Wanting to build an IR trip wire.

Discussion in 'General Electronics Chat' started by Tactical Viking, May 13, 2015.

  1. Tactical Viking

    Thread Starter New Member

    May 13, 2015
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    I recently purchased a new car and started parking it in the garage. The only problem is that I have a hard time telling if I have pulled far enough in to shut the garage door. I want to use an IR trip wire with a visible LED to tell if I have pulled in far enough. have done some research and found that using the LEDs from a remote firing at an IR sensor will be my best bet. I already have a 5V power supply from an old phone charger that I am going to use. I am really new to designing my own circuits, but I do have some experience with soldering and following diagrams.

    Wiring the LED is simple enough. Just a power supply, an oscillator, a resistor, and an IR LED

    Wiring the receiver is where I am confused. I know that I will need various resistors and transistors in the circuit. I am imagining something like this assuming everything is properly powered and grounded: the output pin of the receiver is wired to a transistor/relay that sends power to a visible light LED. Would this work?

    My question: What type of transistor or relay do I need to use to make the visible light LED light up? And does this schematic sound correct?

    I don't want to use any microcontrollers or anything that needs programmed. This is a really simple thing to design, I just don't want to mess anything up.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    There are several complicating factors:
    1. The IR beam will diverge as the separation between the IR transmitter and receiver increase.
    2. The intensity of the beam on the receiver will go down by a factor of 4 for a doubling of the separation.
    The problem is to design a transmitter with enough output energy to bridge the gap, and a receiver sensitive enough to pick it up. Using a modulated beam might improve the design.
     
  3. RichardO

    Well-Known Member

    May 4, 2013
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    index.jpg

    Doesn't need batteries. ;)
     
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  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I have used the tennis ball on a string, and it works just fine.

    The best IR trip wire I have found is the safety beam across the bottom of a garage door. I have picked up several of the garage door senders and receivers at Habitat for Humanity Thrift Shop for a couple of bucks. I have figured out how to deploy them as as beam-break detector. These work quite well in varying ambient light conditions over some impressive distances (>30 ft inside my hangar). Write back if you want the secret on how to use these for this purpose...
     
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  5. ian field

    Distinguished Member

    Oct 27, 2012
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    One solution that might make things a bit easier; find a scrap set top box - or pretty much anything that uses a remote handset.

    There's usually some form of front panel strip of PCB, generally with any buttons and/or display module - the IR sensor is a little 3-terminal device, sometimes they have a wrap around tin-plate shield, but you can always see at least the lens, which looks black but has a certain redness if you catch the light with it.

    There's hundreds of types, and I've never seen a part number - so you have to do a bit of track tracing to identify the pins. The GND is usually the easiest, and if there's a shield that will also be connected to it. The +5V pin is almost always fed by a 100R resistor and is decoupled by a small electrolytic. That only leaves the signal pin, a thin track that wends its way across the board till it gets to a connector.

    Most of these sensors contain a pass band filter, usually 38 or 40kHz, so its quite handy if you have the PCB from the matching remote - although I built a remote tester with one of these sensors and it responded to every romote I've pointed at it. Most buttons on remotes only send the code a set number of times - you have to release the button and press it again. It would probably be easier to rig a 555 to puls a IR-LED and tweak it for an output from the sensor.

    The sensor output is usually just a common emittor transistor with a pull up resistor, it can't handle much current - I'd suggest driving the gate of a small logic level MOSFET.
     
  6. Tactical Viking

    Thread Starter New Member

    May 13, 2015
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    I would use this method but I keep dogs in the garage and I don't want them to tear it up and make a mess
     
  7. Tactical Viking

    Thread Starter New Member

    May 13, 2015
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    This was my original idea but I don't know how to mod the sensors. Could you enlighten me please?
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Here is the magic info about those Garage door safety sensors. Power is ~6Vdc, fed through a 51Ω resistor (see the schematic). To test your sensors, wire the Tx in parallel with the Rx. Blk-Wht wires are positive through the 51Ω to 6Vdc, Wht wire goes to 0V.

