Light Sensor circuit not sensitive enough in dark room

Discussion in 'The Projects Forum' started by paddyhughes086, Mar 1, 2016.

  1. paddyhughes086

    Thread Starter Active Member

    Jan 30, 2011

    I have a Light circuit that works perfectly out doors were there is a big change between Light and Dark.
    I have built a second circuit for indoors to turn on a LED lamp at night and go off in the day but the room just doesn't get bright enough in the day for the LDR to pick up the change and turn off the LED.

    I am just wondering if I change the potentiometer to a 100k would this help. Or should I change the 100R resistor

    Light Sensor.jpg

    Light Sensor.jpg
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    hi paddy,
    You could try increasing the value of the 100R to say 10K.
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Ldr are useless for sensitive light, better to use a photo diode like TEPT5700, BPW34,

    Ideally get an ohm metre ,and measure the resistance of the ldr in the darkroom in different places, that will give you an idea of its resistance increase, then you can make the pot value to suit.
    Last edited: Mar 1, 2016
  4. TheButtonThief

    Active Member

    Feb 26, 2011
    Have you thought about the feedback loop?

    Maybe the reason why the circuit isn't switching the light off when the sun rises, is because the room is lit by the light >.<
  5. twohats

    New Member

    Oct 28, 2015
    Similar answer to Eric's.
    Remove the 100R and fit a temporary potentiometer. Adjust to suit switch ON and switch OFF.
    Then fit a suitable fixed resistor.
  6. paddyhughes086

    Thread Starter Active Member

    Jan 30, 2011
    Sorry for the slow reply I was sick. Thanks everybody for the quick reply much appreciated .
    I will give it a go.

    Would the TEPT5700, BPW34, work in my circuit or would I need to build a new circuit

    Originally I did this this but I put the LDR on fly leads and removed it from my light source.

    Will give this a go