Large Scale Central

IR Switch for Crossing Signal

Electronics
#1

My basement hobby room overhead layout is a bit of a hodgepodge. A friend gave ma a 1:1 single red signal light. I repaired it, replaced the bulb with a 12V RV LED bulb powered by a flasher circuit based on a 555 timer, and mounted it beneath the overhead track.

I ordered one of these IR Sensor Switch/Relay

and wired it to turn on the timer. With the delay set for a few seconds it turned the signal on when the train passed and went off a couple seconds after it passed. After about 4-5 cycles now it stays on constantly. When power is applied the relay turns on and stays on. Contacting the seller wasn’t much help. A replacement unit acted exactly the same.

I tried isolating the TX from the RX by placing a short piece of opaque plastic tubing over the TX but no change. I have another unit but am afraid to try it until I know what’s wrong.

Has anyone tried one of these or have any suggestion for troubleshooting?

Harold Wilson

#2

so the relay is rated pretty high on the contact capacity, so the relay is fine.

what are you using to power this circuit? is your supply solid?

Greg

Greg

#3

On the bench I used an old router power supply rated 12V 1A. On the signal I have 2 of those large 6V dry cell lantern batteries in series. It acts the same both places.

v

#4

so power should be no issue… so the first unit worked for 4 or 5 times… the second unit did the same or failed to operate properly at all?

Greg

#5

Yes, both acted the same, operated normally 4-5 times then they’re always “on”, that is the relay is always energized as if it has detected movement. If I power it off then power it back on the relay energizes as soon as power is applied and stays on. If there’s no movement the relay should de-energize when the timer setting is satisfied.

#6

It sounds like there is a capacitor across the relay and after a few pulses, it charges up enough, and holds charge, to keep the relay active. A big value resistor from the relay’s + to ground may be enough to bleed this current off and restore normal operation.

#7

I looked at the back of the board with a magnifying glass (seem to need it more often nowadays) and looks like there is a 10,000 ohm resistor on the relay primary to ground. Then I noticed a cracked case on the transistor connected to the relay primary. I next removed the second unit to check it. No cracked case! I retested it on the bench and it worked. Placed it by the track and cycled it a couple dozen times and it still works.

What I think I did: When I placed the second unit on the track I hid it in a structure with a window grill between the TX & RX sensors. I’m guessing this interfered with the signal.

I broke 2 of the basic troubleshooting rules. 1) Make sure it fails twice before condemning the part. 2) Change only 1 thing at a time (I made a slight change in the location on the sensor when I installed the second unit).