stan2004 posted:More info is needed on how the DIN input works; it stands to reason this configuration was considered when the Atlas signal system was designed.
If no one comes forward with the "secret" to DIN operation,
Hi Stan,
I traced out all the various boards on my Custom Signal/Atlas signal installation (schematics available upon request, no guarantee they are perfectly correct ). Basically DIN (and most other inputs) are pulled high by a 47K resistor to +5V. This high runs through a series 470K resistor into the PIC 16xxx processor.