May 2015 Occupancy Detector

Model Railroader General Discussion (Model Railroader)
1

I enjoyed Larry Puckett’s article about DCC and occupancy detectors.

I’m an old Electronics Engineer who was taught about current flow in circuits rather than electron flow. It took me awhile to be comfortable with the circuit description that Larry provided and I needed to rethink in terms of current flow to be happy with it and confirm that the circuit will work just fine.

One question that I have is the -9VDC at the bottom of figure 4 on page 57. Based on the text description of the circuit being powered by 9 volts should this be a ground connection rather than -9VDC?

It would be feasible to replace the relay with a couple of transistors to drive LEDs in the signal.

Regards - Amby N.

2

Rather than post this in the General Discussion part of the Forum you might consider re-posting it in the Electronics and DCC portion – the guys who know might more likely hang out there.

Dave Nelson

3

I think is intent is a 9 volt source. I use a similar circuit but with IR detection across the track. I didn’t use relays for my signals but I do have one detector that drops rail power with a relay on a hidden siding.

Mel