On Thursday I was able to get in to the electronics labs and test the connections of the Kaoss Pad. I used an oscilloscope to test the voltages of each of the six connections under a variety of conditions.
These conditions were:
Hold button OFF without using the touch pad
Hold button ON, X and Y on pad set to 1,1
Hold button ON, X and Y on pad set to 9,1
Hold button ON, X and Y on pad set to 1,9
Hold button ON, X and Y on pad set to 9,9
Hold button ON, X and Y on pad set to 5,5
Hold button held down
When touching the touch pad with hold button ON and OFF
Through this I learned that, as expected, a constant signal runs on every connection at all times. This is 6V peak-to-peak on all but one of the channels with a time period of 20ms. When the hold button is pressed down, the voltage is raised to 8V which causes the hold function to switch between the on and off states.
Standard waveform when XY pad is not touched.
All of the recorded values shown below were taken at
the guitar end of the connection, though these were checked and found to
be the same as at the Kaoss pad end and so only one set was written down. This suggests that the serial cable has no noticeable effect on the signal.
Results page 1
Results page 2
It was also shown that when the touch pad is used, regularly spaced spikes appear in the waveform. They are approximately 0.2ms wide in total and about 2V high. Their shape is changed depending on the position of the finger on the pad. This variation controls the stored parameters of the KP unit.
I have just completed a user testing session with 7 participants. Each was given five to ten minutes to play the guitar and then asked to complete a short questionnaire about their usual playing habits and their thoughts about different aspects of the guitar.
I will be using this information as well as that of any additional participants in the evaluation of the finished guitar.
The questionnaire that was completed can be found here.
The studio has been booked for an hour on Thursday the 15th of March for User Testing. If further feedback is required then I will book a second session as soon as possible.
I also hope to access the electronics labs over the coming week to test the connections to the kaoss pad.
After a brief meeting with my project supervisor yesterday, I am now ready to move on to the testing phase of the work.
Although there are still some corrections, changes and
adjustments to be made to the guitar, I plan to leave them until after
the project is complete since it is currently in a usable state and I
don't want to risk breaking anything before it has been tested!
Over the coming weeks I will use the university electronics labs to thoroughly test what has been built. I will also book one of the studios and revisit my planned questions for user testing.
Today I finished the build section of the project! I began by cutting a part of the same plastic box used for the front kaoss pad mount to fill the gap in the kaoss pad body where the touch screen was. I then attached the serial connector to it. This is not ideal as a permanent solution as it renders the LEDs inside the unit useless and so I may replace this with clear perspex or something similar at a later date.
I then used more of the same plastic to make a scratch-plate to replace the yellow one provided with the guitar and cover for the back of the guitar. It's not the most elegant solution but will do for now!
Finally I glued the nut to the headstock of the guitar and screwed on the truss rod cover.
I was then able to put strings on the guitar and plug it in to an amp!
Completed guitar & kaoss pad
The guitar circuit works, though the tone pots do not work properly so this will need re-soldering, however for the time being the guitar and kaoss pad are both functioning.
So, the only remaining problems to deal with are:
Setting the intonation of the guitar
Fixing the tone pots so that they work correctly
Finding the source of a slight hum that is only really present when the kaoss pad is turned on (possibly an issue with the lack of shielding between the guitar and touch pad wiring inside the guitar)
Then the purely aesthetic changes I would like to make include:
Replacing the black plastic with something more durable, particularly the replacement screen on the kaoss pad body.
Replacing the yellow hardware
Add the originally planned LED circuit behind the touch pad
I plan to upload a demonstration video of the completed guitar once the intonation is properly set up to make the guitar playable.
Today I have begun my final push to finish the build portion of the project and, after a very long day, am nearing completion.
I began by spraying a few extra coats of paint on to the body. While waiting for these to dry I soldered the wires on to the four touch pad connections to allow these to be connected to the serial connector in the guitar.
Touch pad connections soldered to wires ready to be put in to the guitar
I also cut a front mount to hold the touch pad in place on the guitar body. This was cut from a plastic box but may be replaced at a later date if a stronger and/or more attractive material is found.
The front mount cut for the touch pad
Once the paint was dry, a chisel was used to carefully level off the top ridge of the support for the touch pad and two additional pieces of wood were screwed in to either side of the kaoss pad cavity to brace the touch pad against the front mount.
Touch pad cavity with supports on three sides and a small section filed out at the bottom to allow space for the ribbon cable to fold own in to the hole.
Some parts of the outside edge of the guitar body would not allow the paint to stick and so have been left for now so that the electronic side of the project can be completed. I will most likely come back to these after the project is finished.
Part of the body where the paint would not stick.
Next the various parts of the guitar electronics were added to the body. The bridge and tailpiece bushings were hammered in to place as the holes drilled were a very tight fit. Then the pickups, selector switch and volume and tone potentiometers were put in to place with wires fed through to the various cavities.
Pick-ups and 3-way selector in position with wires fed through the cavities to be connected
The Pickups were then soldered to the pots. The main problem at this stage was that the wiring provided had already had some of the soldering completed but what had already been done did not match any wiring diagrams that I could find, however I managed to combine information from several to complete the circuit.
Volume & Tone Pots in position and wired up
Then the three-way selector was wired up. This was difficult due to the fairly low quality of the wires that came with the guitar body.
3-Way Selector Switch connected up
While the volume and tone pots were being connected up, the hold button was also put in to place and the wires connected to it fed through the additional hole drilled for the kaoss pad wiring.
Hold Button in position between the volume & tone pots
The pickups and pots were then all connected up the the input jack which was screwed in to place.
Input Jack Connections: 1 = Hot, 2 = Ground, 3 = Input Jack Tip
The two wires for the hold switch were then connected to the serial port. Once all of this was complete the touch pad was put in to the guitar and wired through to this same serial port.
Hold Button connected to serial connector
To ensure that the various kaoss pad connections matched to their original locations, the serial port on the guitar was wired identically to the one on the kaoss pad using the arrangement shown here:
1-4 = Four Touch Pad Connections, 5-6 = Hold Button, X = Unused
Finally, the tuning pegs were attached to the headstock of the guitar and the kaoss pad connection was tested.
Tuning Pegs attached to head
The remaining steps should be completed tomorrow. These are as follows:
Cover the back of the kaoss pad cavity
Glue nut to the headstock
Add scratch plate to the guitar
Put strings on the guitar and test the pickups/pots/selector switch
Attach strap buttons
Cover the hole in the kaoss pad & attach the serial connector to the cover.
