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  • Topic: IR Switch for Crossing Signal

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    • September 25, 2019 10:06 PM EDT
      • Telford, TN
         
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      IR Switch for Crossing Signal

      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

       

       

    • September 25, 2019 11:05 PM EDT
      • Be Nice or STFU
         
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      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

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    • September 26, 2019 7:54 AM EDT
      • Telford, TN
         
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      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

    • September 26, 2019 12:07 PM EDT
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      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

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      Be sure­ to visit ­my site, l­ots of tec­hnical tip­s and modi­fications,­ and you c­an search ­for topics­ and key w­ords.


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    • September 26, 2019 1:09 PM EDT
      • Telford, TN
         
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      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.

    • September 26, 2019 2:06 PM EDT
      • Santa Ana, CA
         
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      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.

    • September 26, 2019 6:38 PM EDT
      • Telford, TN
         
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      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).

       

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