Pwm Fade Example In Archive/backlight Fader


would be too good to be true. I don't quite trust it... but if it does work, that would be amazing news... finally we could adjust the backlight brightness! Yeah, no burning eyes anymore o_O

EDIT: The website of the guy who claims to have made this looks legit though. If I was to release some bricking virus, I wouldn't want to make a website like that... I wonder if I should try this.
 
Gonna try this right now, wish me luck!

Edit: It seems to work, but the screen is getting really flickery that way.
I wonder if thats a side effect of it, if it is we could probably forget about dimming the screen without an hardware mod.
 
does it flicker in the process of dimming or also afterwards when the screen is adjusted?
 
I bet the problem is that the process doesn't get scheduled often enough to smoothly dim the display - if the scheduling timer runs at 100hz (which used to be the standard and is kinda likely on here), then at best, the program can switch the backlight at 50hz (first timer tick on, next off) - and this is only if you want exactly 50% brightness... if other percentages are desired, the flickering would get worse since there must be times when the backlight is on or off for 2 or more cycles in a row to attain the percentage.

A "fully compatable" fix would be writing a kernel module to use a 2nd timer (if there is one) to give a higher interrupt rate, and then this can be used as a way to switch the backlight faster. It would come at a slight cost in system performance, since every interrupt will by nature do a little cache trashing and use up a little processing time, but it probably wouldn't be too noticeable.

A hack could be increasing the scheduling timer rate, but context switches are a lot more expensive processing wise than just handling an interrupt, so this probably isn't desirable.

An application specific, but easier to implement way would be using the 940 as a backlight switcher - if the program doesn't use it at all, it could run constantly switching the light, but probably this would cause a lot more power usage from the 940 than is saved on the backlight. Again, if a 2nd timer can be activated and routed to the 940, this could be an efficient solution, but otherwise it would be best reserved for demos and "special effects".
 
BradN posted on Aug 10 2006 at 02:33 AM said:
An application specific, but easier to implement way would be using the 940 as a backlight switcher - if the program doesn't use it at all, it could run constantly switching the light, but probably this would cause a lot more power usage from the 940 than is saved on the backlight. Again, if a 2nd timer can be activated and routed to the 940, this could be an efficient solution, but otherwise it would be best reserved for demos and "special effects".

I considered this but I doubt the LEDs use much power anyway-- if it were a big light stick like that used in LCD monitors and laptop displays it might consume a lot of power, but these LEDs shouldn't. I'd mostly want to dim it to reduce color washout, not that it's very bad anyway. I would like to reduce backlight brightness and increase it to simulate a burst of light in an explosion effect in my engine though ...
 
Last edited by a moderator:
Epicenter posted on Aug 10 2006 at 06:46 AM said:
BradN posted on Aug 10 2006 at 02:33 AM said:
An application specific, but easier to implement way would be using the 940 as a backlight switcher - if the program doesn't use it at all, it could run constantly switching the light, but probably this would cause a lot more power usage from the 940 than is saved on the backlight. Again, if a 2nd timer can be activated and routed to the 940, this could be an efficient solution, but otherwise it would be best reserved for demos and "special effects".

I considered this but I doubt the LEDs use much power anyway-- if it were a big light stick like that used in LCD monitors and laptop displays it might consume a lot of power, but these LEDs shouldn't. I'd mostly want to dim it to reduce color washout, not that it's very bad anyway. I would like to reduce backlight brightness and increase it to simulate a burst of light in an explosion effect in my engine though ...
So, if I take this right, you seem to think that this just activates the "turn off backlight" command. Just like when in the MP3 player, but at a high speed to dim it.

Nuts, I was hoping it was controlling the DC-DC chip through software somehow. Hardware mod still needed I guess.
 
Last edited by a moderator:
nubie posted on Aug 10 2006 at 10:15 AM said:
Nuts, I was hoping it was controlling the DC-DC chip through software somehow. Hardware mod still needed I guess.
No, the code is just strobing a bit in one of the MMSP2 registers (GPIOH). It's a mystery how the author figured out that bit 0x04 of that register controls the backlight, but apparently it does (I looked at the code but did not try to compile or run the demo).
 
Last edited by a moderator:
I didn't imagine a simple source would be put on the first page. Like it was said, it's absolutely not an exploit, the program just pulse-modulates the bit 2 in Register "H" and controls the brightness.
Unfortunately, when the backlight is switched on too shortly, it doesn't event light up, if you run the program you'll see it will go dimmer and just drop to black to some point.
I don't think we can bypass that with a simple PWM.

And you can trust the .gpe ;)
 
furrtek posted on Aug 10 2006 at 11:32 AM said:
I didn't imagine a simple source would be put on the first page.
I didn't put it up on the front page, I just reported it as news :).
 
Last edited by a moderator:
Epicenter posted on Aug 10 2006 at 03:46 AM said:
I considered this but I doubt the LEDs use much power anyway-- if it were a big light stick like that used in LCD monitors and laptop displays it might consume a lot of power, but these LEDs shouldn't. I'd mostly want to dim it to reduce color washout, not that it's very bad anyway. I would like to reduce backlight brightness and increase it to simulate a burst of light in an explosion effect in my engine though ...

It's not LEDs, it's a CCFL. Dunno how those work when you lower the voltage but based on the function of this program, lowering the voltage will turn it off rather than dimming it.
 
Last edited by a moderator:
Ranma13 posted on Aug 13 2006 at 02:56 AM said:
Epicenter posted on Aug 10 2006 at 03:46 AM said:
I considered this but I doubt the LEDs use much power anyway-- if it were a big light stick like that used in LCD monitors and laptop displays it might consume a lot of power, but these LEDs shouldn't. I'd mostly want to dim it to reduce color washout, not that it's very bad anyway. I would like to reduce backlight brightness and increase it to simulate a burst of light in an explosion effect in my engine though ...

It's not LEDs, it's a CCFL. Dunno how those work when you lower the voltage but based on the function of this program, lowering the voltage will turn it off rather than dimming it.

If that's the case (may be, I haven't opened the LCD assembly), the power consumption would be pretty high, yes. Usually CCFLs step up the voltage massively, I believe potentially to the thousands of volts (AC?) to drive the tube. If you alter the input voltage though you should be able to cause a linear change in the resultant voltage operating the tube, and a brightness change. But there are quite a few factors involved, really..
 
Last edited by a moderator:
Back
Top