Using Midi to control standard Expression pedal parameters

[sidewinder]

Hello, is there any way to use  midi cc to control an effect with a standard TRS  resistance expression pedal input (ex: Roland EV-5) ? I assume it would take a type of converter to transform Midi CC to a resistance value. How can it be done?

Thank you!

[Seljer]

You can find plenty of kits an devices that do "MIDI to CV" (control voltage) for those people with the modular synths and such. Once you have a voltage with some simple circuitry you can make it control a resistance (optocouplers and such).

You could make such a device from the ground up too, you'd use a basic microcontroller to read and decode the MIDI signal and then generate a proportional voltage (most likely with PWM smoothed out to get an analog voltage).

[Processaurus]

Here's a midi to potentiometer kit:
http://highlyliquid.com/midi-decoders/mpa/

TRS expression pedals usually just take a voltage in on the ring, and use the pot as a voltage divider, and connect the wiper to the tip, so really all you need to fool the main pedal into thinking you have an expression pedal is a voltage between 0v and whatever it is putting out on the ring.  Some use 5v, lots of modern digital pedals will be using 3.3v, there are probably some that use something else.  If you went midi to CV, then you would need an attenuator switch to scale the CV down to the pedal.  With the midi to pot converter kit, you wouldn't need to have an intimate knowledge of the pedal you were using it with.

[sidewinder]

Thank you for your replies.


That kit from MPA looks interesting. I know the Diamond Memory Lane 2 needs an expression pedal with a minimum of 100K so I'm guessing I would need the 100k model. But I notice there are no output jacks on that device. If I get the kit, what further steps would I need to use it for the conversion?

Thank you!

[sidewinder]

Once the MPA kit is built, do I just have to solder a MIDI jack to the MIDI in terminal, 4 TRS jacks to the pot output terminals, a power in jack to the power terminal  and place it all in a nice enclusure?

I'm guessing you have to then connect it to a pc vi a MIDI to program the firmware using the utility on the site. How do I regulate the output voltage to 5v however? Doesn't an expression pedal just read the voltage (usually 5V on most pedals) and just feed it back to the pedal at a range between 0 and 5 to control the intensity of the parameter? So then does the MPA even give off an output voltage for my needs?

I'm also a bit confused betwen which pot value to get. A roland EV5 is only 10K and apparently it works with the diamond stuff. But in the Diamond memory lane manual they mention that you should use 100K minimum for the feedback expression pedal. Does this mean I should go with 100K ? What are the possible downsides of using a too high resistance value for the exp pedal as opposed to too low?

Thank you!

[sidewinder]

bump!