How to Adjust the Backlight on an LCD Alarm clock?

Discussion in 'The Projects Forum' started by TheDoctorDanko, Feb 12, 2019.

  1. TheDoctorDanko

    Thread Starter New Member

    Jan 22, 2019
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    Hello there! I am working on a small project of customizing an alarm clock. There is a function to turn on an orange backlight to see the time, but I was wondering if there was a way to keep this function on constantly. The Circuit Board/buttons appear to be contact switches and I’m just not positive on how to wire it in a way to keep the backlight on full time. Any thoughts? 5F9D9BD6-4291-422B-8751-7DEFDCFFF9BD.jpeg F4D257F8-8389-437A-A15E-B0425794DBF8.jpeg 935610A3-9D9E-4F1E-9FF3-5D84AE482744.jpeg 4B7ACBBB-5C2A-4D02-B6E8-495518C20092.jpeg
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Does the light only stay on while the button is held? You might try laying a piece of foil over those contacts.
     
  3. TheDoctorDanko

    Thread Starter New Member

    Jan 22, 2019
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    Thanks for the reply! And what happens is one press triggers the light to come on (approx 15 seconds). However if you press it again during that 15 seconds it shuts it off. Works like a momentary switch but with an auto shut off I guess.
     
  4. paulktreg

    AAC Fanatic!

    Jun 2, 2008
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    Probably not designed to stay on permanently?
     
  5. wayneh

    Expert

    Sep 9, 2010
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    If you don’t mind losing the functionality of the switch, it might not be hard to just power the light directly and bypass all the controls. If you can get inside without destroying it.
     
  6. TheDoctorDanko

    Thread Starter New Member

    Jan 22, 2019
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    That was my next thought as well since I’m not worried about turning the light on and off - just keeping it on when the clock gets power is what I need.
    But before I blew the LEDs I have I wanted to see if it were the right move. The clock has two forms of power I could potentially tap into - an AC adapter that puts out 6v and a 3v battery supply for when the power goes out.
     
  7. TheDoctorDanko

    Thread Starter New Member

    Jan 22, 2019
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    Yeah it’s definitely not designed for it but I do believe it’s possible. It’s just two simple LEDs that backlight it. Suppose I could always set up a separate battery for them just to keep it on.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    The 6V is fine. Is it DC or AC? You need just two things, a current-limiting resistor and a diode if the power supply is AC. LEDs are diodes but they can’t tolerate much reverse voltage and it would be wise to use a normal one for that duty.
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    What happens if you hold the button in?

    If the backlight stays on, then soldering a small piece of wire from the ring to the center of the button contacts of the PCB might do it for you.
     
  10. TheDoctorDanko

    Thread Starter New Member

    Jan 22, 2019
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    To be honest I’m not entirely sure. The adapter says AC 8D08D4F3-F624-420C-8610-6FCB04D228EE.jpeg

    but where the input is connected to on the circuit board says DC. 6F096D9B-3CDA-485C-BD91-BD5E8074C6A6.jpeg

    I do have a couple of resistors laying around though that would be an excellent idea!
     
  11. TheDoctorDanko

    Thread Starter New Member

    Jan 22, 2019
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    This was my first thought and I gave it a go but unfortunately no dice. It turned on as if the button was pressed but then it still managed to shut off automatically.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    That’s a DC adapter, so you can easily poach some power from there. Just a resistor, at most one for each LED if they’re in parallel. One resistor for both if they’re in series. It’s possible the resistor(s) is already in place if you can identify it. Otherwise start with 470 ohms and reduce that if it’s too dim.
     
  13. TheDoctorDanko

    Thread Starter New Member

    Jan 22, 2019
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    That’s genius! Seems simple enough. Pretty new at this so thank you for all your help! I’ll see what I can do!
     
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