This project was produced to allow testing of DCC Decoders to determine the range of pulse lengths that the decoder accepts.
Nominal DCC pulse lengths (half-pulse-lengths, in fact) are 58us for a '1' bit and 100us for a '0' bit. DCC++EX uses 58us and 116us, to simplify the pulse generation code. Decoders are, according to the NMRA and RCN specs, required, as a minimum, to accept 58us +/- 6us as valid '1' bits, and anything between 90us and 10,000us for valid '0' bits. I wanted to see exactly how well commercial decoders adhered to this and how much additional tolerance they might allow.
The program is a modification of the DCC++ Classic CommandStation, since this is not constrained to generating '0' pulses that are twice the length of the '1' pulse, as DCC++EX is. All that remains is the code for generating DCC signals in response to commands sent over the serial line. All that has been added is a command that allows the pulse lengths for '1' and '0' bits to be set on-the-fly. Only the Arduino Mega is supported.
The Classic programming mode is unfortunately not reliable enough for testing the pulse width; consequently, it is recommended that tests are performed by using the function commands and throttle commands. Change the DCC pulse length, and then modify the speed of the engine or trigger a sound or LED function, and see whether the change is effective at the current pulse length.
The new command is in the form <l 1|0 n> where the first character is lower-case 'L', and n is an integer.
So to set the nominal pulse lengths of 58us and 100us, you would send <l 1 58><l 0 100>.
To increase the length of the '1' pulse by 2us, send <l 1 60>.
Example commands:
<l 1 58><l 0 100> Set 'nominal' pulse lengths 58/100us
<t 1 3 50 1> Set throttle to 50 for loco 3
<l 1 40> Set '1' bit to 40us
<t 1 3 0 1> Try to stop loco