Page 2 of 2 FirstFirst 12
Results 11 to 17 of 17

Thread: How to generate bursts for IR Detection

  1. #11

    Default

    thanks docel

    i m trying both TSOP1738 and TSOP1333 whichever works but seems neither working for me.

    After searching through forums i got some idea about how to create bursts.But the problem is that i am not so sure about the calculation part (frequency and all).

    I have to use another 555 generating a frequency of 3.8 Khz (or it should be 3.8 Hz i dont know) and connecting its output to the trigger of another 555 which is generating 38 khz.

    but confused whether the output of the first 555 (3.8Khz) should be inverted or directly connected to the trigger of the second 555 ??

    but above shobhitkukreti have written that the output of the both 555 timer should be ORed ???

    Confused .....guys please help me.

  2. #12
    Senior Member T-1000
    Join Date
    Mar 2005
    Location
    Bangalore
    Posts
    728
    Blog Entries
    7

    Default

    As far as the TSOP is concerned....how to check whether its working or not.
    .. Use a TV remote, fire it at the TSOP, and check the output to see if the TSOP is working.



    .
    The output goes low when it detects the IR for the very first time (when the IR is aligned in the direction of TSOP not any reflection stuffs..) and then the output remains high even if the IR is continuously aligned to the TSOP.
    .. you need to turn the 38Khz on and off periodically, at a lower frequency. a 555 is held in reset when the reset pin is low. Wire two 555 in astable mode, one with 38 Khz and other with a lower frequency. connect the output of the lower frequency one to the reset of the other one. That will be enough.

    By using a logic gate, you are unnecessarily adding an extra chip. Also, it should be an AND gate. (You dont want the IR to be ON most of the time..) I guess shobith meant an AND gate.

    Also, many a times, TSOP will work with continuous signals. It has worked with me most of the times, but there were times it did not. The problem comes when you have all your PCB set up, working, and one fine morning , you replace your faulty TSOP just to see that the new one does not respond to continuous signals.

    Yes, it works mostly, but its always better to trust the manufacturers data sheet, as doc said.

    Good luck.
    .... I didnt do it ! ....

  3. #13

    Default

    hey.. sorry.. and gate could be used, was thinking of something else then, i apologise, and you need to read the datahseet of 555 and understand it's working, it is not that tough,


    assume : _ _ _ _ _ _ _ _ _ 38 khz freq, where _ is high o/p and empty space is o/p low

    this is your low freq signal .____ _____ ______

    Basically untill the low freq signal is high the 38khz signal will be received as output on your LED, however as soon as the low freq signal goes low, the 38khz signal will not be received at output.

    That is how you will receive bursts of 38khz

  4. #14

    Default

    Just one more question....regarding the timer and all....I have made one 555 timer to generate 3hz at 9% duty cycle to trigger another 555 timer generating the 38Khz at 52% duty cycle.

    As u said that the TSOP will only give O or 1( Vcc) as output but I am not getting that instead the voltage at PIN 3 is continuously changing from around 2.8 V to 2.4-2.1 V at a very fast rate.

    And also..the LED connected to PIN 3 of the TSOP is blinking even if the IR is covered from all side. Don't know why ??So can't find out whether the IR is getting reflected from any obstacle...or not bcoz even in the absence of obstacle it remains in that state i.e blinking (opposite to that of IR -active low).

    Do I need to change the duty cycle of any 555 or its fine ??Do i need to increase the duty cycle of the lower frequency timer ??

  5. #15

    Default

    Quote Originally Posted by shobhitkukreti
    hey.. sorry.. and gate could be used, was thinking of something else then, i apologise, and you need to read the datahseet of 555 and understand it's working, it is not that tough,


    assume : _ _ _ _ _ _ _ _ _ 38 khz freq, where _ is high o/p and empty space is o/p low

    this is your low freq signal .____ _____ ______

    Basically untill the low freq signal is high the 38khz signal will be received as output on your LED, however as soon as the low freq signal goes low, the 38khz signal will not be received at output.

    That is how you will receive bursts of 38khz
    what should be the low frequency ? Will 380 Hz do the work or i need to lower the frequency ??

  6. #16

    Default

    For reliable operation burst length> 10cycles/burst. So think about this way the ON Period of Lower frequency should allow at least 10 cycles of 33/38khz. It is just like switching the 33/38 khz frequency circuit ON/OFF very rapidly but lower than 38 khz to allow at least 10 cycles.
    According to the circuit 3hz should also be fine, try 1.8khz or lower

  7. #17

    Default

    The output of TSOP is average value which you are getting. read the post by docel, it is pulsing low and voltmeters are not good enough to catch that pulsing low that quickly

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •