LDR/Dark sensing Lighting Circuit Controller Help

Discussion in 'Homework Help' started by dantheman2155, Feb 19, 2012.

  1. dantheman2155

    Thread Starter New Member

    Feb 19, 2012
    4
    0
    Hi,
    Attached is a lighting controller circuit. If possible could someone tell me how it operates/functions? including which LED indicates below ambient lighting initiating the bulb etc.
     
  2. dantheman2155

    Thread Starter New Member

    Feb 19, 2012
    4
    0
    Attached is a lighting controller circuit which turns on the bulb when darkness is sensed by the LDR. If possible could someone tell me how the circuit and its components operates/functions? including which LED indicates below ambient lighting initiating the bulb etc. Please help! :) Thanks
     
  3. evilclem

    Member

    Dec 20, 2011
    118
    16
    For a start, the LDR does not sense darkness, it senses light.

    The op amps are operating as comparators. When the positive input is driven higher than the negative output, the op amp will turn on the output voltage.

    For the circuit to perform the required task some assumptions need to be made with regards to how it is drawn. First, R3 and LED RED are connected to the output of the first op amp. Second, the NAND gate input is the only other device connected to the output of the first op amp.

    When it gets darker, the resistance of the LDR increases. This drives the middle voltage of the potential divider up. As this voltage is driven up, it will eventually cross the voltage point set by the potentiometer on the op amps other input.

    Assuming the first op amp can sink enough current to turn on the green LED, then the green led indicates the sun is up.

    Assuming the base of the BC337 can sink enough current to turn on the red led, then the red led is turned on when the sun goes down. This in turn switches on the bulb.

    The thermistor works in the same way as the LDR on the first op amp but simply switches the second op amp on when the temperature of the bulb gets too hot.

    The idea of the NAND gates is to turn on the orange LED to indicate over temperature in the bulb but only if the bulb is on. I suspect that this final NAND gate is set to rapidly switch the orange LED on and off uncontrollably but I'll let you investigate this.
     
    dantheman2155 likes this.
  4. dantheman2155

    Thread Starter New Member

    Feb 19, 2012
    4
    0
    Cheers that is exactly how I perceived it worked. I meant light not darkness, just tried to portray that it turned the bulb on when the sun is down. Thanks!
     
  5. dantheman2155

    Thread Starter New Member

    Feb 19, 2012
    4
    0
    "When the positive input is driven higher than the negative output, the op amp will turn on the output voltage." You mean driven higher than the negative input right?
     
Loading...