Let's make a wireless 3D drawing stylus!

This project was a collaboration with Madeline Gannon.

This stylus can be used to trigger object tracking on our motion capture system. Using a capacitive sensing circuit, we can send a message via Virtual Serial to Processing (or any other software that has access to serial) to begin recording the Stylus' position when the tip comes in contact with the skin.

Additionally, we can use a button to tell the system to trigger the recording without needing to touch the skin.

To track the stylus, you need a motion capture system. In our case it's an Optitrack.

Download the Arduino and Processing code, we'll use this later.

I've also included a copy of our BT Stylus_v2.stl if you want to 3D print it.

Step 1: Ingredients

Here's the list:

Lightblue Bean by Punchthrough Design
3.7 V, 150 mah lipo battery (you can also use a coin cell, but this will last longer)
a random metal tip
a metal strip
momentary push button
switch
1k ohm resistor
1M ohm resistor
various soldering wires (solid core)

Step 2: Capacitive Circuit: Tip

Solder the 1M ohm resistor to pins 0 and 1.

Then solder the a wire between the resistor and pin 1.

Step 3: Power

To get some more life out of the circuit, we're gonna add a 3.7 V 150mah Lipo battery.

To do this we need to solder some wires to GND and BATT pins.

Step 4: Capacitive Circuit: Ground

Now let's add the ground for our capacitive circuit.

Take the metal strip and solder it to the other GND on the Bean.
Then, solder the 1k ohm resistor from the metal strip to pin 5.

Step 5: Add Switch

Add the switch. Adding the switch is good for battery life :))

Step 6: Add Momentary Push Button

Let's add a nice switch to the circuit.

Solder one leg to the VCC to give it power.
Solder the GND leg between the 1k ohm resistor and pin 5 (shown here as the yellow wire).

*Make sure you're using the correct legs on the switch, some switches have a NC leg (normally closed) and a NO leg (normally open), we want to use NC (normally closed). The middle leg is usually common (ground).