I'm not a particulary versatile guitar player and my needs on stage are quite simple. All I need is a small foot controller with some buttons and one expression pedal. The foot controller should be small enough that I can store it on my 6U rack when I'm done. If I can power it and communicate with it using only one cable even better.
After I purchased a Kemper Profiler I looked all over the Internet for an affordable foot controller that would meet my requirements. In this search I found the Line 6 FBV Express™ MkII, which has all that I need but has the caveat that it cannot be connected directly to the Kemper Profiler as it uses a proprietary communication protocol and full-duplex RS485 instead of MIDI.
In the following sections I present a reasonably inexpensive solution to create a hardware/software converter to allow the foot controller to interface with the Kemper Profiler. Most of the hardware I used was lying around gathering dust and this project seem to be a good one to use them and learn a few things in the process.
- SparkFun RJ45 Breakout
- SparkFun RJ45 8-Pin Connector
- Olimex MOD-RS485-ISO
- Olimex SHIELD-MIDI
- Olimex STM32-E407
- Olimex ARM-USB-TINY-H
The FBV Express™ MkII uses a RJ45 connector for communication and power. The communication interface is full-duplex RS485 and the device can be powered from +8VDC to +9VDC, in my hardware project I chose to use +9VDC as +9VDC power supplies are easy to come by. The signals on the RJ45 connector can be easily accessed using SparkFun's RJ45 Breakout and 8-Pin Connector. However, you should keep in mind that the square pin of the SparkFun RJ45 8-Pin Connector is pin number 8 and not 1. The correct pin numbering of the SparkFun RJ45 8-Pin Connector is given in the following image:
The pinout of the RJ45 connector from the host side is as follows:
| Pin Number | Function |
|---|---|
| 1 | RS485 TX+ |
| 2 | +9VDC |
| 3 | RS485 RX+ |
| 4 | GND |
| 5 | +9VDC |
| 6 | GND |
| 7 | RS485 RX- |
| 8 | RS485 TX- |
In order to use one MCU 3.3V UART to communicate with the floor controller we need an RS485 converter. The following table shows the correct connection:
| SparkFun RJ45 8-Pin Connector | Olimex MOD-RS485-MIDI |
|---|---|
| 1 | Y |
| 3 | A |
| 7 | B |
| 8 | Z |