MIDI Relay Units

 The 4 and 8 MIDI Relay units can be used in conjunction with the MIDI to 24 Outputs unit 

The MIDI relay units consists of:

• 8-way screw terminal connections for inputs and outputs, 
• a Light Emitting Diode (LED) associated with each input, 
• 2-way Power Supply screw terminals  and associated power-on LED,
• 2-way screw terminals for a  Common Volts Loop,
• Open Collector Transistor drivers for each relay and associated back E.M.F. diodes in parallel with each relay.

The MIDI relay units require:

• a Power Supply voltage,
• Connecting to the MIDI to 24 Outputs unit.

Operation:

The inputs of the relay units are fed directly from the MIDI to 24 Outputs unit outputs. Each relay is switched ON when a positive voltage (+5 Volt) is applied to the input. There is also a Light Emitting Diode (LED) associated with each input and each board has a power-on LED. The corresponding RELAY STATUS LED lights while the relay is closed. 

One side of each of the Normally Open (N.O.) Relay switches  is connected via a wire Link to a Common Volts Loop, this allows a single Common Voltage to be connected each of the relay switch outputs. However if a different voltage is required to be switched by different relays then the relevant wire Links can be cut and the voltage wired directly to the relevant screw terminal. Also the Common Volts Loop screw terminals can be looped from one board to another to allow expansion.

Purpose:

The MIDI relay units can be operated live, in conjunction with the MIDI to 24 Outputs unit,  in real time from a MIDI keyboard or from a hardware/software sequencer with pre-programmed MIDI Note on/off data. The relays can be used to switch electrical devices, such as lights, motors, pumps etc., in time with the music. Use the relays to control  tape decks, or energize and synchronize auxiliary circuitry. This provides a direct interface to the world of analogue electronics. 

Specification: 

The relays are rated for: 

• Switching capacity: 10A @ 125Vac, 6A @ 277Vac, 10A @ 16Vdc 
• Operate/Release time: 10mS/10mS 
• Coil Impedance: 69.4 ohms
• Coil Consumption: 360mW
• Contact Material: Silver alloy

MIDI Specification: 

Relays 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, all relays will switch off if the 'All Notes-Off' command is received. This MIDI command is  channel independent.

Expansion:

The MIDI relay units can be combined and expanded so that a single MIDI input can be fed to multiple MIDI relay units.

TOM SCARFF
1 Martello Court
Portmarnock
Dublin
Ireland.

Email: tscarff@eircom.net