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IR Detection Circuit

Discussion in 'General Electronics Discussion' started by bxdobs, Jan 14, 2016.

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  1. bxdobs


    May 11, 2014
    - Supply: 9V Battery with LP2950 5V regulator
    - wake up a PIC 10F206 (using weak Pull up) with a low power (< 200 uA) 38KHz IR 940nM IR detector

    Using an op-amp or comparator to do this appears to require too much standby current > 1 mA

    Using LTSPICE models based on a minimum 45nA source current measured with several different IR detectors ... both NPN and IR Diode Detectors were measured ... the source current is dependent on distance from the IR Source ... measured at approximately 3' to 4' from the source. ... current was calculated based on a 5V Source and 20M series resistor ... Voltage measured with x10 scope probe and ac coupled 50mV/Div

    Circuit 1

    Circuit 2

    In both circuits the LTSPICE models show the saturated switching occurs around roughly 45nA (the IR detector is simulated with a Current Source)

    Circuit 1 doesn't appear to work in real life ... perhaps the 2N7000 LTSPICE model needs tweaking

    Circuit 2 is so sensitive it is affected by sunshine ... when the sun is blocked the circuit does appear to work the way the LTSPICE model predicts

    Any suggestions would be appreciated

    Attached Files:

  2. AnalogKid


    Jun 10, 2015
    In circuit 1, what is the gate voltage? A 2N7000 requires at least 2 V to start to wake up.

    All IR circuits have trouble with sunlight, which is why all of those IR remote controls send digitally coded IR pulses, something the receiver can differentiate from sunlight, incandescent light bulbs, and people.

  3. bxdobs


    May 11, 2014
    Didn't measure the gate voltage on circuit 1 ... the sunlight pulled circuit 2 high continuously so even the 38 KHz signal I was using to test it with wasn't seen

    The wife went and purchased one of those robotic vacs which uses a 38KHz pulse to detect objects so it doesn't bump in to them ... I built a virtual wall which chews up batteries so was hoping to just detect when the device was close by and turn the vw on for a short period of time.
  4. chopnhack


    Apr 28, 2014
    The 9V battery typically only has about 500mAh of useful lifespan. Can you use 4x AA or AAA instead?
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