please let me know this circuit.

Discussion in 'General Electronics Chat' started by jack hammer, Jan 25, 2016.

  1. jack hammer

    Thread Starter New Member

    Jan 25, 2016
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    Hellow.
    this circuit is infared receiver circuit for toy car motor.
    but i don't know function of r11,r12,C5 in this circuit.
    please let me know why use these.
    reciver.jpg
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
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    228
    C5 is a filter capacitor. It stablizes the power for the IR phototransistor to minimize false triggering due to relay switching.
    R11 is a bleeder resistor, which rapidly discharges C5 when power is off.
    R12 is biasing resistor for phototransistor X1.

    All this is just an educated guess.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    R11 & R12 forms a voltage divider to lower the 6V depending on the IR operating voltage. C5 is used to stabilize that voltage.
     
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    R12 = 560Ω
    R11 =100kΩ
    Doesn't really work as an effective voltage divider.

    I would say that R12 and C5 operate as a low pass filter to keep relay and motor noise away from the IR receiver.
     
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  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    You may be correct. :oops:

    I stand corrected, I believe.
     
    Last edited: Jan 26, 2016
  6. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    It happens, sometimes:)
     
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  7. Sonoran Desert Tortoise

    Member

    Oct 30, 2014
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    C5 is like a battery that quickly drains. R12 makes sure the battery doesn't refill quickly. That way, the power to the sensor runs out (5mA output). Then it will shut off until C5 is recharged, then fire again. These little sensors become saturated and shutdown if given a constant pulse train of IR. This designer made the sensor immune to constant pulse trains. Shutdown/recharge/restart should be fairly fast. I have no idea what he was thinking on the 100k resistor other than some type of pull down resistor for the sensor while it is "powered down". The op will have to try with/without the resistor to see what is going on.

    some newer 38k sensors are available that are immune to the constant pulse issue.
     
  8. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    No, none of that is correct.

    There is no "Shutdown/recharge/restart" cycling. Have you read the datasheet for the TSOP1738?
     
  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Wow!
    Where did you learn that ?
     
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