LDR dimmer help

Discussion in 'General Electronics Chat' started by kakemann, Feb 18, 2013.

  1. kakemann

    Thread Starter New Member

    Feb 18, 2013
    2
    0
    I bought some headlights from a webstore for mounting on a rovio Ip camera robot. The headlights come with a ldr photoresistor which is light sensitive.
    They are supposed to dim down the light intensity when there is much light in the room. If the room is dark, the light should be at max intensity.

    However, the headlight I recieved is opposite. When I turn of lights in a room the headlights is dimmed down so they hardly give anyl light at all. When I turn on the lights the headlights light up at maximum intensity.

    I guess that something is not connected the right way, so I wonder if someone can give me some help. Will it help to cut off both of the connectors from the ldr to the circuit board, and switch the wires?

    [​IMG]

    [​IMG]

    [​IMG]

    Any other solutions?

    Help is appreciated :)
     
    Last edited: Feb 18, 2013
  2. MrChips

    Moderator

    Oct 2, 2009
    12,414
    3,353
    No. Reversing the LDR will make no difference.
    Did the dimmer come with instructions?
    Are there components or traces on the other side of the board?
    We will have to reverse engineer the circuit.
     
  3. kakemann

    Thread Starter New Member

    Feb 18, 2013
    2
    0
    Thank you for your answers.
    No. I tried to contact seller, but didn't receive answers.
    No. See picture under.
    [​IMG]
    What do you mean?

    Any other suggestions?
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,414
    3,353
    I need to see the connections and values of R4 and R5.
    Can you unsolder the wires at J2 and take a clear photo of the board?
    Also it would help if you posted the actual writing on R4 and R5.

    Was the board actually advertised to turn on the lights when the room is dark?
    Obviously the board is behaving in the opposite fashion.

    My educated guess is someone installed the wrong transistors on the board and the board was not tested.
     
    Last edited: Feb 18, 2013
  5. Elecman

    New Member

    Feb 19, 2013
    1
    0
    Photo resistors are light sensitive resistors whose resistance decreases as the intensity of light they are exposed to increases. The photo resistor material exhibits the same behavior independent of the circuit connections. Hence there is no polarity issue here with respect to the photo resistor. You can find detailed information from the below links.
    http://en.wikipedia.org/wiki/Photoresistor
    http://www.resistorguide.com/photoresistor/

    From your description, I think you bought a circuit designed for an opposite purpose. It is not clear from your picture to figure out how the circuit is set up and how the photo resistor, the load or the supply is connected. I can only see that there are three transistors cascaded to give some sort of gain control. Can you trace a schematic diagram of the circuit from your PCB layout? Then we can rearrange certain things towards your goal.:)
     
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