DIY do it yourself
Master classes, instructions, useful tips, recipes.
» » »The LED itself turns on in the dark
We need the following components:

one LTR-4206E phototransistor
one lithium CR2032 battery (3 V)
2N3904 transistor
1K resistor

Photos of these components:

Working process:
First, take the Transistor and resistor and solder them as shown in the figure:

Next, solder a phototransistor to this design:

Next, we attach the LED:

And then the power source:

And now we look at what we got:

This light will turn on when it gets dark

come back
Comments (13)
  1. serj
    #1 serj Guests February 9, 2011 11:56
    cool !! smile
  2. Dimonio
    #2 Dimonio Guests April 22, 2011 10:07
    Dear, you didn’t draw the diagram correctly. You are applying "+" power to the BASE !!!! (average conclusion according to the scheme) And in the pictures correctly (To the collector). Correct.
  3. Dimonio
    #3 Dimonio Guests April 22, 2011 10:08
    Firstly, the scheme will not work, and secondly, FT will bark as soon as it opens, because everything will go directly to it :))))
  4. yomko
    #4 yomko Guests March 17, 2012 16:42
    and just such a photoresistor?
  5. yomko
    #5 yomko Guests March 17, 2012 16:49
    Sorry, not a photoresistor, but a phototransistor? : feel:
  6. ilan
    #6 ilan Guests June 11, 2012 18:46
    and if there are 6 diodes at the same time, then what should change in this circuit?
  7. hrustal
    #7 hrustal Guests September 28, 2013 13:43
    Super! Thank you very much, this material is what is needed to implement my idea.
    I’m also looking for a solution for such an idea: I need an autonomous mini-backlight with a switch. Well here is a mini, as in your example with a photo-LED. Maybe you have such an operating time: an autonomous mini-backlight based on an LED with a switch (with position fixation). As an option, one could use a finger-type mini-flashlight, but I have not seen any with a switch that fixes its position))
  8. Lar_draco
    #8 Lar_draco Guests October 11, 2013 17:06
    my light was dim
  9. Dinar
    #9 Dinar Guests November 5, 2013 13:14
    But can I connect to 12 volts?
  10. Belek
    #10 Belek Guests November 20, 2013 13:16
    my light was dim
  11. Egor
    #11 Egor Guests November 20, 2013 15:48
    And in what way does it turn on in the dark?
  12. Alexander
    #12 Alexander Guests August 26, 2014 14:46
    You can find such a phototransistor in FIG. Can't you replace it with another?
  13. yurka
    #13 yurka Guests January 26, 2015 20:40
    will a phototransistor go out of the mouse? Or do you need a photo-LED?

Read also

Error codes for washing machines