Doodah

Thanks Smash, Is this up to the task? Specifically the SFH618-2. Seems about as simple as you can get and if I'm not mistaken, draws virtually no current: www.isocom.com/datasheets/db92370.pdf Just finalizing the parts list. Expect an order any second ;D

The desk is a Soundcraft B800 which is an old broadcast desk. If you Google it, the first result should be the page on Soundcraft's website which has pdf manuals, tech specs etc. There are 3 identical PSU's which I thought I could tap in to for the 5V but it seems they only supply +48V and +/-17v. Dropping the voltage to the +5 which I have measured on the ext. mute pins must be done somewhere in the desk itself. This thing is not particularly easy to work on - even with all the channels removed, so I think I'm swinging towards using a separate power supply for the MIDIbox and the excellent suggestion of using optoisolators in place of the usual LED's. If I understand correctly, I will be keeping the resistors but perhaps a different value than 220R, depending on the opto used? Any suggestions for a good combination? Can't wait to get started on this!

Good news! The external mutes set a VCA state so it looks like it's byebye relays. Thanks for the heads up - this should save a lot of work. Smash, please excuse the daft question but when you mention bypass caps on the +5/Ground lines, I think you mean in the MIDIbox (not the +5v logic supply on the console)? If so, where would be the best place in the circuit to add them? I'm guessing before / in place of C5 on the Core schematic? Also what would be a realistic value for the smaller caps on each connector? Sorry - electronics not one of my strengths.

Thanks. That's enough info. for me to go ahead and get the parts together. Not too worried about the hardware side of things but the programming aspects are a little scary! I definitely intend to use the SmashTV DOUT boards but I'm under the impression that I'd still require the relays (46 to be exact). If anyone knows of another way of shorting these pins to ground then I'd be interested to hear.

Hi, First post - What an amazing website! I'm trying to find a solution for midi muting channels on my analog mixing console (36/8/2). Each channel has a pin which just needs shorting to ground to activate the mute so I'm pretty sure it's a fairly simple job for MIDIO128 controlling relays. I need to control 46 relays in all but don't require any digital inputs. Is it OK to build a MIDIO128 with no DIN boards and two DOUT boards? If so, should I be disabling the DINs somehow - either in the firmware or terminating somewhere on the CORE or both? Just want to get everything clear in my mind before ordering parts. Thanks.