Tea Dispenser

This project has been built in the context of a rapid prototyping class.

It is a structure with a silo and an endless screw, which dispenses what you have put in the reservoir, when it detects a cup underneath. It is designed to dispense bulk tea, but you can put whatever you want in it as long as it fits.You can also enlarge the dimensions of the reservoir and the screw if you want it to dispense something bigger or sugar for example.

• Arduino UNO
• Load cell (example here)
• Stepper motor (example here)
• A switch (example here)
• Breadboard or an arduino shield for the command of the stepper motor (exemple here)
• Depending on your power supply capacities : resistors. We used two 10kOhm resistors.

To begin with, it is best to test all the components one by one to make sure they work properly.

Use simple control libraries to check the stepper motor and the load cell.

Use a multimeter to check the switch and the resistors.

The structure must be rigid and fairly waterproof. It should be able to hold a cup of water, allow the weight of the cup to be lifted with the load cell, and dispense the tea into the cup.

We had access to 3mm MDF sheets and PLA 3D printers.

So we printed the worm gear, dispenser, hinges and load cell base on the 3D printer, and cut the rest of the structure out of the MDF with a laser cutter - which is definitively not the most waterproof material.

The 3D design has been done using CATIA V5.

Pay attention to the tolerance between the parts: between the distributor tube and the screw, for the motor axis (be careful there is a meplat), and between the MDF parts.

The code works like this:

The value of the variable resistor is continuously read. This value is compared to a threshold value, which is chosen a little bit under the value given by the sensor in measuring the weight of a full cup of water. When the value of the sensor exceeds the threshold value, the stepper motor is activated for a given number of steps.

If the switch is already activated before putting down the cup, the motor run as long as the switch is pressed, setting the max number of steps in the process.

Otherwise, if the switch is not pressed when the threshold value is exceeded, the stepper motor is rotated by the fixed number of steps.

Finally, the dispensing can be stopped at any time by pressing the button briefly.

This is where, depending on your power supply capabilities, you may need to regulate the tension with a dedicated module if you're not using an arduino shield and/or don't have the volts to send.

It's also better to use resistors across the load cell and switch to prevent them from drawing too much power.

Be careful to print the dispenser tube in the right direction to avoid printing defects on the inside of the tube: this would prevent the screw from turning and can be hard to cleanup.

You now have a nice tea dispenser. Feel free to change the dimensions, or improve the code.

It would also have been nice to protect the electronic part a bit better, splashes can happen quickly !