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    Microcontroller Project IR Tx and Rx

    hello,
    i am making a object detector using infra red i was informed by my professor that if it is not modulated then false triggering will occur
    now i understand what modulated infra tx and rx is but i need
    the circuit diagrams for both tx and rx circuits
    thanks for the help

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    Re: Microcontroller Project IR Tx and Rx

    What the professor means is that if you ONLY looked for IR light arriving at the detector, you would see false signals from other light sources in addition to the one you want.
    The trick used is to modulate a carrier signal at the IR TX and check for the modulation at the RX, any signal not at the correct carrier frequency can then be rejected.
    It works like this: Instead of just carrying data by turning the IR LED on and off (like sending Morse code with a flashlight) you turn a carrier on and off instead. The carrier is a much faster flash rate than the data, typically around 38,000 times per second. For example, instead of sending:
    <on><off>< on ><off><on>< off >
    you send
    <flashing><off>< flashing ><off><flashing>< off >

    At the receiver, you filter the detector signal so that only the carrier (flashing) frequency is used and everything else is ignored. This gives good rejection of unwanted interference.
    Some more information is at: ATV-Projects Infra Red Remote Controls

    Brian.



    •   Alt7th December 2010, 16:01

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    Re: Microcontroller Project IR Tx and Rx

    No offence but I already know the theory I even know that by selecting selective values of R and C in LM555 timer the modulated signal can be generated and if the reciever circuit recives only those frequencies which it was designed for.
    I found the circuit of TX of infra it contains a astable vibrator what i require is the circuit of receiver side thank you



    •   Alt7th December 2010, 18:11

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    Re: Microcontroller Project IR Tx and Rx

    My apologies if I belittled your knowledge.

    Most of the modern IR detectors have optical and carrier filters built in, all you have to do is give them power and the demodulated signal appears on the output pin. It is almost impossible to find IR receivers without on-board filters these days.

    To control an LM555 astable, the method I used in the past was to drive data into the reset pin. Be careful with some variants of 555, while some can sink/source 200mA or more, there are some versions that are only rated to very low current and they will not drive an IR LED directly.

    Brian.



    •   Alt7th December 2010, 20:53

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    Re: Microcontroller Project IR Tx and Rx

    I think i should tell what i really want to build
    i am currently working on AT89s52 and i want to build a object counter the input from the IR receiver side will be fed to one of ports of 8052 nd two BCDS will be attatched such that upon falling of object in destined vicinity the bcd should say 1 nd den 2 nd den so on....
    the prograamming is done in such a way that (if p0.0 !=0) R1=R1+1
    nd den R1 will decide the output of BCD
    but where i live as you said IR receiver is not coming in pre-modulated way it comes in pair like only a RX and TX
    thats why i want the receiver circuit



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    Re: Microcontroller Project IR Tx and Rx

    I think that you are referring to an optical reflective sensor? something like this where an IR signal is transmitted, reflected off an object then then received by a photo transistor?

    If this is the case then you need to build an oscillator to drive the LED (like you said - a 555 circuit should do it) Then build an amplifier circuit to power the receiver and pass the output through a band pass filter with a centre frequency corresponding to the frequency of the TX signal.

    This application note may help you design an appropriate receiver circuit.

    This web page gives information on designing a band pass filter.



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    Re: Microcontroller Project IR Tx and Rx

    Eanema describes a reflective system where the IR source and sensor are on the same side of the object but the same principle applies if you are interrupting the light beam by passing the object between the source and detector.
    You can just use an IR LED and a simple IR sensor but only if there are no other light sources or heat sources nearby, using a modulated carrier is safe in all circumstances.

    Brian.



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    Re: Microcontroller Project IR Tx and Rx

    i have made some aplication like that. i made to detection object in front of robot. using IR LED for transmiter dan photodioda for receiver. it's work.
    using ADC input in ATMEGA16.. and compare it.. and i get value if object in front of robot and value if there no object.



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    Re: Microcontroller Project IR Tx and Rx

    Quote Originally Posted by bagusibnu View Post
    i have made some aplication like that. i made to detection object in front of robot. using IR LED for transmiter dan photodioda for receiver. it's work.
    using ADC input in ATMEGA16.. and compare it.. and i get value if object in front of robot and value if there no object.
    I had already made this project back in 5th semester. Now I have completed by engineering



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