How to Adjust the Backlight on an LCD Alarm clock?

Thread Starter

TheDoctorDanko

Joined Jan 22, 2019
18
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.jpegF4D257F8-8389-437A-A15E-B0425794DBF8.jpeg935610A3-9D9E-4F1E-9FF3-5D84AE482744.jpeg4B7ACBBB-5C2A-4D02-B6E8-495518C20092.jpeg
 

wayneh

Joined Sep 9, 2010
17,153
Does the light only stay on while the button is held? You might try laying a piece of foil over those contacts.
 

Thread Starter

TheDoctorDanko

Joined Jan 22, 2019
18
Does the light only stay on while the button is held? You might try laying a piece of foil over those contacts.
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.
 

wayneh

Joined Sep 9, 2010
17,153
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.
 

Thread Starter

TheDoctorDanko

Joined Jan 22, 2019
18
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.
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.
 

wayneh

Joined Sep 9, 2010
17,153
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.
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.
 

djsfantasi

Joined Apr 11, 2010
7,763
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.
 

Thread Starter

TheDoctorDanko

Joined Jan 22, 2019
18
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.
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!
 

Thread Starter

TheDoctorDanko

Joined Jan 22, 2019
18
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.
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.
 

wayneh

Joined Sep 9, 2010
17,153
To be honest I’m not entirely sure. The adapter says AC View attachment 170074

but where the input is connected to on the circuit board says DC. View attachment 170075

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

Thread Starter

TheDoctorDanko

Joined Jan 22, 2019
18
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.
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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