Scratch Box Moves Forward!

I am currently revising my scratch box interface and thought I would post a few of the research and development photos as I turn a pivotal corner.

This is a voltage controller for an external processor.  A very simple circuit – 2 x 1k potentiometers.  I am currently in the 7th (?) generation of the scratch box, but this is the 2nd using my new processor.

The problem was creating the right ratio.  The main potentiometer swings 270 degrees. This got in  the way of scratching where I determined that a 90 degree swing (actually 2×45 degree bidirectionally) was idea.  So I needed to create a transmission with a 3:1 ratio from the touched interface to the potentiometer controlling the voltage (instructions) to the processor.

Here is an image from the “rubber band and duct tape” builds exploring the “ratio”.

How to accomplish the ration (transmission)?  Rubber bands WAS NOT the solution (the elasticity was not welcome). Belts proved a pain in the ass, then the solution hit me. Gears!

But where will I find cheap gears?

Remote control car parts – of course.  (showing my historic geek here – used to race these things…).  Specifically pinion and differential spur gears.  They come in 3 pitch (32, 48, and 64) relating to gear tooth specifications.  I am using 32 pitch in these next photos:

The potentiometer is suspended and allows the gear size to change as well as the z-axis as we know how multiple potentiometer shaft sizes are available.


This prototype is mounted on a 3/8″ ~6×6 of plexiglass.  The CD is on the otherside of the gears and this is where I interface with the controller as seen here.

This is the rough completed prototype.  Working well, tweaking the design and finishing design ideas as I lean into a production level prototype to put on the market as an “after product.  The good news – this is NOT a limited hardware application – this is a Roland EV5 expression pedal with a custom interface. You can use this CD controller with any expression pedal plug – so start thinking about how this can help you!