    If you power them up and aim the Tx at the Rx, you should have an amber LED on the Tx and a green LED on the Rx. If you block the beam (or misalign them) the green LED goes off. You can use the green LED as an indicator that beam is not broken... Do not try this without the 51Ω resistor.

    The way the Rx communicates with the garage door operator (and the reason you cannot simply defeat the safety sensors with just a jumper) is that while the Rx is receiving the beam from the Tx, the Rx pulses the Blk-Wht wire to ground (effectively momentarily shorts it) for ~0.4ms every 6.4ms.

    Obviously, the garage door operator is looking for this pulse train. The door will not go down if it not receiving pulses. The 6Vdc supply and 51Ω resistor R1 is actually inside the operator. If you are testing the Rx/Tx, you have to provide the 6Vdc and the 51Ω separately.

    In the complete circuit below, I'm using a 555 wired as a re-triggerable one-shot to detect that the pulses stop when then beam is broken. Pin 3 (out) of the 555 is high as long as it is receiving pulses, and goes low ~25ms after the last pulse is received after the beam is broken.

    The 555 out pin 3 can sink ~200mA, so it can drive a small relay, or a big LED or ??? For power, get an old wall-wart that puts out ~6Vdc. The sensors seem to work ok on 5 to 7Vdc.

    LMBB.gif BeamSensor.jpg Pulse.jpg
     
    Last edited: May 14, 2015
  9. Tactical Viking

    Thread Starter New Member

    May 13, 2015
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    Thank you MikeML. I just looked at the safety sensor on my garage door and noticed that the green LED turns off when the beam is obstructed. Could I just pull that unit apart and extend the leads for that LED?
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Likely. Or just mount the Rx so you can see it from the car. Just remember that you need to add the 51Ω resistor.
     
  11. Tactical Viking

    Thread Starter New Member

    May 13, 2015
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    What is the point of the 10μ capacitor? I am having troubles finding this small of a capacitor online
     
  12. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    10uF? Digikey shows 408 different 10uF 10V to 25V aluminum capacitors in stock?

    108 if you filter out the SMD (surface mount) ones.

    It is used a local bypass on the 555 power pins. 555s are notorious for generating transients when they switch states...
     
    Last edited: May 15, 2015
  13. RichardO

    Well-Known Member

    May 4, 2013
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    Ah, dogs and tennis balls in the garage does sound like a bad mix. :eek:
     
  14. upand_at_them

    Active Member

    May 15, 2010
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    I can tell I've pulled into my garage fully when my car's B pillar aligns with a rake hanging on the wall.
     
  15. dl324

    Distinguished Member

    Mar 30, 2015
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    Some low tech solutions, no power or batteries needed...

    Before I received some things to put on the floor as a gift, I put a 2x4 on the floor. I've also used the line-up-something method...
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    What happens if someone borrows the rake and puts it back on pegs deeper into the garage?
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
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    If there's mains laid on the solution can be much simpler than discussed so far.

    A filament bulb run at under half its rated voltage will emit plenty of IR, and last a very long time.

    There's no need for elaborate pulse sensing at the IR sensor as long as its well shielded and can only see the bulb, usually the photo-transistor is just mounted in the back end of a small plastic tube that's been painted flat black.

    A photo-Darlington would probably drive a LED with little or no additional amplification.
     
  18. upand_at_them

    Active Member

    May 15, 2010
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    I know which peg it is.
     
  19. Farley

    New Member

    Jul 9, 2015
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    Found this site/thread because i was looking for a way to implement a garage door safely beam form and older garage door that was just replaced.

    Interested in the "Secret"
    I would like to use the beam to trigger a sprinkler valve that would stay on for about 10 seconds ( that would allow flow of water to a few strategically placed sprinkler heads to run off unwanted animals)
     
  20. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Post #8, this thread.
     
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