With the Arduino software loaded onto the Circuit Playground Classic, your Light Paintbrush will need power and one additional sensor -- a potentiometer -- to control brightness. You'll use the battery holder as both power supply and handle for your Light Paintbrush. This is expedient, inexpensive, and a great example of form following function. You could build a nice enclosure for the project if you like, but the Light Paintbrush works well without one.

The first build step is to attach leads to the potentiometer. The potentiometer uses three connections to the Circuit Playground Express -- ground, signal, and voltage. The ground and voltage are references for the varying resistance of the middle signal leg as the knob is turned. The Circuit Playground reads these changes as analog values from 0 to 1023, which are then remapped to NeoPixel brightness values in the software.

Cut one clip end off of each alligator clip lead, and strip away a bit of insulation to expose the wire. Tin the potentiometer legs with solder, tin the wires, and then solder the wires to the legs in the order shown here.

Then, clip the leads to the pads on the Circuit Playground Express:

• black to GND
• yellow to #10 
• red to 3.3V

Next, use a small piece of foam double-stick tape to connect the battery case to the back of the Circuit Playground.

Finally, use some foam tape to attach the potentiometer to the battery case.

That's it, your Light Paintbrush is complete!

Turn it on and try tilting the brush to change colors, and adjust brightness with the knob.

Now comes the artistic part -- time to make some light paintings!