controll 634 backlight brightness by hardware


New member
i'm thinking about buying a 634 serial display, because i'm not all that much a hero with a soldering iron. I would however like to be able to control the brightness of the backlight with a button on my case. Is it possible to simply vary the +5v needed for the backlight (only lower offcourse, i don't want to fry it) or is this impossible with this kind of display. In that case i would need a paralel one....

thanks in advance!
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CF Tech

Basically you would need to reduce the voltage supplied to +5v(LED) pin of J2 of the display.

Are you looking to vary it or just have "dim" and full settings?
USB LCD Displays - Graphic and Character LCDs with a Keypad


New member
wel, basically what i'd like to do is being able to vary it through my fan controller...this controller gives a voltage between 7 and 12 v, so i thought if i could reduce the 12v to 5 v, it should work...because when i then reduce the 12v (by turning down the fancontroller), the output would then be lower then 5 v, which would cause the backlight to dim...or am i talking complete nonsense?


New member
i don't really know if it's linear or pwm, but it's this one:*107038/action*2563
(this sites in german).

i don't know if this is helpful, but i already succesfyully connected this device to the fancontroller:*100108/action*2563
i'll search for something in english, haven't got time for that now!

thanks for the help anyway!! if aal companys would be this helpfull to their customers, life would seem a litlle brighter ;-)

i found the way to put the site in english..... if it appears in german to you, you should click on english in the left column, where it says "sprache"
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CF Tech

I cannot tell from the pictures. E-mail them and see if they will tell you if it is "linear" or "PWM". If it is linear I can work out the resistor you would need to protect the backlight. If it is PWM it is not very likely that you would like the result, since most likely it would visibly flicker.


New member
I finally got an answer from HAMA:

Yes, the Fan controller works with PWM.

Pulse width modulation fan speed control module (PWM)
12V DC input
13W per fan speed control channel
Supply PWM output 50~100% duty per channel

4 channel outputs
Fit 3.5" bay
LED back light around the knobs
Adjustable fan speeds
The LED back light becomes brighter as the fan speed increases.
with blue LED back light
The controller is designed to be used with constant speed fans only

So it seems that it uses PWM.... but i'm not a 100 % sure they got it right, because on the back it says 17 w/channel. You said earlier that this would cause the backlight to flicker, but I connected a neon glow wire to it, which doesn't flicker (allthough this uses an inverter, maybe that's the reason). Could you please tell me what resistor to use? I would like to give it a try anyway...


CF Tech

Are you looking at a yellow backlight or white backlight?

Do you already have the module, or you going to buy it later?


New member
i'm planning on buying this module:
Front View Yellow LED Negative Backlit, (CFA634-YMC-KS):

I don't have it yet, but i plan on ordering next month or something like that...