Given the thread topic of using a servo with an Arduino, here's another idea for controlling conventional track voltage to smooth out speed variation going up/down grades and so on. If an Arduino is involved to select the number of diode-drops in some kind of sequence, why not use a standard servo with an Arduino to turn the voltage control knob of an MTH Z-controller transformer?
This allows smooth ramping of the increasing/decreasing voltage rather than finite jumps based on the diode drops. The voltage will be proportional to the servo.write(x) value. If you power the entire loop with the output of the Z-controller, this eliminates having to create isolated power blocks fed by different taps of the diode-dropping string.
Then, since even the entry-level Arduino provides 2 servo control outputs, you can use the 2nd servo to trigger both the Whistle/horn and Bell buttons. Since the two buttons happen to be adjacent on a Z-controller, a servo.write command of >90 will swing the arm toward the Bell button, a servo.write command of <90 will swing the arm toward the Horn/Whistle button, and servo.write(90) will be the idle position.
Note that an Arduino would be perfect for sequencing timed button presses such a short and long horn triggers to automatically generate grade-crossing warning blasts. Or, if you operate MTH conventional engines, the Arduino could sequence the Bell and Horn/Whistle buttons to activate features such as firing the coupler or, as shown in the video, activate "PFA" Passenger-Announcement using the Bell-Horn-Horn sequence.
With servos available for 99 cents and entry-level Arduino controllers for $2-3...
