Build your own MIDI projects
Frequently Asked Questions.
MIDI & Music
MIDI and Music Information
MIDI to 4 Outputs




This unit utilizes MIDI Note ON/OFF data to switch 4 Relays which can be used to control Red(R), Green(G) and Blue(B) LED string light arrays. Note that this unit is designed to work with LED string lighting arrays used with Drumlite, but can be used with any common Anode LED strings.


This unit can work in standard MIDI mode or via the USB connection. It defaults to standard MIDI Baud rate of 31250. By replacing the original firmware on Mega8u2/16U2, the Arduino Uno will act as USB-MIDI device (Standard Midi Class), you don’t need to install additional device drivers on Windows, MaxOSX, and Linux, as the firmware acts as a device of Standard Midi Class. It will automatically install on the system as an Audio USB Device.




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MIDI Notes to 4 Relays Out


PRICE:  €70.00












The MIDI to 4 Outputs unit utilizes:

  • An Arduino including a suitable pre-programmed Atmega microcontroller,
  • A 2.1mm power socket, and associated LED, 
  • A 4-way DIP switch, which selects the MIDI channel, shown in table 2
  • A 150mm wired MIDI 5-pin DIN input socket,
  • A 150mm wired MIDI 5-pin DIN output socket,
  • Output Note selection is preset in the firmware to MIDI Note Numbers 36, 37, 38 and 39, 
  • A 4-Way Relay board.



The MIDI to 4 outputs also requires:

  • A suitable 12 Volt DC power source


Circuit Schematic and Boards:










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The MIDI IN and OUT connectors use  5-Pin 180 degree DIN sockets. Note that the MIDI IN/OUT wiring is polarised and the correct pins should be used.





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Output Current Drive:

You can get a maximum of 40 mA (milliamps) current from each output of the ATmega microcontroller board separately. But the maximum combined rating when several pins are active at the same time  is 200 mA for all pins.


Since the LEDs total current can be about 4A (4000 mA) the relay interface board is required. The relays can switch up to 10A at 12 Volt DC.


However it is probably best not to run the outputs at their maximum rating.


Normal Mode:

The unit detects the incoming MIDI data and if the MIDI channel corresponds to the correct MIDI channel setting, when a corresponding Note-on is detected, (to the pre-set note-on  data), the corresponding output is switched on (0 Volts) and stays on until the corresponding note-off is detected and the output is switched off (+5 Volts). This allows each output to operate independently. 


Relay Selections:





1 C2 36
2 C#2 37
D2  38
4 D#2 39

MIDI Note Numbers





The MIDI to 4 outputs unit can be operated live in real time from a MIDI keyboard or from a hardware/software sequencer with pre-programmed MIDI Note on/off data. The outputs can be used to switch electrical devices, such as lights, motors, pumps etc., in time with the music. Use the outputs to control and synchronize auxiliary circuitry.



MIDI Specification: 

The outputs are switched ON via MIDI 'Note-On' commands and OFF by MIDI 'Note-off' commands. These MIDI commands are all channel (1-16) dependent. Also, the outputs will switch off if  a correct MIDI Note On with a velocity of 00  is received. The unit also works in MIDI Running Status mode.





DIP Switch Selections



4 3 2 1
on on on on 1
on on on off 2
on  on  off on 3
on on off off 4
on off on on 5
on off on off 6
on off off on 7
on off off off 8
off on on on 9
off on on off 10
off on  off on 11
off on off off 12
off off on on 13
off off on off 14
off off off on 15
off off off off 16

Table 2 MIDI Channels



Power Supply:

An external 12 Volt DC power supply can be used to power the external LED string light arrays and also the Arduino if it is not using/powered by the USB connector.


The  Arduino can be powered via the USB connection or with an external power supply. The power source is selected automatically.


External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack.


Or else connection from the 12 volt power supply can be inserted in the Gnd and Vin pin headers of the POWER connector. A low dropout regulator provides improved energy efficiency.




Drumlite 5 Pin XLR Wiring:




Pin 1 - black cable (+12 Volt)
Pin 2 - red cable 
Pin 3 - green cable 
Pin 4 - blue cable 
Pin 5 - none




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