I use NCE AIU01 for block detection and mostly use BD20s from NCE. I wasn't able to get some recently and got a couple of Digitrax BD4N detection units.
The AIU01 outputs 5v on each input and expects detection to close the loop to -ve common. However, the BD4N from Digitrax expects a +v common and each of the outputs is -v. So the opposite.
Does anyone know if I can use a BD4N with the AUI01?