This MIDI Merger / Splitter is the special 2 input 5 output thru box which I designed from scratch while not being happy with other options.

It has two MIDI input ports which are merged together by a microcontroller and then split to five MIDI outputs. Programmed microcontroller is included with a PCB or Kit purchase.

It has optimized schematics for 5V and 3.3V MIDI sender devices, optimized circuitry for optocoupler to minimize false triggering and improve sensitivity. Finally it uses hex inverter with a Schmitt trigger for driving a stronger output signal. This makes it very reliable device. This is an active circuit, so it does require an external power. That’s the way it should be according to the MIDI specs.

There are two options for external power:

• To be used with a standard wall adapter 6-12V and 5.5mm*2.1mm connector. In this case a Kit comes with corresponding socket and 7805 power regulator

• To be powered from USB port. In this case a Kit includes USB->5.5mm*2.5mm cable, corresponding power socket (so you wont plug wall adapter) and doesn't include 7805. Instead of that you'll solder a jumper Pin 1 and Pin 3. Leave Pin 2 not connected. Please make sure, you use USB port or adapter with 5V output and verify it prior to connecting to the board. There are some QuickCharge USB chargers which can bump a voltage. Please, avoid using them.

Board size and an enclosure choice: Size: 5x17cm

Some of you wondered ideas for enclosure selection. Well, some kits produced here can be installed into cast cases, such as MidiThru-4 or MidiMerge_2in->5out into 1032L enclosure. It requires drilling and some patience. Other boards are just too big to go into typical aluminum case. I found it much easier to put them in between two acrylic panels cut to the size and connect them with plastic standoffs. I typically use M3 standoff 20mm and 5mm. 20mm goes on top, and has enough room to cover DIN5 sockets, while 5mm goes on the bottom. There is CorelDraw file on Github with precise board dimension and holes location.