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LED timer

Discussion in 'LEDs and Optoelectronics' started by selbyreb, Apr 12, 2013.

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  1. selbyreb

    selbyreb

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    Apr 12, 2013
    I have a problem with setting up a timer for LED bulbs. I have a small unit which includes 2 x LEDs powered by a 3 volt lithium battery. At the moment the LEDs are on constantly but I need them to be on only during night time. Is there a timer which will enable this? I don't have mains electricity available near this unit
     
  2. GreenGiant

    GreenGiant

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    6
    Feb 9, 2012
    you could do it with a timer but this would probably draw more power than the LED's use being on all the time.

    if you want them to come on only when its dark then you can get a light sensing transistor that is off when there is light present, this should eliminate most if not all of the drain on the battery when its light out, and only turn on when its dark

    You will need to shield the transistor so that the LED's dont switch it off when they come on .
     
  3. selbyreb

    selbyreb

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    Apr 12, 2013
    Thanks for that Greengiant, just need to know how to integrate it into my item
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Yes, this can be done with a couple of low-Vgs MOSFETs and a few resistors, using an LDR (light dependent resistor) to detect ambient light level.

    I'll draw up a diagram for you, but I can't be sure how to "integrate it into your item" unless I know exactly what your "item" contains. Can you post the following information.

    1. Photograph(s) of the "small unit" showing the cell(s), the LEDs, and everything in between.

    2. Part number for the cell(s)

    3. Any markings on the LEDs

    4. Are any other devices connected in the circuit apart from the cell(s) and the LEDs? If so please describe them, including any markings on them.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    1,271
    Nov 28, 2011
    I've got a schematic drawn up. I just need answers to those questions.
     
  6. selbyreb

    selbyreb

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    Apr 12, 2013
    Hi KrisBlueNZ , thanks for the reply. Unfortunately I am awaiting delivery of the LED flashing unit. All I know at the moment is that the unit is powered by a button cell battery , CR 2032. It appears that the unit is enclosed in some kind of tape so whether I will be able to tell you what components are in the circuit remains to be seen. Once I receive the item I will be in contact with you again. Once again many thanks for your help
     
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