MIDI Merger
Two signals for one receiver
Published in issue 288, May 2000
 Whenever two MIDI signals have to be combined to drive a receiver, you need a MIDI merger. In the design presented here, two coupled microcontrollers merge the data.Since the MIDI signal is unidirectional and sequential, the data are transmitted without any feedback from the receiver. This means that it is not easy to simultaneously combine the signals from two MIDI sources. However, it can be desirable to combine the data streams from two input devices in order to drive a single destination device (such as an expander). This function is performed by a device called a ‘MIDI merger’. It produces a meaningful signal from the combination of several data streams from different sources. This is not a simple task, since the data can range in length from a single byte for a control instruction up to several hundred bytes for SysEx instructions, and the tone information can vary considerably (it is frequently sent as ‘running status’, occasionally interrupted by SysEx instructions).
Resistors:
R1-R4 = 220Ω
R5,R6 = 1kΩ8
Capacitors:
C1,C4-C8 = 100nF
C2 = 18pF
C3 = 22pF
C9,C10 = 100µF 25V radial
Semiconductors:
D1,D2 = 1N4148
D3 = 1N4001
IC1 = 74HCT14
IC2,IC3 = CNY17-2
IC4 = Atmel AT90S2313 (programmed, order code 996531-1a)
IC5 = Atmel AT90S2313 (programmed, order code 996531-1b)
IC6 = 78L05
Miscellaneous:
K1,K2,K3 = 5-way DIN sockets, pins arranged at 180°, PCB mount
K4 = mains adaptor socket
PCB, order code 000021-1
Disk (project source code file), order code 996038-1
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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