Some forum dwellers do some midi DIY; this is a recent project.
I’ve been attempting to move a more into keyboards in addition to guitar so I got a used M-Audio Hammer 88 controller. This weighted controller has a pitch wheel, mod wheel, volume slider, sustain pedal, soft pedal, and an expression pedal. I like to have a keyboard at home and a keyboard at practice (only carrying a USB stick to practice is very easy on the back…), so I decided to modify my daughter’s Casio CDP-100 weighted 88 key that is collecting dust. It’s got speakers, reverse polarity sustain pedal, and a 5-Pin DIN midi out, but nothing else. It “feels good.”
There are some quirks about the CDP-100 that I wanted to correct AND add functionality:
- Add midi controllers to match the Hammer 88 (make a much cheaper duplicate with the CDP-100 weighted keys)
- Fix the blasted 5.5mm x 1.5mm reverse polarity DC connector
- Add a way to merge a future keyboard into the midi IO stream
- Add a way to merge an Art-11 midi foot pedal (and 12VDC power) for program changes
- Merge the CDP-100 midi output with all new controllers and signals.
- Use a normally closed sustain pedal (like Yamaha FC4)
- Add some LEDs to confirm location of new controllers and Midi IO
I took pictures of the construction sequence. It’s a wooden enclosure that replaces the left side of the CDP-100 and contains an Arduino Mega, all the controllers, the Midi IO, etc. Pictures are pretty self explanatory.
Notes:
- Midi requires Opto Isolators on input, so an Arduino shield was made to house the simple electronics. There are three midi inputs and one merged midi output to Cantabile.
- Pitch and Mod wheels are not full travel! Even though the pot can move 300 degrees, the wheel only moves 90 degrees. That’s a lot of resolution loss and midi pitch is 2^14 resolution. An Arduino analog input only has 2^10 resolution from 0-5VDC, so the smaller pot movement degrades the pitch resolution more. I ended up using an Exponential Moving Average for the Pitch wheel to try to provide “fake” resolution. Every loop sends an updated pitch CC until it reaches the pot position.
- Other than removing the left keyboard cover, there were no modifications to the CDP-100. It can be returned to normal with two bolts.
- The enclosure seemed roomy until the wires were added!
- Pots are noisy! So every analog controller input as a deadband to avoid flooding the midi IO. Also, every output has an if-then to never send a duplicate midi CC value.
- Use resettable fuses (the four tan components in a row) on all 5V outs to pots/pedals/switches, especially those with TRS jacks. I’ve blown Arduino internal 5V voltage regulators when inserting 1/4 TRS plugs because there can be a momentary shunt from 5V to Ground.
I’ll probably add few more comments when I review.
