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Old 06-11-2015, 08:28 AM
Willo47 Willo47 is offline
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Join Date: Apr 2015
Posts: 2
Post Foot Switch For Roland GR55 Guitar Synth

MIDI Foot Pedal Controller for Roland GR55 Guitar Synthesiser

**** Photos and circuit diagrams have now been added which completes this post ******
**** Circuit diagrams have been upgraded to high resolution images 17th June 2015*****
I have put in this post as an example of how I used the Highly Liquid MIDI CPU to make a MIDI foot switch. I kept it simple to make sure that I could make this project without too many problems. I finished the project with virtually no problems other than some issues in finding the correct information which John (the mediator) did for me before I put in this post. I hope this may encourage others to give it a go. I am a retired electronics engineer and also have a good workshop to allow me to do the mechanical construction as well.

I am a guitarist/vocalist in a band and have just purchased a Roland GR55 guitar synthesiser to augment my pedal board system. The GR55 only has one foot switch which can be assigned for changes to the patches (the other 3 are for patch changes only which are too slow for in song use) and the inbuilt expression pedal was in the wrong place to be used in my pedal board. I needed a MIDI controller with 7 foot switches and one external expression pedal. Commercial pedal boards were either too large for me to fit into my pedal board and others available were much too expensive. Doing a search for MIDI control computers I came up with the Highly Liquid MIDI CPU as being able to do the job as well as being very reasonably priced. A pre sales query was answered immediately which was encouraging so I purchase a couple of MIDI CPUs (one spare).

The controller consists of 7 momentary foot switches with an indicator LEDs for each as well as a resistive expression pedal (external). I also have a TRS connector on the controller for one of the switches as sometimes it is useful to have a switch separate from the pedal box.

Additional to the MIDI controller the foot switch controller has a cable interface to a belt pack to which I can connect to in ear foldbacks (I cannot afford a wireless system). The interface in the foot switch also allows me to get the standard guitar pick ups and feed them direct to my guitar amplifier as the digitised guitar PU output on the GR 55 colours the sound too much. The belt pack also has a unity gain low noise buffer (identical to that used in the GK3 circuit) to allow me to plug in a standard guitar. Note a buffer is needed here to lower the impedance of the circuit otherwise there is too much cross talk with the multicore cable.

Note that all outputs and inputs are protected with resistors and diodes to the power supplies as shown.

The indicator LEDs were driven by the MIDI CPU via ULN2003 darlington pair drivers. I did this so that I could use the unregulated DC to drive the LEDs and also I didn't have to worry about using high intensity LEDs to limit current drain to keep within the MDI CPU power specs. As I only used one bank of 7 LEDs I did not need to use the multipexed select output of the MIDI CPU.

The following is the configuration code for the controller. I only used CC controll messages as patch switching (using program controls) is too slow in the GR 55 for live song use.

// Two layers are used in the configuration

F0 00 01 5D 04 01 // Sys Ex message header
00 // Layer zero
08 00 56 00 01 00 // Trigger high to low
09 00 56 00 02 00 // CC change toggle
0A 00 56 00 03 00 // sec 3.2.5 firmware V 1.2
0B 00 56 00 04 00 // for inputs 8 through 14 (0E h)
0C 00 56 00 05 00
0D 00 56 00 06 00
0E 00 56 00 07 00

00 00 2B 00 00 00 // LED data output
01 00 2B 00 00 00 // for outputs 0 through 6
02 00 2B 00 00 00
03 00 2B 00 00 00
04 00 2B 00 00 00
05 00 2B 00 00 00
06 00 2B 00 00 00

0F 00 2A 00 02 11 // Set output 15(0F h) to common output
// (not used in my circuit)
// Common cathode non inverting using register 11h
// as LED state register
17 00 0F 00 00 00 // Convert analog to 7 bit value and store in data
// register for i/p 17 h (0Ah)
17 00 04 00 08 0A // CC message generated for CC#8 data register 0A h

F7 // End SysEx message for layer 0

//Second layer config message

F0 00 01 5D 04 01 // Sys Ex message header
01 // Layer 1
08 00 76 00 11 10 // Toggle bit in data register 11 h (LED state register)
09 00 76 00 11 11 // for bits 0 to 6 corresponding to switch inputs 8 to
// 14 (0E h)
0A 00 76 00 11 12
0B 00 76 00 11 13
0C 00 76 00 11 14
0D 00 76 00 11 15
0E 00 76 00 11 16

F7 // End SysEx message for layer 1

1. A MIDI note on message seems to be created on the rising edge of each
switch trigger. I cannot explain this but it does not affect the GR55 as it
does nothing with note on messages.

2. When using the footswitch and using the guitar PU output I had to isolate the earth on the output to prevent an earth loop. I made a simple plug socket link with an earth break to find the earth loop then I replace this with a dedicated marked cable.

3. I bought a low cost resistive expression pedal which had a two 50k potentiometers which I paralleled up to make a single 25k potentiometer. With a cable lenght of 1.5 meters it works perfectly with that resistance direct into the MIDI CPU input without a buffer.

4. To connect the belt pack to the foot switch I used standard sub D 15 pin VGA connector which are cheap and readily available and used HDMI cable to wire it up as I needed two extra wires for the in ears.

5. Whenever soldering these small connectors make sure you plug them into the mating socket while soldering to give some heatsink and stop the heat misaligning the pins.

6 To make the shorter cables for the GK3 to belt pack and the foot switch to GR55 I bought a long Roland GK3 cable and cut it to lenths and bought some extra plugs to solder onto the cut ends.

Picture of the finished switch box and belt pack plugged into my pedal board

Picture of inside of foot switch.
Note I used headers on the MIDI CPU as I don't like soldering more than once on something as important as this. I used a small grinding wheel in my Dremmel to grind off the edges of the pins so that they would fit into the CPU card.


Picture of belt pack just before screwing in the VGA connector. Note you have to solder the connectors outside of the pack and fit later as otherwise you cannot access the connectors for soldering.


Circuit diagram of foot pedal system(excluding GK3 cable link)


Circuit diagram of GK3 cable link (part of the foot switch controller box)


Circuit diagram of belt pack


Last edited by Willo47; 06-17-2015 at 10:01 AM. Reason: Correcting minor changes after checking
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Old 06-12-2015, 02:44 PM
John's Avatar
John John is offline
Join Date: Jan 2009
Posts: 3,007

Willo47, awesome! Thanks for the project report. I look forward to seeing the pictures. Welcome to the forum.
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Old 06-15-2015, 08:23 PM
mapperboy mapperboy is offline
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Join Date: Jun 2015
Posts: 1
Default higher resolution schematic images?

Hello and thanks for the info about the footswitch, pics and circuit diagrams
I am a wacky, crazy, dedicated GR-55/VG-99 Guitar Synth owner/user!
I want to build the project, however the resolution of the schematic images when downloaded from the site is very poor; when I zoom in to read them they just become a pixel mess.
Can you upload some higher resolution images, please.
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Old 06-17-2015, 10:08 AM
Willo47 Willo47 is offline
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Join Date: Apr 2015
Posts: 2
Default Hi Res circuit diagrams added to GR55 foot switch project

Hi Mapper Boy, I have just figured out how to get some high res circuit diagrams onto my project post for the GR55 footswitch. Hope these are better.
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Old 06-22-2015, 11:38 PM
John's Avatar
John John is offline
Join Date: Jan 2009
Posts: 3,007

Originally Posted by Willo47 View Post
Hi Mapper Boy, I have just figured out how to get some high res circuit diagrams onto my project post for the GR55 footswitch. Hope these are better.
Great pictures and project!
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