This information is for the relay-based MIDI switcher shown below. If you have the transistor-based switcher, use this information instead.


The relay-based MIDI-Switcher is an electronic device which uses incoming MIDI note information to activate its eight output ports.

These ports are switched between ground (on) and high impedence (off) and are designed to operate the inputs of a “standard” eight relay module.

The relay outputs can be used to activate solenoids, motors, light bulbs etc. For example solenoids could be used as robotic percussion instruments that could be driven from a MIDI sequencer or DAW program.

This manual assumes you have a the relay module attached to the Relay-Switcher board, and references to the output connections refer to the relay outputs.


Each of the relays works as a two way (SPDT) electric switch. The relay operates by mechanically operating the switch terminals.

Each relay has three output terminals, the centre terminal is the “Common” connection and it is either connected electrically to the terminal on the left or the right of it.

Because relays use mechanical switches, they:


The Relay-Switcher must operate with a 5 Volts DC Power Supply. If you use a higher voltage, the relay driver board may be damaged.

The power supply is connected to the terminal block beside the MIDI connection. Make sure you connect the supply with the correct polarity. Refer to the labels on the PCB.

The supply must be able to provide enough current to operate the relay coils. For this eight-channel relay module, the supply should be able to provide 500mA or more at 5VDC.


Relay-Switcher has a single MIDI-IN connection utilising MIDI standard 5-Pin DIN socket. Most MIDI equipment has such a connection, but with a computer you may require a MIDI interface with the appropriate connector. A cheap and effective solution is a USB to MIDI cable which connects to a computer USB port and provides standard MIDI input and output cables terminated in 5-Pin DIN plugs.

Remember each MIDI cable works in one direction only… Relay-Switcher requires a MIDI input only, so you connect it to the MIDI OUT of your controlling device. There is no communication back from Relay-Switcher to the controller. Keep this in mind when you are reconfiguring the device. Keep a backup of your customised configurations (as described later). You can’t download them again!


Once you are powered up, try sending some MIDI… the default settings programmed in the Microcontroller are as follows

PORT AC3 (60)PORT EE3 (64)
PORT BC#3 (61)PORT FF3 (65)
PORT CD3 (62)PORT GF#3 (66)
PORT DD#3 (63)PORT HG3 (67)

The default receive channel is MIDI Channel 1 for all ports and 20 milliseconds duration. Modulation of duty and duration is disabled by default.


The switcher is highly customisable. Please see this guide for information on how to change the settings in your MIDI switcher


The relays on the board are mains-rated and the ability to switch mains may be a factor in choosing this board.

However there are DEADLY risks associated with mains and any work you do with mains must be at your own risk. I strongly advise against using this module to switch main electricity unless you are qualified, experienced and competent to work with mains wiring

Always make sure you have an easily accessible method to isolate the mains supply in an emergency.

Supply Isolation

Read this section if you want to switch high voltage mains with this device

If you intend to switch hazardous voltages (e.g. mains electricity) it is important to understand the level of electrical isolation between the load you are switching, and the MIDI hardware (e.g. sequencer or laptop) sending the MIDI data.

You may be comfortable with this level of isolation. However there is an additional level of isolation available by separating the 5VDC power supplies used for the Relay-Switcher board and the relay drivers.

Usually the relay coils share a common 5VDC power supply with the Relay Switcher board itself. The circuits are joined in two places

This single supply mode is fine if non-hazardous voltages are being switched, since the primary isolation is the relays themselves.

However if you wish to take advantage of this extra level of isolation, you will need to