The random labinator indicated that I should be prepared to show a creative application of the labs from the first week. I also took this as an opportunity to practice documentation.

Below, you'll see how you too can use a LEGO minifigure as a switch to activate a bubble machine! The Arduino is only used to provide power, but this would be an easy circuit to integrate with a microcontroller.


  • bubble machine toy (including battery pack)
  • LEGO minifigure
  • transistor
  • resistor*
  • diode
  • 5V power source
  • wire, gaffer tape, zip ties

How It Works

1. Bubble Machine

I found this bubble machine at Toys 'R' Us for $10 bucks. It's just been sitting around on my desk.









2. Dismantle bubble machine & remove switch

This device had super annoying triangle shaped screws. I ended up destroying them with the wrong screwdriver.

Inside, there is a battery pack with 6 AA batteries attached in series (9V) with a ceramic capacitor & switch.

3. Set up the circuit.

I decided to use a transistor to activate the bubble machine. This allows an interface between the 9V of the machine motor and 5V Arduino system. As an analog circuit, this isn't necessarily required in this instance; however, it will be helpful when the switch and motor are integrated with the microcontroller.

I experienced some confusion trying to figure out what resistor to use between the switch and the transistor. I found with a 2.2K transistor, the motor didn't run at full speed. Some experimentation resulted in me connecting two resistors and eventually using a 220 Ω resistor.

An important note: for the circuit to work, the ground of the battery pack and Arduino power bus must be shared. I missed this at first, and my circuit didn't work!

Here is the circuit layout:

4. Testing

I used a game console push button to test the system before I built my own switch.

5. Build the magnifying glass bubble blower

I've found it's really hard to work on the LEGO scale. I ended up making a loop of copper wire and using a zip tie to attach it to the bubble blower to make the first switch contact.

6. Build the LEGO minifigure face contact 

The wrapped copper wire around the head of the minifigure wasn't staying in place. I decided to cut a hole in the side of the head and make a small grove to hold the wire in front of the face. 

7. Rewiring the battery pack 

I soldered longer wires on the battery pack. Using solder wick I removed excess solder that was on the battery contact. Solder wick gets very hot! So it's a good idea to use pliers or another tool to hold onto it. 

9. Final circuit 

Once everything was soldered and happy, I checked over the circuit. Transistor: check. Diode: check. Success!

9. Done

Not really a step!










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