gives you a dose. The Settings button switches between two doses. The adult dose runs the motor for half a second, and the kid dose runs it for a quarter second. If you press Settings twice within 0.6 seconds, the motor runs backward and lifts the arm back up, so you can load a new tube without taking anything apart.

When you press a button, the metal contacts bounce for a split second, so one press can look like several. To fix that, the code checks the buttons in a loop and waits 25 milliseconds to make sure a press is real. This is called debouncing, and doing it this way meant I didn't need interrupts, a more advanced way of reacting to button presses.

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)

Who did what

Three prototypes

We built three prototypes over the semester. The cardboard version helped us figure out the basic layout, like where the tube and buttons should go and how big the whole thing should be. Our first 3D print showed that the screw's threads needed to be closer together so the arm would press evenly without slipping. For the final build, we made the parts fit together more tightly, moved the Pico so it wasn't in the way of the motor wires, and added the keyhole slots for hanging it.

The hardest part was matching how far the arm moves to how long the code runs the motor. If the motor runs too short, you get a different amount every time. If it runs too long, the motor jams. We picked the half-second and quarter-second timings by testing them over an entire tube.

From sketch to final design

Concept sketch

First 3D print

Physical build

Final 3D model

Watch it work