Stefandk's suggestion of the E-B resistor has worked for me, but a better option would be to use an optocoupled logic gate (H11L1 or similar).
These work at much higher speeds than opto transistors. 115200 baud should be no problem.
How about wiring the LED of an optocoupler in series with the supply line? Current flowing in the LED will switch on the optocoupler, and the output can be used to drive your relay/PLC input. A 4N25 or 4N35 should work fine.
A simple resistor network might be a good idea to limit the current...
Lewish, Elevators use an external brake (like a car drum/disc brake) to stop the motor. This is because the motor not only needs to be stopped, but also needs to be "locked" when it is stationary, to prevent it from creeping.
Torque, if you need the motor to be locked solid while...
