After reading Rob's posting about the Hall Effect controller, I thought I give it a try. I did 2 other designs - FSR and Optical.. Both worked well. But the CAVEAT for the optical: sensitive top outside light. In my case light coming through the window cause the controller to be erratic. So this is another reason why I rather prefer a controller beneath the foot board.
With all the technology and website available to hobbyists now, I search around to accomplish 2 things:
1. create a schematic.
2. fabricate the circuit board.
I found 2 great websites for this:
1. KiCad kicad.org. Give you all the tools to create your schematic with a library of components to choose from; auto generated PCB from the schematic; easy routing to the components; a 3D Viewer of the final product; generate files needed for circuit board fabrication.
2. oshpark (oshpark.com. Easy submittal of generated files from KiCad. Under $7 US and free shipping for 3 circuit board

My Approach:
1. Purchased a Magnetic Field Sensor (T0-92 package) and Capacitor. The T0-92 is easier to plug into any hobbyist board and attach leads. TRS jack I have plenty. Prototyped the circuit with an external power supply. All good. Connected to the eDrumin module, using Expression Pedal type, All good.
2. Purchased same Magnetic Sensor but a SOT-23 package. Submitted the KiCad files to OSHPARK and purchased the 3 pack circuit boards for under $7.
3. Now the hard part ... the enclosure.

Final product:
I'll be going through the eDrumin calibration process when I can get to it.
The pdf link is here with pics from my google drive account:
https://drive.google.com/file/d/1_hAODf ... drive_link
go for it and have FUN