While quiet, I have been busy.
First, I have a second run of the Duophonic keyboard PCBs in and will stuff one this weekend hopefully. I have a couple of solutions to turn a MIDI keyboard into a pseudo "buss" type keybed so it can drive the duophonic electronics. Despite all the MIDI 2 CV converters out there, none create CVs, gates, and triggers the same way the Steiner Duophonic electronics did. So here the gist of the conversion process.
1. Use a Doepfer MTC64 which basically converts a MIDI "Note On" message to a TTL voltage. There are 64 outputs so you get 64 individual 5 volt gates which can drive an external device.
2. Use the TTL level signal to turn on either a solid state relay or a reed relay which acts as the buss switch. Build a series of 61 of these relays to emulate a 61 key keybed with a voltage divider connecting the switches.
I've fiddled around with this and the reed relays seem to offer the most promise, but it's expensive at a couple of dollars per relay. The solid state relays are more compact and have a great turn on time, but there is a decay on the turn off time as well as higher effective contact resistance. So, I think the reed relays are what I will use.
Next, I have the first Microcon prototype PCBs in. I just need to build one and test it.
I would also recommend this blog:
He's done a great job and has some great comments and advice. Thanks!