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PC case mod: MIDI sockets (like good old Atari)

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Hi MIDI & PIC hackers, I found midibox a few days ago and it gives me nightmares because I don't have time to start such exciting projects now. I like the ability to use COM ports as inputs for controllers. Now, before dreaming again, here is my first MIDI hack:

a PC case (Antec P160, all-aluminum, blue LEDs on frontal fan intake) has just been modded with two MIDI sockets on an unused 5.25 front bay. I thought that buying an external MIDI cable sux, the extra joystick plug is a waste (me never gaming, a joystick would only be useful around a MIDIBox core), and small breakout boxes hanging around a nice tower case sux too.

As expected, the motherboard UART MIDI OUT pin has not enough fan-out to drive an optocoupler's internal LED (hardware synth MIDI IN for example),then I added some TTL gates for buffering (NAND wired as two inverters).

The MIDI IN uses a 4N35 optocoupler and 1K pullup resistor without additional buffering. I did not check the waveforums with oscilloscope nor test long SysEx dumps, but playing a bit on a MIDI keyboard did not seem to show missing Note On/Off messages in MIDI-Ox monitor.

Here are the schematic, PCB in Eagle format. I added a 7400 NAND SMD package instead of my prototype with a DIL package hanging below the PCB with bare wire. The PCB has been optimized for homemade photo etching: larger traces, pads, vias, smaller drill holes. Happy case modding ! :o



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As expected, the motherboard UART MIDI OUT pin has not enough fan-out to drive an optocoupler's internal LED

Man, where were you when I needed you!!! ;D


I remember having to pull parts out to get that to work, but it went on forever. That machine is actually here at home now, and I'm currently using that interface. I've got mine routed to a 9pin D-sub socket on a PCI slot cover, but that requires a 9pin to dual MIDI cable.

Welcome aboard!


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A thought about safety, for hackers who don't power off before opening case, how is protected the +5V line on Asus MB's MIDI connectors ? Unless the front 5.25" bay interface is enclosed in a plastic case, there is always a risk that a soldered pin could touch the ground from chassis or a CD/DVD drive below. If someone has a spare motherboard, thanks for looking whether it's a fuse or a resistor and locating it, probably in SMD package.

Another suggestion, for recycling old ISA MIDI interfaces like the WinMan 2x2, useless on PCI(-express)-only motherboards: some MIDIBox-based controllers for a VSTI softsynth and VST host that can boot w98 & run from CompactFlash without display, on a PC-104 system with ISA connector, all in the same case as the MIDIBox... I don't know yet which softsynth to choose (probably not a CPU-eating monster). Any ideas ?

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