Monday, June 22, 2009

Signals fixed!

After spending a couple weekends trying to get my semaphores to show yellow signals, the signals are now working. Thanks to Bill at Team Digital for correctly diagnosing my problem.

For those that care, or who have a similar problem: I was connecting Team Digital's SMC4 servo controller to the SIC24 signal controllers which I program with all the special signal logic. It turns out the servo controller expects to be driven by an open collector output - that is, the output should float up to 5v because of a resistor, but get pulled to ground by a transistor. The SIC24 uses push-pull drivers where transistors tie the output to either 5v or 0 depending on the signal intended. The push-pull output interacts badly with the SMC4 so it never lets a yellow indication get through. Disconnecting all the inputs to the SMC4 and connecting each input to ground would make the signal work correctly. Bill's suggestion was to add a diode on the red signal line. (Time to pull out my college electronics book to understand why that works.)

With that small change, I have three indication semaphore signals working wonderfully!

Now, I just need to clean up the mess of wires covering Auzerais St., and then I can figure out my next project.

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