HELP!!about Infrared Sensor!!

Discussion in 'The Projects Forum' started by evildevil2, Mar 1, 2011.

  1. evildevil2

    Thread Starter New Member

    Mar 1, 2011
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    http://www.youtube.com/watch?v=gQk3xjOUo4Q

    i watched this vedio and want to make a switch that when somthing pass through and block the infrared emmiter with the sensor the LED light up.

    then i go with this . I seperate the infrared emmiter this is the sensor part.
    [​IMG]
    my infrared sensor and emmiter
    [​IMG]


    My problem is
    1) i cant get the LED bright enougth (it is just half as bright as it should be)
    2) the seller said it can sense 3-8 meter bt now i can only get it work in 40cm . I want at least 2M
    3) can i connect it with multiple LEDs?
    4) sould i change my sensor?
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    Your schematic shows two diodes. Why?
    The light sensor is a light dependent resistor, a photo-diode or a photo-transistor. Which one is it?

    You might have an IR photo-diode. It needs an amplifier, usually an opamp is used.
    An IR photo-diode has a black case to block ordinary light. Then it won't detect an ordinary LED well. It will detect sunlight.
     
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  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    If you are feeding the IRLED with 3 volts through 10,000 ohms, the current is only going to be about 150μamps. IRLEDS are usually rated up to 50 ma. The output varies with the current, so dropping that resistor to something more like 33 - 47 ohms will get you more range.

    That is an awfully simple series circuit. I wonder about the utility of the extra diode.
     
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  4. evildevil2

    Thread Starter New Member

    Mar 1, 2011
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    The black one is the sensor and the other is a normal LED



    sorry i am a noob about all these....i am doing this for a installation project i want to built a wall when somebody is in front of it LEDs will light on.

    [​IMG]i want to build somthing like this...
    really i am a noob...
    so how can i do this .. plz help!!
     
  5. evildevil2

    Thread Starter New Member

    Mar 1, 2011
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    i just try a 22ohms resistor , the LED did light up as it should be bt the sensor distance drop to ..like 2 cm
     
  6. wayneh

    Expert

    Sep 9, 2010
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    As you've heard, the resistor is limiting the current. The higher resistance may have been chosen, though, to be a value that enables the circuit to work. In the light, the receiver opens a circuit to ground and shuts off the LED. When dark, there is a current path thru the LED and it turns on. This switching might not work with a lower resistance value - light falling on the receiver may not turn off the LED.
    Well, that's not surprising. The seller is probably referring to a modulated emitter signal, and that allows brighter pulses AND rejection of ambient noise in the receiver stage. Your very simple circuit doesn't use those techniques that can extend range. Careful alignment of emitter-to-receiver, shading the receiver in a tube, focusing optics and so on, can all help get more range.
    There's no limit, but you'll need to be more specific about your power supply, LED specs, and so on. Do you want ALL the LEDs to light or just the ones that indicate where the blockage is? The more detail you can supply, the better answers you'll get.
    It can probably be made to work, but not necessarily in such a simple circuit. I don't think you can answer this question until you've done your testing and considered the alternatives that will be recommended to you. I think the suggestion you'll hear most is to use the sensor as a sensor, and to use a separate transistor to perform the switching of the LED power. A quad op-amp would be a good choice, as it could serve 4 separate receivers.
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
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    The current output from a small photodiode sensor under reasonable levels of illumination will be less than the few tens of mA typically required to fully drive an LED. Simply connecting a diode sensor and an LED in parallel, and returning them to the positive supply via a common load resistor probably would not do much.

    If you have got some degree of function from such a simple circuit, to me it seems likely that your detector is actually a photo-transistor (which could have considerably more output than a photo-diode).

    To make your circuit work better, you need to add some kind of amplifying device to boost the output from the detector. An op-amp may be the obvious choice, but you might be able to use a junction transistor or an FET.

    Edit: I did not take in the fact that you are trying to get metres of range! Forget about just using a transistor or two - ypu will need plenty of gain, and I endorse what the last poster said about screening the detector. You may even need to go to a pulsed system to reject the effects of ambient light - if so beware of the flicker from AC mains powered lighting.
     
    Last edited: Mar 1, 2011
  8. evildevil2

    Thread Starter New Member

    Mar 1, 2011
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  9. wayneh

    Expert

    Sep 9, 2010
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    You won't need an additional op-amp if you use a purpose-built IR receiver module. There are many modules out there to choose from, and you'll need to consider at least 3 things: 1) Make sure the wavelength of the emitting diode is within the window accepted by the receiver, 2) You'll need to modulate the transmitter LED at the right frequency for the receiver, eg. 1kHz, 38kHz, or I think some are 80kHz. Lower is probably better for a noob device, and 3) I believe most or all of these receivers will not hold a "high" output very long - they're meant to pass quick data pulses that a computer will translate, not hold a value like you want. There was a thread on this forum regarding this, in the last few months. Not sure what the outcome was.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    The get good range from the IR receiver IC the IR LED in the transmitter must be modulated with bursts of data at 38kHz. It is too much geekness for a nOOb.
     
  11. wayneh

    Expert

    Sep 9, 2010
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    Perhaps, and perhaps the whole project is a bit more challenging than the OP realizes.

    evildevil2, are you hoping to just have a line of LEDs as in your stick drawing or a "wall" as you described? How many LEDs are you thinking of using? Do you want each one to be independent of all the others, like pixels?

    Have you though about how to power all of this?
     
  12. evildevil2

    Thread Starter New Member

    Mar 1, 2011
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    i think i will use the current pair of sensor and infrared ...
    i got a adaptor 12V 1500MA i want to use it as the power source
    i want about 100 LEDs over the wall and one sensor control 5 LEDs.

    can anybody help me with the schematic diagram? and give me a specific type of op amp??
     
  13. wayneh

    Expert

    Sep 9, 2010
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    Here's a starting point to give you an idea. The LM339 is a quad comparator, and the drawing shows how you could use just one of them to switch a string of LEDs on or off depending on the sate of your input

    You'll need to figure out if you can light 4 or 5 LEDs with your power source, and what the value of the current limiting resistor ought to be. This will be true for any solution you work on.

    To adapt the circuit shown,you'll also need to figure out how to "tune" your input. I've shown a way to set a threshold reference voltage on one input, with the idea that your phototransistor input will be compared against that on the other input. You may want to switch the inputs, or you may want to compare against ground - I haven't worked those details out for you.
    Picture 2.png
     
    Last edited: Mar 2, 2011
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