Hey all,
Just wanted to organize my thoughts and materials in some kind of public space where other people can weigh in if they so choose. I think I can maybe do this solo but if anyone has insights I certainly appreciate them.
I recently purchased a Boss RC-5 looper pedal for my midi controlled FX station. It boosts full midi integration.
After farting around for a couple hours unsuccessfully, I learned that the extensive midi implementation chart does NOT include any way to engage overdub mode through midi. Overdubbing can only be used by tapping the pedal itself, or by plugging in one of Boss’ remote aux switch thingies and assigning overdub to that control.
This absolutely massive oversight could be easily rectified with a couple lines of code and pushed into a firmware update. People are asking for it in forums all over the internet, so I have to assume boss intentionally hamstrung the unit to upsell the RC-10. From the bottom of my heart, screw you, Boss.
I plan on fixing this design “oversight” by making a very small midi device that lives in the battery compartment and shorts the remote aux switch pins to ground whenever a defined midi message is received.
My current plan is to see if the (now empty) 9v battery harness is receiving 9v from the power supply. If so, I can grab 9v off it, regulate it down to 5V with some kind of L7805 regulator, and power an ATTiny85 with it. The plan would then be to connect two of the ATTiny’s pins to some 2N3904 transistors as described in this thread:
The transistors are connected internally to the Aux input pins on the RC-5. I’ll probably need to drill a hole in the enclosure to get wires from the aux jack to the battery compartment.
With the the microcontroller powered, and able to programmatically pulse the aux switch inputs, we now need to get a Midi signal to the attiny85. I don’t believe Midi is well supported on the ATTiny85, but it is technically possible. Sources:
I could easily grab a midi signal from the RC-5’s built in midi through, and pipe it over to the ATTiny in the normal way, through an optical isolator. However, if possible I’d like to reduce the latency introduced by the Midi-through and instead grab a copy of the midi signal at the input. Based on my reading, it seems like it might be possible to passively split the midi input signal and have it drive BOTH optical isolators (on the RC-5 and the parasitic ATTiny device). It my also be possible for me to passively tap the signal AFTER the RC-5’s optical isolator and go straight to the ATTiny, bypassing any optical isolator on the Tiny. I’m still not positive exactly how I want to go about this, and I’ll need to experiment.
Anyway, if anyone actually made it through that trainwreck and has any thoughts, feel free to spam them at me. No obligations though, just wanted to organize my thoughts.
I also like that this device could essentially function as a midi controllable tap tempo mod for pedals that have tap tempo inputs like the JHZ Unicorn V2 to name a random example. Perhaps one could even integrate the Tiny straight into a cable and run it off the 5v signal found in the midi reference voltage, as Mitxela does here: MIDI on the ATtiny - mitxela.com
I considered using that approach, but I am a little worried it would cause noise issues. I have no idea if running the Tiny off the same 9v supply as the RC-5 will introduce noise. I guess time will tell.
EDIT: Bashed this together real quick to get my bearings. Haven’t built and tested yet but I think this might do the trick:
MORE EDIT: That draft layout was very wrong, replacing it with a new one:
