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Thread: Detection of obstacles by infrared

  1. #1

    Default Detection of obstacles by infrared

    I have to detect an wooden obstacle placed at a distance of 5 to 12 cm from my robot. I have made a circuit using 555 timer as astable multivibrator with Ra=1K, Rb=18k and C=0.001microfarad to generate a frequency of 38KHz for ir ked and tsop1738 as ir receiver. But still I failed to get a desired output. Please help me with an working circuit diagram.Please also tell me about the placement of ir led and detector for the detection.

  2. #2
    Super Moderator T-1000 docel's Avatar
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    Have you read the Data sheets??
    Tsop's dont work with continuous signals!
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

  3. #3

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    Also, with 555 timers always check on oscilloscope the frequency you are getting.

    Most probably, the designed frequency won't match with the actual frequency. Use a pot to adjust the frequency to 38k and then use the required resistor (use less tolerance components).

    Better still use a microcontroller (if possible) to generate the frequency. Will help with the bursts as well.

  4. #4

    Default Continuous signals

    Dear docel

    Please explain me what is the meaning of continuous signals.I mean how do I get "burst" signals(what is the circuit) I do not know much about the working of the tsop. And please give me a diagram of an working circuit to try my hands on.

  5. #5

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    Docel,

    I got some Vishay TSOP1738 and some Chinese made cheaper versions of the TSOP. While the Vishay module seems to need the "burst"s, the Chinese versions respond fine to a continuous 38kHz square wave. I decided to go with the Chinese ones as
    • * They are cheaper
      * It is easier to generate a continuous square wave rather then a wave with bursts


    Yes I do realise that I am rendering myself susceptible to interference from some lighting sources and sunlight . It is a trade off.

    A

  6. #6

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    Docel,

    I have a further question. Given that the TSOP does not respond to continuous signals, Why do a lot of people design TSOP based proximity detectors where the emitter is driven using a 555 based Oscillator ?

    I took one such circuit and tried to use it with a TSOP. The TSOP responds, but immediately goes back to dormant state. It is then that I actually read the data sheets ( ops: ) and realised that I needed to generate bursts.

    What is the rationale behind using a 555 based osc to drive the TX ?

    A

  7. #7

  8. #8

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    The other discussion is from 2005! I should do more thorough searching before posting. Thanks King.

  9. #9
    Super Moderator T-1000 docel's Avatar
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    Thats agood question Arcane, and thanks Pratap for remembering that post

    Now, all data Specs regarding the TSOP holds good ONLY for 17XX family by Vishay/ Telefunken and other European and American Modules. The Chinese modules are not Direct equivalents but "functional " equivalents only and do not share the TSOP17xx specs. There are numbers like HRM380017 and behave weird...
    but - maybe they are desirable for the 555 non-burst scheme. :wink:

    Another thing: The Circuit uses a BC107 NPN. This means the O/p is ON all the time until "IR detect" , remains on for some time till the base cap. discharges. The entire setup is for Pulse detection rather than any measurement or Data decoding (momentary). It is appropriate to use a PNP transistor for normal IR Detect= O/P ON.
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

  10. #10
    Mamadshah
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    Default Perfect! Try this sites:

    edited

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