knob

This was a gift for my two year old nephew. Since he is a fan of lights and buttons, I wanted to make something blinky for him to enjoy. The concept was simple: make a clear box with buttons and lights that would change color and pattern based on the buttons that were pressed.

First, I had to find a clear acrylic box large enough for some LEDs, switches, buttons and a microcontroller. I found this great polycarbonate box from Hammond Manufacturing that seemed to be the right size. Next, I needed to find some buttons that could take a beating. Fortunately, Adafruit sells some translucent arcade buttons in bright colors. The lighting was a no-brainer as I am a huge fan of Adafruit’s addressable LED strips. I also found a glowy on/off switch for the power. Somewhere along the way, I thought it would be a cool idea to add a rotary knob so that he could select different blinking patterns.

The next step was to assemble the pieces and wire everything together. The polycarbonate box was harder to work with than I had hoped. The polycarbonate would discolor if I used the laser cutter, so I found myself drilling all of the holes with a rotary tool. I then added the buttons, knob and on/off switch.

Once all of the bits were together, I had to add a microcontroller to control the button states and light transitions. I decided to go with the Teensy 3 as it was what I had on hand (and I had yet to work with one). Also, Teensy 3 allows all digital pins to be interrupted (as opposed to four on the Teensy 2), which would simplify reading the button state. The other great reason for selecting the Teensy is that it already has an Encoder library, which makes reading the knob state simple.

The code was easy. Interrupts on the arcade buttons would change a variable representing the color. The interrupt for the black button would kick off a rainbow display routine. In the main loop, I polled for changes in the rotary encoder state and transitioned the lights accordingly. When I was finished, there were five main light colors (white, red, yellow, green and blue), one rainbow routine and six possible blink patterns (always on, fade on/off, blink on/off, chasing light, random twinkling lights and alternating lights).

I saved the hardest part for last: power. I wanted something that my nephew couldn’t disturb, so anything outside of the box was out of the question. Regular batteries would require opening the box to change, so I thought something rechargeable would work better. I decided to go with a Lithium Ion battery. Unfortunately, these are generally around 3.7 volts and the LED strips require 5 volts. This meant that I needed to find a way to recharge the battery from the outside and find a way to step up the voltage. Fortunately, SparkFun sells a power cell board that does both. Yay!

I added a power jack to the box and used an old 5 volt AC adapter to supply the charging power. I then connected the power cell board and the battery using this handy tutorial. Fortunately, the charging of the battery seemed to work! Unfortunately, the power cell board only provides 600 milliamps at 5 volts, which is not enough power to run a full meter of the LED strip. Sadly, I had to cut the strip in half. It was still impressive even with just one loop of lights! To make the battery last even longer, I also implemented some of the suggestions for conserving power with the Teensy.

The best part about this toy is that it is fully programmable. As he gets older, I can program new features or games into it. Perhaps one day, I can even teach him to program it himself! 🙂

Here is a short video of the assembled box