Swtiching Scheme; light intensity based switching (PHOTOSWITCH)

Discussion in 'The Projects Forum' started by Jbfaheem, Mar 9, 2016.

  1. Jbfaheem

    Thread Starter New Member

    Mar 8, 2016
    I want a switching scheme.
    I want to switch between two circuits based on light intensity sensing. I want my circuit to sense light input from sun (i am working on solar panels) and switch between two circuits according to radiance levels. So, what i basically need is "light intensity based switching".
    My Requirements are:
    Switching time should be very less to ensure power regulation.
    Components employed should be economical and easily available.
    Possible Solutions:
    Solutions that i thought are:
    Use of
    1. photo switch
    2. phototransistors and relays.

    I want to ask if there any adjustable photswitch available that switches on our required values of irradiance?
    Do any One have any circuit diagrams employing phototransistors to switch between 2 circuits?

    All suggestions are welcomed.
  2. ian field

    AAC Fanatic!

    Oct 27, 2012
    You need a Schmitt trigger so the switching is clean and not flickering back and forth.

    LDRs are getting hard to come by because the cadmium sulphide is too toxic for RoHS.

    Sunlight contains enough IR that you can get away with a bog standard photo diode like they used to use in TV front panel remote sensors - all the modern ones are integrated with amplifier and 38kHz filter.

    Most solar garden lights directly sense from the solar panel whether to light up or not - reverse engineering a few of those could give some answers, but recent ones have that function integrated into a custom chip.
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Comments on sensors:
    Light dependent resistor, LDR, showed little change in resistance with large changes in angle to sun.
    Might be better if used with a filter.
    Best results were with a single cell solar cell giving .56 V in full sun & @ .36 V when loaded with a .39 ohm R gave detectable V changes with small angle changes.
    ' would use a comparator, relay driver, & SPDT relay. NC to charge battery NO on at high sun to other load.
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Further to post #2, can you use your solar panel output current and/or voltage as the signal to control the switching?
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Using the main SP for measuring V,or I, is unreliable because of variable loading on SP.
  6. ian field

    AAC Fanatic!

    Oct 27, 2012
    Not a filter - just attach a bit of tube so only perpendicular light can strike the sensor.