With some TMCC upgrades, or even adding the Cruise Commander M to some locomotives, the serial data stream from the R2LC (or R4LC) gets overloaded and doesn't properly trigger either the motor control or the sound. I previously created a transistor buffer to correct this, but that doesn't always work. I set about finding out why it would sometimes fail, turns out it's the amplitude of the serial data, not the actual drive impedance. Since the transistor buffer was an emitter follower, it didn't increase the amplitude, which turns out to be the bigger issue. So, back to the drawing board.
I came up with this. It's a 2x amplifier using an op-amp that also provides at least 20ma of drive if needed.
Simple circuit, any caveman could do it.
It accomplishes the goal, with a 2.5v P-P input signal, it outputs a rail-to-rail 5v P-P replica. Even adding a 470 ohm resistor load didn't phase it, the amplitude remains almost exactly the same. The 5VDC required can be stolen from the R2LC 5V lines on that board's pin-19 & pin-20.
The actual board is pretty tiny, .3" x .4", but I'm thinking I may actually slightly increase the size to make it easier to assemble.
I believe this will for once and for all put to bed the issues occasionally encountered with loading on the R2LC serial data signal.