My synth requires control signals -5 to 5V for its VCA and VCF. Unfortunately the bela, bought specifically to provide complicated envelops, provides 0-5V at the analog outputs, and so falls short short of this. Here, provided for the good of Bela-kind, is a circuit you can easily make at home which translates 0-5V to -5 to 5V. The circuit has trimpots which allow you to calibrate an output of 0.5 from bela (ie 2.5V at the output of pepper) to translate exactly to 0V. This may be a bit fussy for your application, so you can leave the trimpots out if you like! The whole lot mounts to the back of the BBB via a transition plate and some polycarbonate nuts and bolts.
As you can see, I have substituted the 3.5mm sockets for banana socket to be compatible with the rest of my system and kept the 3.5mm sockets for the analog inputs to retain the pot functionality. For these inputs I have a couple of 'frankencables'.
The circuit solves the problem of interfacing the pepper's outputs and I'm now looking forward to using the extraordinary capability the bela offers. I hope this is useful to someone else!
