This video demos a DIY light theremin controller for synths with expression pedal inputs.

via ChrisLody:

I was looking for information about the pinouts for expression pedals because i realised that my pedal that works on my yamaha won’t work on my ks5 and found this page:

http://www.soundonsound.com/forum/showflat.php?Cat=&Number=322584&page=0&view=collapsed&sb=5&o=&fpart=1

This basically explains that expression pedals are just a simple voltage divider which i realized can easily be built from a couple of light dependent resistors. So i knocked this together in about 5 minutes from an old headphone jack and a couple of ldr’s and it works a treat!

The connections may be different between manufactures but it works well on the ks5. With an equal amount of light hitting both sensors it rests in the middle position. The as you move your hand to cover each sensor the output is moved in either direction.

The ks5 allows the expression pedal to be assigned to any midi cc so here its controlling the filter cutoff. This can be sent through midi into your DAW to control anything you want. Nice.

I will definitely be building a more permanent version of this! I’m also pretty sure this design could be adapted to make a diy breath controller that can be plugged into the expression socket so i’ll have to try that too.

if you want to try building one yourself its similar to the diagram in the link below. Just replace the resistors with ldr’s and the 3 outputs go to the ring, tip and sleeve of your connector. Experiment with different configurations until you find the right one for your keyboard:

http://www.facstaff.bucknell.edu/mastascu/eLessonsHtml/Resist/Resist3A12.gif