The goal in the development of the TT MIDI module was to create a universal and flexible platform which could easily solve most switching problems in guitar and bass amplifiers. The unit can be controlled by conventional (foot)switches as well as MIDI commands.
To fulfill these requirements while keeping the hardware to a minimum, the TT MIDI module uses the AVR u-Controller ATMEGA16, which includes the controller software as well as the memory for the MIDI programs.lt.
As the documentation for this module is extensive, and because further development is always possible, the current schematics and layouts are available as PDF files for download.
The input group 1 with inputs I1-I4 is conceived for channel switching. These inputs are "filtered" with extra circuitry, so that when footwitches are used, which are typically connected to the module over long cables, no additional interference is generated and the signal is cleanly and clearly transmitted.
Group 2, with inputs I5-I8, is for control elements, which may be mounted directly on the front panel. These inputs are wired directly to the input of the microcontroller, without additional circuitry. Lead lenght up to .5m is not a problem.
The outputs feed a ULN2803 driver. This permits controlling heavier loads, such as relays, and can deliver up to 500 mA.
In the standard configuration of the TT MIDI Module, pins Z0-Z2 are laid out as follows:
The main PC board includes two power supplies. The "Main Power Supply" is required to power the complete circuit and generates a voltage of 5 VDC from 6.3-9 VAC. Since this voltage can also be used to supply 5V relays, make sure the input voltage is high enough so that, after rectification, the 5VDC is stable under load.
The microcontroller is forgiving as far as voltage is concerned, and works even by lower voltages, but low voltage can cause the relays to lose retention and can, through vibration, "flutter." Furthermore, depending on load, the 7805 may require an extra heat sink.
Caution: the 7805 can handle a maximum of 1.5A. Do not exceed this current load. Finally, we recommend that this circuit be protected with a dedicated fuse on the input.
The "Extra Power Supply" can be used to supply other voltages; for example, 12V for the operation of 12V relays, or 9V for providing phantom power to a MIDI device.
The extra power supply can also be used to step-down high AC input voltage; for example, to reduce 15V to 9V, and then feed it into the main power supply to produce 5V. The extra power supply has the same cooling requirements as the main supply.
The TT MIDI module does not have to be controlled by MIDI; it can be controlled with simple footswitches, or controls mounted on the front panel. (Footwitches on and front-panel switches must be momentary contact switches OFF-(ON)).
Pushbuttons are necessary to associate a particular configuration with a MIDI program. They are used to set the configuration, which is then assigned to a MIDI program number.
The TT MIDI Module works with "program change" commands and receives these on channel 1. Most of the switchers on the market work with this channel, especially the simpler switchers where no direct channel selection is possible, so everything should work together. If necessary, a microcontroller can be provided which can be programmed
on other channels.
The process to assign a configuration to a particular MIDI program is
Since software version 2.x it's also possible to process „controller changes“. Now it is possible to select individual channels regardless of the chosen program.
Furthermore it is possible to select the MIDI-channel via CC and to reset the memory of the controller back to the original state.
Definition of the CC:
#81 Channel 1 / Out 1: Value: > 64 = ON
#82 Channel 2 / Out 2: Value: > 64 = ON
#83 Channel 3 / Out 3: Value: > 64 = ON
#84 Channel 4 / Out 4 Value: > 64 = ON
#85 Switch 1 / Out 5: Value > 64 = ON, Value < 64 = OFF
#86 Switch 2 / Out 6: Value > 64 = ON, Value < 64 = OFF
#87 Switch 3 / Out 7: Value > 64 = ON, Value < 64 = OFF
#88 Switch 4 / Out 8: Value > 64 = ON, Value < 64 = OFF
#89 Switch 1 / Out 5: Toggle
#90 Switch 2 / Out 6: Toggle
#91 Switch 3 / Out 7: Toggle
#92 Switch 4 / Out 8: Toggle
#93 Mute Value > 64 = ON, Value < 64 = OFF
#94 Mute Toggle
# 102 Value > 64 Erase EPROM (Reinit)
# 103 Set Midi Channel Value: 1-16
# 104 Store Preset
# 105 Set Mute Time - NEW IN V2.1
# 106 Mute I5 -8 ON / OFF - NEW IN V2.1
To change the MIDI-channel to 2 the controller 103 needs to get addressed with the value 2 (for the 2nd channel).
A value >64 needs to get send to controller 85 to switch the output Out5 on.
If controller 89-92 receive a random value the current state gets reversed. So ON will result in OFF and OFF will result in ON.
The TT MIDI Module is supplied with an extra board for relays. This board does not include the components or relays. The components required for the desired switching must be ordered separately.
The TT MIDI Module can be used for completely different (switching) tasks. The main board includes a possibility to mount a 10-pin socket for a programming interface (programmer and software are not included).
To use the midi switcher as a looper a customized version of the program is available. With this software each output can be turned on or off and is independent of the status of the other outputs (actually only the outputs 1-4 are effected by this change). Nothing else was changed. The use and programming remains the same, also the muting function. Instead of foot pedals is recommended the use small momentary switched.
You can order the microcontroller which has this firmware installed in the online shop.
"Worst Case" note: depending on the relay used, the total current can exceed the current limit of the internal power supply ! Make sure to use low-power relays or a second power supply and a heatsink for the 7805.
#81 Switch 1 / Out 1: Value > 64 = ON, Value < 64 = OFF
#82 Switch 2 / Out 2: Value > 64 = ON, Value < 64 = OFF
#83 Switch 3 / Out 3: Value > 64 = ON, Value < 64 = OFF
#84 Switch 4 / Out 4: Value > 64 = ON, Value < 64 = OFF
#85 Switch 5 / Out 5: Value > 64 = ON, Value < 64 = OFF
#86 Switch 6 / Out 6: Value > 64 = ON, Value < 64 = OFF
#87 Switch 7 / Out 7: Value > 64 = ON, Value < 64 = OFF
#88 Switch 8 / Out 8: Value > 64 = ON, Value < 64 = OFF
#89 Switch 1 / Out 1: Toggle
#90 Switch 2 / Out 2: Toggle
#91 Switch 3 / Out 3: Toggle
#92 Switch 4 / Out 4: Toggle
#93 Switch 1 / Out 5: Toggle
#94 Switch 2 / Out 6: Toggle
#95 Switch 3 / Out 7: Toggle
#96 Switch 4 / Out 8: Toggle
#97 Mute Value > 64 = ON, Value < 64 = OFF
#98 Mute Toggle
# 102 Value > 64 Erase EPROM ( Reinit )
# 103 Set Midi Chanel Value: 1-16
# 104 Store Preset
# 105 Set Mute Time
The program MIDI-Send is a small tool for Windows to send either program changes or controller changes in a simple way. Raw data can also be transferred directly, if it is known how the bytes are constructed.
The program is available for free, use at your own risk.
No installation is required to use the program. Simply download the archive, unzip and run the EXE file. There must be a MIDI interface installed on the PC, which must be selected in the program.