Hi,
I am redesigning a circuit that detects trains on sections of 3-rail track in a large model railroad. I take advantage of the fact that the trains run on a constant 18VAC that is applied to the center rail and then to the outside rails. Because the outside rails are in common, I disconnect one rail and run it to my detector. When a train rolls onto my track, the 18VAC from the opposite side now flows through the detector wire to my circuit which is a AC/DC rectifier that puts out 12VDC when on. My current design has no logic, its a simple 12 volt output.
This is a problem when the train is only the wheels of a car that initially makes intermittent contact with the rails. The output causes the 12VDC relays that control signalling for the track to chatter and the signal indication to fluctuate between green for clear, and red for occupied.
What I would like to do is use some kind of circuit that would use a very small delay for the output to come ON, and a 1/2 second delay for OFF. As I browse the electronic advice here I see alot of references to the 555 circuit. I wonder if it could be made to automatically reset itself after the 1/2 second to be ready to turn on the output again?
The ON delay is not necessary, it could be instant ON.
Thanks in advance.
- Miles
I am redesigning a circuit that detects trains on sections of 3-rail track in a large model railroad. I take advantage of the fact that the trains run on a constant 18VAC that is applied to the center rail and then to the outside rails. Because the outside rails are in common, I disconnect one rail and run it to my detector. When a train rolls onto my track, the 18VAC from the opposite side now flows through the detector wire to my circuit which is a AC/DC rectifier that puts out 12VDC when on. My current design has no logic, its a simple 12 volt output.
This is a problem when the train is only the wheels of a car that initially makes intermittent contact with the rails. The output causes the 12VDC relays that control signalling for the track to chatter and the signal indication to fluctuate between green for clear, and red for occupied.
What I would like to do is use some kind of circuit that would use a very small delay for the output to come ON, and a 1/2 second delay for OFF. As I browse the electronic advice here I see alot of references to the 555 circuit. I wonder if it could be made to automatically reset itself after the 1/2 second to be ready to turn on the output again?
The ON delay is not necessary, it could be instant ON.
Thanks in advance.
- Miles