Everybody has his own idea about the CAB to HUMAN interface. Some want big knobs, pushbuttons, rotary encoders without stops, meters or digital readback et al. We have developed our preferances after trying just about everything imaginable, and have documented the Mainline Control System on the Teton Short Line, but we haven't mentioned the Yard cab at Malfunction Junction (MFJ) until now. With the advent of DCC, the old yard cab wouldn't do. It was an ancient MRC power pack, long ago converted to an SCR system for excellant low speed switching, It has a comfortable crank shaped handle so that you can feel as well as see the setting. We like it for yard switching, frequently leaving the speed set very low while just working the direction switch to separate magnetic couplers. It mechanically fits into the overall control system for MFJ.
When you got a good thing, why change it? Looking at it another way- If it's not broke, then don't fix it.
Ok, How do we make it run DCC. The rotary knob position must somehow tell the computer to generate the right DCC speed settings. This means we must generate a digital word (8bits) that equates to the shaft or knob position. We really need only 5 of those bits to resolve up to 32 positions and we run our decoders with 28 speeds. Even less than that because of the "Start Voltage" offset. Another 2 bits can be used for the direction switch and the emergency (panic) button. Got a bit leftover- Oh what to do with it?
To us electronic types, thoughts of stuffing the MRC case with a circuit card, Analog/Digital Converters (ADC/DAC) and electronic "glue" to tie it together, come to mind. But- You live in the sticks and the junk box doesn't yield a suitable ADC or DAC, now what? Wait a week and pay premium for small mail-orders? Back to the drawing board, think back to simpler times and recall the Gray code shaft encoders. We can build that from the junk box and have it running by the end of the day. We did it and thought you might be interested in a bit of old technology that still works very well. Like some "poor" railroads of the past. You just got to look around at the roundhouse rubble and find something that will do the job.