I spent way too much time trying to puzzle out how to best control the 28V annunciators that I will use. I have a lead on how to make a 28V DC to DC converter, but I need a way to allow a lower voltage to be used for night operations. This is complicated by the fact that the signals that determine when the annunciators should be on are all HIGH = ON. I.e. I have four 12V signals that determines when to send power to the annunciators, but I will only have one 28V power supply. This would have been a lot simpler if the annunciators where controlled by grounding them.

I posted a question on the AeroElectric-List. No one answered on the list, but the guy who sold me the annunciators replied privately with a suggested schematic which will do exactly what I need.

Note - the annunciator labels in this schematic are not exactly the same as the ones I have. But my annunciators will be wired in the same way.

I went out yesterday and picked up the components I need. Now I have to figure out how to lay them out on the BusBoard prototype breadboard. I bought the BusBoard-3U-CONN, which has provisions for a DB-25 connector that will allow the board to be removable. I'm going to be on the road for several nights this week, so hopefully I will have enough time to puzzle out how to lay this thing out. I should be able to lay the components out in a small part of this board, then trim it down to a more manageable size.