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Infrared detection

  1. Apr 10, 2017 #1
    I made the following circuit for 38kHz infrared receiver TSOP38238 to increase the detection range above 10 meters. i was quite happy to see the range is more than 20 meters with TSAL 6100 LED. but i am facing a problem, my circuit works like a relay circuit. i have to wave my hand in front of receiver or transmitter so it can detect. Any help will be appreciated. thanks
  2. jcsd
  3. Apr 10, 2017 #2
    Is Q1 your pick up device?
    I cannot see anything marked TSOP38238 on your diagram.
    Where is the output?
    What do you want to happen when IR is detected?
  4. Apr 10, 2017 #3
    Thanks for replying.....
    Here is my receiving circuit
    i want to build a self charging robot which can detect its charging station and makes it way to the charging station...
    the receiver diagram showed above is just for understanding purpose. in real circuit i used LM324 comparator between Q3 and Arduino. LM324 comparator provides High or LOW to Arduino, and then Arduino operates LM293D. the main purpose is to detect signal and get to the Charging station. i have placed three TSOP38328 receiving circuitS on top of my robot, one for for turning left, one for right, and the middle one to drive robot straight. and my charging station is my TSAL 6100 LED transmitter.
    Thanks again for taking interest.

    Attached Files:

    Last edited: Apr 10, 2017
  5. Apr 10, 2017 #4


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    The way you have set up your LM555s is somewhat unusual. What was you thinking?
    The TSOP38238 is designed to detect short bursts, not continuous trains of pulses.
    You need to produce short bright bursts of 38kHz pulses rather than a continuous stream.
  6. Apr 10, 2017 #5
    Ok let me explain, i made a circuit with only one Lm555cn, which did work but i didnt get a distance more than 3 meters. i added up a BC327 transistor on the out put of LM555 which increased the distance to 5.5 meters. in the distance of 5.5 meters my robot works fine.it detects the infrared signal and makes it direction accordingly. i wanted to increased the distance so i used another Lm555cn and double modulated the 38kHz frequency as can be seen in the first picture i uploaded, which increased the distance to 20 meters but with a problem that i have to move my hand between two circuits so they can detect.
    thanks for taking interest.
    Actually i didnt want a double modulated signal, all i wanted to supply 200 mA to TSAL 6100 for less than 100us (as the data sheet of TSAL 6100 says, Forward current = 100mA and Absolute Maximum current = 200mA for Tp = 100us)...Tp is Pulse High....thats why i am using the second Lm555 for switching purpose.
    one thing more the circuit i made with only one Lm555 and Transistor BC327, i am providing 170mA to LED, but the range of distance didnt go more than 5.5 meters
    Last edited: Apr 10, 2017
  7. Apr 10, 2017 #6


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    Staff: Mentor

    To me, Q3 looks backwards in this circuit, and I also don't know why you would use a PNP transistor for Q3...

    And C1 looks misplaced. Why would you snub your output so hard before amplification?
  8. Apr 10, 2017 #7
    TSOP 38238 is an Active Low device , that is the reason i am using a PNP transistor for Q3
  9. Apr 10, 2017 #8


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    Staff: Mentor

    I'm not sure that explains the choice, but whatever. What about the backwards (upside-down) configuration and the strange capacitor placement? Was this from some Application Note from the IR receiver module?
  10. Apr 10, 2017 #9
    yes this from TV IR receiver module which i found from following website.
    to be honest i just noticed the upside-down configuration..and my receiver circuit does work fine without C1....
    thanks for highlighting the upside-down
  11. Apr 10, 2017 #10


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    Staff: Mentor

    Yeah, a BJT will work upside-down, but with reduced gain, generally. From the application description at the link, it looks like the capacitor was used to slow the response down (rectified sort-of) so that you get a signal that can drive the LED. They were not going for real RX speed in that circuit.
  12. Apr 10, 2017 #11


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    If you make the circuit over sensitive then it might pickup ir bouncing of walls etc making it hard for the receiver to work out where the signal is coming from. Bit like it being in a room full of mirrors?
  13. Apr 10, 2017 #12


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    Can you show us a schematic as your set up is now? The schematic you have in the OP is using the transistor in an unorthodox manner. You also say that the receiver circuit is actually something totally different than the posted schematic. Please show that as well.

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