IR receiver problem (TSOP 1738)

Discussion in 'General Electronics Chat' started by dreamcatcher, Jan 14, 2010.

  1. dreamcatcher

    Thread Starter New Member

    Jan 5, 2010
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    Hi,

    I have set the following circuit

    TSOP.JPG

    I used 3 TV remote control to test it, but it didn't work.
    I know that the TV remotecontrol use 38khz signals and i tested the led and is working properly and the TSOP is new.

    please can you help me to fix this.

    thank you.
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    What do you mean by, "it didn't work?"
    Will your led light with less than 5 mA?
    The TSOP1738 usual operating voltage is 4.5 to 5.5V. Have you tried it with a supply in that range?

    John

    Added thought: The 180 ohm resistor in your supply line will cause a significant voltage drop, particularly, if the supply voltage is marginal. You might consider eliminating it or reducing it to 100 ohm with a 5V supply.
     
    Last edited: Jan 14, 2010
  3. eblc1388

    Senior Member

    Nov 28, 2008
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    As jpanhalt have told you already, the TSOP1738 only works properly between 4.5V and 5.5V.

    Secondly, the output of TSOP1738 cannot source sufficient current to drive a LED as you have connected in your circuit.

    You can connect a series resistor to the LED, one end of this resistor to +5V and the free end of the LED to the output of the TSOP1738.

    [​IMG]
     
  4. dreamcatcher

    Thread Starter New Member

    Jan 5, 2010
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    Thank you very much, it worked by setting the circuit og chung

    thank you
     
  5. dreamcatcher

    Thread Starter New Member

    Jan 5, 2010
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    I want to buil a mobile robot that detect objects that are in its way to avoid them,
    can I use the TSOP 1738 for thi purpose?
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You will need a modulated IR led as a transmitter.
    The frequency must be about 38 kHz.
    What distance do you want to detect?

    Greetings,
    Bertus
     
  7. dreamcatcher

    Thread Starter New Member

    Jan 5, 2010
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    Hi,

    I want it to be about 10in.
    I found a lot of oscillator in the web, which one do you advise me to use for this purpose?

    thank you for the reply
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Take a look at the schematic in the attached PDF.

    Greetings,
    Bertus
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    The circuit from India does not use bursts of 38kHz pulses so the AGC in the receiver will reduce the gain making the range very short.

    The receiver's AGC reduces the gain when the 38kHz pulses are continuous because compact fluorescent light bulbs cause continuous 38khz pulses and the receiver reduces their level which is interference. Remote controls transmit their data in bursts of pulses so the gain remains high.
     
  10. eblc1388

    Senior Member

    Nov 28, 2008
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    AG's comment on using 38KHz pulses is well worth consideration.

    The IR receiver's gain is very high, so high that it will detect 38KHz IR pulses tens of feet away. In my living room, I can control the TV even if I points the remote control backwards, or in any direction.

    The main point is not to allow the IR detector to consider a wall or object ten feet away as an object nearby and moves away.
     
  11. rvm.karthi

    New Member

    Dec 29, 2009
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    Hi is there any option to check this TSOP is working good os faulty...?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    When it is powered from the RC circuit shown in its datasheet, its output goes low when it receives 38kHz IR pulses. When the 38kHz pulses are transmitted in bursts that are defined in the datasheet then the range will be maximum.
     
  13. dreamcatcher

    Thread Starter New Member

    Jan 5, 2010
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    0
    Hi,

    I've set the following circuit to check the distance that can recieve the TSOP, I've made pulsses with the PB in order to keep the gain high.

    But unfortunatelly even like that i was getting a short distance,
    by doing this i thought that I was supposed to get better results since the AGC keeps the gain high.

    when i try with remote control the tsop can receive from any place.

    where is the problem?

    thank you.
     
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  14. Audioguru

    New Member

    Dec 20, 2007
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    Your 555 circuit sends continuous 38khz, if it is at 38kHz.
    Like I said in my last post when the 38kHz IR is continuous then the TSOP1738 turns down its gain because interference is continuous. You must use a second low frequency 555 to cause the 38kHz oscillator to make bursts of 38kHz as described in the datasheet for the TSOP1738. TV remotes send data which is bursts of 38kHz.

    The current in your LEDs is very low so the range will be short. The current is only (1.4V - 0.7V)/180= 3.9mA. TV remotes pulse their IR LEDs at up to 1000mA.
     
  15. dreamcatcher

    Thread Starter New Member

    Jan 5, 2010
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    If you see well in the drawing I'm not sending a continuous 38KHz signal to the IR led since I'm controlling it with the pusch button, I send only when i push and release in a fast way.

    and for the current, the led gets: (9V - 0.7V)/180 = 46.11mA

    the TV remote control uses only 3V.

    may be I have to use a smaller resistance to get more current for the led.

    ???????????????!!!!!!!!!!!! :s
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    You cannot manually turn the 38kHz pulses on and off fast enough. You need an oscillator to do it.
    But your LEDs are much too dim so why bother doing it?
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    Your math is completely wrong. How can the 180 ohm resistor have a voltage of 8.3V across it when it has a low current current regulator transistor in series plus at least one 1.3V IR LED or two also in series? If you have two 1.3V IR LEDs in series with a shorted transistor plus the 180 ohm resistor then the current would be (9V - 2.6V)/180 ohms = 35.6mA which it is not in your circuit.

    The current regulator has 1.4V across two diodes and the 180 ohm resistor has a transistor's base-emitter reducing the voltage across the resistor to only 0.7V.
    Ohm's Law says that 0.7V across 180 ohms makes a current of only 0.7V/180 ohms= 3.9mA that flows through the transistor and IR LEDs.

    Get rid of the current regulator circuit and replace it with a low value resistor calculated not to burn out your lR LEDs. The driver transistor and its base resistor also must be calculated for the higher current. The battery needs a bypass capacitor. Add an electronic burst oscillator at the correct frequency. Add an important supply bypass capacitor.

    Turn the 38kHz 555 on and off in bursts by its reset pin 4, not with another transistor in series with the LEDs.
     
  18. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    This is the type of thing Audioguru is describing. IC1B turns IC1A on and off at about the correct frequency.

    [​IMG]

    John

    Edit: The packet repeat is at about 833 Hz. If you could tap that out on a table, it would be of the same frequency range as a piccolo.
     
    Last edited: Feb 16, 2010
  19. Audioguru

    New Member

    Dec 20, 2007
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    A picollo plays frequencies much higher than only 833Hz. A flute and a clarinet play 833Hz.
     
  20. hgmjr

    Moderator

    Jan 28, 2005
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