IR Detector as a Switch

Discussion in 'The Projects Forum' started by Smijo, Nov 17, 2012.

  1. Smijo

    Thread Starter New Member

    Nov 15, 2012
    26
    0
    I'm using a Panasonic PNA4611M, which provides a steady low output when presented with steady IR energy. I need this to basically turn on a 5V power source. This 5V source will go to the reset pins of multiple 555 timers. I need the 5V source to be "turned off" when the IR detector does not "see" any IR energy. The 555 timers are "off" when the voltage on the reset pin is 0.7V. Any ideas? Thanks.

    edit: From what I understand, the IR detector outputs 0.35V when it does not detect IR energy.
     
    Last edited: Nov 17, 2012
  2. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    A few points need clarification:

    contradicts

    I looked at the datasheet and if I understand it correctly, the PNA4611M outputs a high signal when an IR signal is preset and a low signal when there is no IR signal. Do you have this set up? If yes, can you verify this?

    Assuming this is true (IR preset, output high; IR not preset, output low), you can connect the output of the PNA4611M to a transistor or MOSFET to control the 5V source or directly control the reset or trigger pin of the 555.

    So you want to send a 5V signal to the reset pins of the 555 when an IR signal is present? Put another way, if a IR signal is present, 5V goes to the reset pins turning on the 555s. If no IR signal is present, 0V goes to the reset pins turning off the 555s. Is this correct?

    If so, you can use a pull-down resistor on the reset pins - this will reset/turn off the 555s whenever there is no signal present. The output of the PNA4611M can be connected to a NPN transistor or N-Ch MOSFET and wired to the reset pin so that when an IR signal is present, the transistor or MOSFET is turned on sending a high signal to the reset pin.
     
  3. Smijo

    Thread Starter New Member

    Nov 15, 2012
    26
    0
    I do not have the IR detector yet, so I can't verify the output.

    Yes, I do want to send a 5V signal to the reset pins of the 555 when an IR signal is present. So, the 555 timers will be on when the IR detects IR light.

    I'm not sure how to use a pull-down resistor. Can you explain?

    Also, can you explain how to wire the NPN transistor or the N MOSFET?
     
    Last edited: Nov 17, 2012
  4. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Whoops, I was wrong. According to note 3 on page 1 of the datasheet, the output is high when there is no IR signal present. It does indeed go low when IR is present as you said.

    Because you want the reset low when no IR is present and vice versa, you need to invert the output of the sensor.

    I've attached a possible solution I believe will work. When there is no IR signal, the sensor will output a high signal. This goes through R1 and pulls the base of the NPN transistor high, effectively closing the connection between the collector (connected to R2) and the emitter (connected to GND).

    With the NPN "closed", GND goes directly to the reset pin of the 555.

    When an IR signal is present, the sensor will output a low signal. This will turn the NPN "off". In this case, R2 acts a pull-up resistor. That is, a high signal goes from 5V through R2 and to the reset pin of the 555, turning it on.

    R2 is needed for two reasons - 1) to prevent a dead short between 5V and GND when the NPN is on and 2) to keep a high signal going to the reset pin when the NPN is off.
     
  5. Smijo

    Thread Starter New Member

    Nov 15, 2012
    26
    0
    I've been running LTspice simulations all day, and I think I have tried that circuit and it didn't work. I'll try it again when I get home though and let you know hat happens. Thanks.
     
  6. Smijo

    Thread Starter New Member

    Nov 15, 2012
    26
    0
    I used the circuit given in the previous post and ran a simulation on LTspice, with a pulse of 0.35V for 200us to simulate the output of the IR detector, and the output is not what is expected. I simulated the 555 before with a 5V source to see what I expect when the timer is on. I set the pulse to 5V for 200us, and again, the output is not what is expected for when the timer is off.

    edit: Even with a constant 0.35V and 5V, the output of the 555 is 0V.
     
    Last edited: Nov 18, 2012
  7. Smijo

    Thread Starter New Member

    Nov 15, 2012
    26
    0
    Upon further inspection, that circuit did work. Thanks!
     
  8. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Excellent! Glad to be of assistance.
     
Loading...