Let's Powerball (II): DIY Speed Meter

I've bought a Powerball not so long ago and I decided to buy it without the inbuilt digital speed meter. However, a workmate (Richard, a.k.a. the EDLUT designer) has developed his own revolution counter using a coil of enamelled copper wire, an audio cable and a computer with Matlab.

How to do a speed meter (rpm counter) for a regular NSD Powerball:

1. Check that your Powerball has a magnet inside. You only have to put it close enough to another magnet.
2. Look for an unused jack plug (the one used to connect the phones to the computer) with a long wire.
3. Attach the audio cable to the wrist band hole. Leave the majority of the cable at the plug side.
   
4. Make a coil with the enamelled copper wire. Stick it around the top of the Powerball using some tape.
   
5. Strip the audio cable and remove the enamel from the wire. Sold them or join them with some tape. It should look like this.
   
   
6. Connect the jack plug to the microphone hole.
   
7. Lanch the Matlab code and start your Powerball. (You can download it from Sourceforge)
   
   
8. ENJOY!

Use the microphone volume to control the homemade speed meter accuracy and noise.