G, The bell board works off serial 9 bit data, not a DC offset. I doesn't work in conventional. The RCDR is there to provide the 9 bit data. If you used this in a legacy engine you wouldn't need the RCDR, only the Bell Board. the Bell board is basically a decoder that takes the bell signal and outputs a 7V DC level to energize the bell coil instead of an audio board. I am using the motor instead of a bell coil.
I used the RCDR because I wanted to try this on a TMCC engine. The original R2LC still provides the signal to the RS4 board and the RCDR to the Bell board. As long as you address the RCDR as a TMCC engine the bell movement and sound stay in sync. If you address the RCDR as a Legacy engine then the bell will sound after the movement stops
