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Automatic Night Light with solar charger

Discussion in 'LEDs and Optoelectronics' started by Skorekaj, Mar 21, 2014.

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  1. Skorekaj


    Mar 21, 2014
    Hi All,

    Im a total noobe when it comes to this stuff but here we go.
    I got the idea to create a night light for my 2 children that would turn itself on at night and off when daylight is detected.
    So far so good, that all works fine with what i got. But i thought, wouldn’t it be awesome if we had a solar panel to charade the batteries up during the day?
    The solar panel charges the battery just fine, but only when i break the circuit to on the right hand side of the battery.

    So the question is, how can i break the circuit so that current doesn't flow around the circuit and just charge the battery ?

    I have the attached ciruit:

    1: LDR
    2: Variable resistor
    3: LED
    4: NPN transistor
    5: Battery, 3 x 1,2 v rechargeable batteries
    6: solar cell, producing some 22 mah at around 4 v

    Attached Files:

    • LDR.jpg
      File size:
      93 KB
  2. BobK


    Jan 5, 2010
    Hi and welcome to the forum.

    The way your circuit is working it will draw more current when "off" then when "on". This is because you are using the transistor to bypass the LED, and just connect the resistor to ground. You need to arrange the transistor switch so that it is on when dark and has the LED in series with it instead of parallel.

    You also want a diode between the solar panel and the battery so that battery will not back-feed the solar panel when it is dark.

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