Posted by: sebion | May 29, 2012

Encoders and a flat SMD board

Again It’s been a long time since the last update and a bunch of work has been done: I completely redesigned the physical modeling to a new acceleration based approach that takes the (of course adjustable) stiffness and frictional properties of the hammer jack connection into account. With this new model it have become quite convenient to play a note without having to fully depress the key.  Even the behavior of the catcher in an upright action has been modeled to make repetitions more realistic on those actions.

Finally I have decided to throw away the old 8 slider pot board and design a new user interface using 8 rotary encoders which will make it a lot more convenient to save, load and adjust keyboard settings. Here’s the prototype:


Another thing that had to be done was redesigning the sensor boards as the through hole version didn’t fit under the keys, cny70 sensors were a little bit expensive and crosstalk between adjacent keys has become an issue with the new physical model. Therefore I have designed an SMD version of my octoboard:


New features are:

  • Sensors (ITR8307 not actually smd but you can make them smd by bending and cutting the pins and they are very cheap) can now be equalized with smd pots in order to equalize the sensitivity and adapt it to a level where the highest possible resolution can be achieved with a particular keyboard setup
  •  Board can be as flat as <6 mm with smd design and atmegs avrs are a lot cheaper in TQFP44 package
  • This board is able to switch the IR leds in the sensors separately in order to minimize crosstalk issues
  • Simple 10 pin angled connector makes it easy to plug two boards together in order to form the sensor bar



  1. I don’t know about 6mm under the Hammond keys and I didn’t realize there would be a DIP package on the board also. I’ll have to get the tape measure out tonight. Is it possible to have just the sensors on the sensor bar and the balance of the electronics eslewhere or is crosstalk and remote wiring an issue? I would love to work with you on perfecting an installation for Hammonds, especially since I have one sitting in my garage and is crying for MIDI.

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