Light sensitive Switch

Discussion in 'The Projects Forum' started by RodneyB, Jan 30, 2014.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    I need some advice on How to reduce the sensitivity of the light sensitive switch shown in the attachment. Basically what is happening is the LED's are coming on way before they are needed.

    I use the 741IC
     
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi,
    A quick fix would be to change the fixed R3 resistor to a 10K potentiometer.
    E

    EDIT:
    You must also add a clamping diode across the relay coil, in order to protect the transistor
     
    Last edited: Jan 30, 2014
  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Great Thank you very much for the advice

    Regards

    Rod
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    1. How about the Vf and If of the LEDs?
    2. What does these LEDs used for ? (car,motorbike,bike,other)
    3. How is the I_relay?
    4. Maybe you can using bjt or mosfet to replace the relay?
    5. Are you trying to do a delay to turn on/off the LEDs?
     
    Last edited: Jan 30, 2014
  5. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    OK a couple of your questions I don't understand so just going to answer the ones I do.

    The light sensitive switch is used to switch many things thus the 10 Amp relay, its a waste for the LED's however it is a standard PCB so I just use it. There is a delay switching on and off basically I call it cloud delay.
     
  6. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    How about the Vf and If of the LEDs? (as 3V/20mA)

    A 10 Amp relay, it could be a reed relay.

    If you using the spec of LED is 3V/20mA, it better only using about 80% of 20mA that equal to 16mA, 16mA*4 =64mA, so you can using 2SC1384 to replacing the BC547, and take the relay away, just using 2SC1384 to drive the LEDs.

    But if you doing this way, it will affecting the LEDs driving ability and delay time.
     
    Last edited: Jan 30, 2014
  7. jjw

    Member

    Dec 24, 2013
    173
    31
    If R7 is for hysteresis, it should be connected to + input and should be much smaller, maybe about 100kohms.
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    a simple and cheap fix would be to put a piece of tape over the light sensor.
     
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