Crayola Kidsball to Opti-PAC

For my rotating design to work, I wanted to keep the number of cables coming out of the panels to a bare minimum.  The ideal method was to have one single USB cable that could feed a 4-port USB hub inside the panel assembly.  The one obstacle to this theory was the Kidsball, which comes with a serial cable.  The serial connector wasn't going to fit thru the narrow wiring channel that runs to the back of the cabinet.  So I decided to try hacking the Kidsball so that it could interface with my Opti-PAC board...

OPTICS

The problem is, the Opti-PAC requires raw data directly from the optics of the device you're using, rather than the encoded data sent out thru the serial cable.  Kelsey at Oscar Controls was able to help me with the electronic connections, which are really pretty simple:

Optics schematic (courtesy Oscar Controls)

The above schematic shows how the optics from a cheap mouse can be used to send signals to the Opti-PAC, with the addition of a 220 ohm resistor.  Fortunately, I had an old generic mouse sitting around which gladly gave up its parts for the Kidsball.  I removed all the original components from the Kidsball circuit board, then replaced the original LED and phototransistor with the cheap mouse optics.  This is necessary because the original Kidsball optics don't send the correct signals required by the Opti-PAC.

The new optics installed

Following Kelsey's schematic, I used hook-up wires to jumper between the new components on the Kidsball PCB, and to make the connections from the PCB to the Opti-PAC.  Make sure you have the correct side of the LED facing toward the sensor side of the phototransistor (the emitter side of the LED usually has a small lens or blister).  Just make note of their positions before removing them from the mouse board and you should be OK.  And don't forget the resistors!  You need one for each set of optics (total 2).  This method will reportedly work with optics from common cheaper mice such as Belkin and Kensington brands.  

According to Kelsey, if you measure the voltage between signal (X1, X2) and GND, and it reads less than ~0.2V, then the current is "sinking" to ground. In this case, you must change the Opti-PAC polarity jumper to A/LO.  In my case, I did have to change the jumper to A/LO in order to work.

The Kidsball PCB with new optics and wiring

ENCODER WHEELS

The next obstacle in connecting the Kidsball to the Opti-PAC lies in the encoder wheels.  Since most cheap mice use encoders with larger "teeth", they most likely can not detect the very fine teeth on the Kidsball encoder wheels.  This causes the mouse pointer to exhibit erratic, jerky movement, or no movement at all.  The solution is to either replace the encoder wheel with another wheel of the same size but with fewer teeth (if you can find or make one), or to modify the encoder wheels so that the teeth are thicker, with wider spaces in between.  I chose to modify the Kidsball encoders.

X-acto brand hobby knife

First, you need to cut away every third tooth.  To cut the teeth, you need an x-acto knife.  The blade must be a new, sharp blade or you will mess up!

The encoder with every third tooth cut

Carefully cut every 3rd tooth as in this picture.  Cut by placing the tip of the blade near the end of a tooth (with the sharp edge against the tooth to be cut), and carefully inserting the blade further inbetween the teeth until it cuts the end off.  Do this slowly and carefully, don't rush or press too hard.  Now cut the other end of the same tooth.  Skip 2 teeth and cut again.  There will end up being 4 teeth together at the end, because of the odd number of teeth.  Carefully widen the gap between the 2 middle teeth so that light from the optics can shine through.  Do this by scraping away some of the plastic on the inside edges of the 2 middle teeth.  Careful!

The encoder with gaps filled

Now you can fill the holes in the leftover teeth with some fast drying 2-part epoxy filler, like JB Kwik Weld.  Use a flat toothpick to apply the filler between the close-together teeth.  Be careful to leave a gap when you get to the 4 teeth together, if some filler gets in there, just scrape it out with the toothpick.  If it's a little messy, you can scrape away the excess with the x-acto blade once it's all dry.  

Now pop the encoders back into the Kidsball frame and you should be ready to go!

The information on this site is for the purposes of education and entertainment only.  The owner of this site makes no warantees as to the accuracy of the information, and takes no responsibility for any damage or injury sustained due to the use of information herein.  The design of the Pac-Mamea cabinet and all photos, computer renderings, drawings, schematics, and printed information relating to such are Copyright © 2005 Robert Meyers.  No ownership of other copyrighted material found on this site is implied.