pls help me "IR 38khz transmitter"

Discussion in 'The Projects Forum' started by ericyeoh, Aug 2, 2009.

  1. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    any one can help me for this circuit below?
    is that any problem with this circuit in the link?
    can anyone tell me?
    http://www.electronicsforu.com/EFYLinux/circuit/nov2004/CI-05-Nov04.pdf

    the circuit never mention what type of IR LED be use, so i just simply buy and use it, anyway is it possible the problem of transmit?

    I saw some forum dicuss by putting 2 IR LED at the output (pin3) of 555
    what for ??
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    Thx for reply
    by the way the market at here dun hv 1738 only have 4838 and 4138
    1st.question
    if i use the component i mention above can it work?
    2nd question
    if i'm using 4838 and 4138 which IR LED should i use to match it?
    pls do help me!
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The TSOP4138 and the TSOP4838 will work with the same IR emmitter (LED).

    Greetings,
    Bertus
     
  5. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    oh, ic great!
    1 more question my frd, if my market here do not hv SFH405,
    for the IR emitter, is that i need the characteristic of wave length = 950nm?
    forward currect,forward voltage and the viewing angle no need to care right?
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You can also use one of the following IR emiiters:
    SFH4110
    IRL80A
    CQY36N
    CQY37N

    Greetings,
    Bertus
     
  7. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    You are so good man!
    i will construct my circuit once all the component has arrive and i will test it, if there are any errors occur i will ask for your help agian, thx dude!!
     
  8. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    omg i need help agian
    but by looking the circuit it say it's to be 38khz,
    from the formula f =1.4/(R1 + 2R2) × C1
    substitute all the value inside the frequency is about 34khz only what?

    if i change the R2 = 18k , the frequency will close to 38khz!
    can give opinion?
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have found a simple calculator for the NE555 (one of the many):
    http://www.g8ajn.tv/technical.htm

    38 kHz will be at 18500 Ohms for R2.

    Keep in mind that capacitors are not very accurate.
    They can have tolerances upto 20 %.

    When you want more stable signal use styroflex or siver-mica capacitors.
    The use of metalfilm resistors will also help.

    Greetings,
    Bertus
     
  10. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Try to use the minimum value possible for capacitors which have a greater tolerance. Or you could try resistors and capacitors suggested by Bertus.

    Another way is to set up the circuit with the current components and measure the frequency on CRO. Then reverse claculate the constant (1.4) to adjust for the capacitor tolerance. After this do not change the capacitor and use the new constant for calculations. All this is not quite practical but good to know. !!
     
  11. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    bertus
    i just want to confirm,u mean the capacitors 0.001 micro should be use in styroflex or siver-mica type right?
    Then the resisor metalfilm resistors -->18k or 20k or variable resistor?
     
  12. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Yes, for the 0.001 μF capacitor you can take a styroflex or silver-mica.
    Those will be more expensive than the ceramic.
    You can take for the resistors 1K and 18 K metalfilm resistors.
    You can place a potmeter of 5K in series with the 18K for adjustment.

    Greetings,
    Bertus
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    This is the second recent thread that uses that very old circuit with its poor performance. Must be school homework.

    The IR receiver doesn't work properly when it receives continuous 38kHz of IR. Then it reduces its gain. It expects to receive bursts of 38kHz IR pulses as shown in its datasheet.

    The IR LED has rather low current pulses.
     
  14. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    well the original 38khz circuit is done and test the distance can only acheive to 60cm. the receiver i using TSOP4138 and the IR emitter LED i just simply buy 2mm size.
    The current through the LED is 65mA, wonder why the voltage through the LED only 0.7V.
    The output of the 555 is rather low 2.1V only so the voltage across the 22ohm resistor is measure ~1.4V
    But i replace another type of IR emitter, the distance can receive is defferent. but also cannot radiate more than 60cm
     
  15. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,672
    899
    You need to modulate the emitter signal. See Figure 7 in the datasheet.

    When it receives a continuous 38KHz signal, it assumes that may be interference and decreases its sensitivity.

    You can add the modulation with a second 555 or use a 556 for both the 38KHz and modulation.

    Here is a schematic for something I made a few years ago to modulate the 38 KHz carrier.

    [​IMG]

    John
     
    Last edited: Aug 18, 2009
  16. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    TQ for sharing info i will try TQ TQ
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    You cannot measure the 38khz voltage of the IR LED or of the 555 with a DC voltmeter or with an AC voltmeter. You must use an oscilloscope.
     
  18. ericyeoh

    Thread Starter Active Member

    Aug 2, 2009
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    i;ve try to reflected the infrared signal by using a mirror to the TSOP receiver, by it failed..
    Guys..Any opinion on how can i reflect the signal and the Receiver still can get the signal?
     
  19. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It can be the glass in the mirro weakens the signal to much.
    You will need a reflective plate without the glass in front.
    In IR spectrometers the mirrors do not have glass, but are damped on a surface.

    Greetings,
    Bertus
     
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