GP32 Backlight Fading?

[fishybawb]

Is there any way to control the backlight brightness? I'm looking to get a sort of "fade out" effect with the LCD's light, like some mobile phones do when you don't press any buttons for a while. Anyone know if it's even possible?

Thanks

 

[Vimacs]

it is, but i dont know nymore wich register it is.
blinking the backlight realy fast should giv the same effect through, check the wiki for the right gpio.

 

[Squidge]

It's possible to do a bad fadein/out, but not a nice one, as the lcd doesn't seem to be linear, so it kinda gets half way and then switches off

 

[SolidSnake]

it is, but i dont know nymore wich register it is.
blinking the backlight realy fast should giv the same effect through, check the wiki for the right gpio.

​

ufs, blinking is bad for the lcd life, isnt it?

 

[ninjak]

Could Most likely do it using some Pulse Width Modulation into the back light register. I have no idea whether flashing the back light is good or not. But you would be able to accoomplish the fade by slowly decreasing the duty cycle. That will give you a nice linear fade. Same thing is done to slow CPU fans down. under 7 V or something, they just shut off, so you don't get a nice adjustment of speed.

 

[wyefye]

you guys are aware that the backlight is not a cold cathode, but multiple leds? led's are fully dimable - this is why the "flickering the screen" makes absolute and utterly no sense to do. I'm positive the led's can be controlled via software - Just like a Palm.

-----
-no, blinking the lcd is not bad.
-no, flicking the backlight will not destroy it.

-Q: "It's possible to do a bad fadein/out, but not a nice one, as the lcd doesn't seem to be linear, so it kinda gets half way and then switches off"
A: Wtf?

-Q: "Is there any way to control the backlight brightness? I'm looking to get a sort of "fade out" effect with the LCD's light, like some mobile phones do when you don't press any buttons for a while. Anyone know if it's even possible?"
A: Absolutely.

Best person to ask would be craigix.
----


This is what i dont understand about everyone complaing about the backlight sucking so much power -THIER LED'S! you can run a white one one a AA for days. the only thing that could be eating so much battery time is the cpu's running at fullspeed constantly.

 

[Vimacs]

its either on or off, nothing in betwene...
and toggeling it realy fast is like reducing the power.

 

[wyefye]

could you please provide a quote, or schematic, or some sore of documentation?

Unless the controller is setup for either on/off operation only, dimming is entirely possible. If diming is not possible due to hardware restrictions, just add some hardware - ie: potentimeter. Dimming the lcd btw has nothing to do with the lcd panel itself, but the light - the LED's, which are fully dimable.

Btw, toggleing it is in no way "like" reduceing power.

 

[Zap]

could you please provide a quote, or schematic, or some sore of documentation?

Unless the controller is setup for either on/off operation only, dimming is entirely possible. If diming is not possible due to hardware restrictions, just add some hardware - ie: potentimeter. Dimming the lcd btw has nothing to do with the lcd panel itself, but the light - the LED's, which are fully dimable.

Btw, toggleing it is in no way "like" reduceing power.

​

Someone here obviously never studied any physics..

PWM (pulse width modulation) doesn't really reduce the power,
but it does indeed reduce the energy on the output.
The power is transmitted only intermittently, thus lowering the energy.
And if the leds, or whatever light source it is, gets less energy
they dont shine as bright.

Edit : I'd also like to add that your computer power supply does exactly
the same internally to reduce the voltage from the power transformer, then
the output is smoothed by a capacitor.. But that's in no way mandatory.

Also, I don't know what kind of lighting the GP2X uses, but if it is LEDs it
should be fine as most LED displays are multiplexed and flicker to save
energy.

 

[wyefye]

took physics, extremely boring subject.

Forgot im talking to smart people, or in the case of some, think thier smart.


I've never heard of PWM, i get the jist of it though. were talking extremely fast switching here right, cause if it was something like 50-60 hz, its going to suck so bad i wouldnt want it. and even still, if it was faster, i think ill still opt for hardware dimming, such as installing a potentimeter. Unless the firmware gets Alot better and can actually control the devices its running on.

Also, the cap in the PSU is mandatory - if it wasnt there to smooth the power, your drives and everthing else that needs power would be fuxed. kinda like running a vacuum cleaner next to your television.

edit: sp.

 

[Zap]

When I was saying not mandatory, it wasn't in the PSU example, it was in general.

Also, I've often ran my vacuum cleaner next to my TV and none of them ever exploded..
The only problem I've had maybe is the fact that the vacuum cleaner is louder than the TV.
You know, very smart people are paid to do a very cool thing named « Electromagnetical
compatibility », which allows you to use more than one device at time..

Also, frequency isn't an issue here as we are dealing with PWM, which is pulse width
modulation. You only change the duty % of the output, not its frequency. You can modulate
at high frequencies, if the hardware allows it, and notice no flickering. Of course modulating
at 50 Hz would be an idiotic idea.

Also, I'm looking forward to hearing how you're gonna make a potentiometer automatically
dim the light after x minutes of inactivity. I think that might deserve a Nobel prize.

 

[Zap]

*Double post, delete this..*

 

[wyefye]

Older televisions accepted the electomagentic interference.

things still freak when power isint smoothed, especially complex electronic devices - its needed in most cases.

Dimming the backlight after x amount of time would be a stupid idea because if you leave the gp2x idle that long, your obviously not playing it - and wasting battery time. Also, since it will obviously be monitoring button activity, what happens when your playing some lame RPG that makes you go thru some stupid crazy long cutscene that you have to pay attention to or you miss vital info- only to have the screen go dark? (i know its a run-on sentence.)

If you dont like the brightness with a potentimeter installed, just adjust it. something like the volume control on a cheap walkman.

Also zap, i did not mean to offend you - if i did.


"Also, I'm looking forward to hearing how you're gonna make a potentiometer automatically
dim the light after x minutes of inactivity. I think that might deserve a Nobel prize."


Step one: install hardware potentimeter.
Step two: Dim backlight to desired level after x amount of time.
Step three: Go stair surfing and land on head so amnesia sets in.
Step Four: Goto step three.

nobel prize please?

 

[nubie]

"Also at I'm looking forward to hearing how you're gonna make a potentiometer automatically
dim the light after x minutes of inactivity. I think that might deserve a Nobel prize."


Step one: install hardware potentimeter.
Step two: Dim backlight to desired level after x amount of time.
Step three: Go stair surfing and land on head so amnesia sets in.
Step Four: Goto step three.

nobel prize please?

​

:lol: :lol: :lol: :lol: :lol:

You didn't do anything
I think PWM will work just fine for dimming, it is how many household dimmers work.

I am a student taking automotive technology courses and PWM is an important part of our curriculum.

PWM works perfectly for dimming, I don't think they are planning to use dimming to save battery power (your monitor doesn't dim out, it just shuts off for power saving).

I think they want cut-scenes that dim out well. I guess not though, but pwm will still dim quite well.

The Cellphone charger for your car works quite well, and it is just a PWM Integrated Circuit.

 

[Squidge]

The LCD backlight uses up ~50mA, which is a lot for battery powered equipment running off 2xAA.

If you reduce the brightness by slapping a 50% PWM on it, you will obviously reduce the brightness, and reduce the current consumption. However, there's no way to PWM it in the 2X, so all you can do is control it directly - which means you have to flip a GPIO pin to turn it on/off manually under interrupt. This method has been tested and works, but looks ugly as just over half way, the light switches off completely.

Please be our guest and report back if you wish to try a hardware mod though.

 

[Zap]

Also zap, i did not mean to offend you - if i did.

​

No, actually you quite amused me.

And about the potentiometer idea, why not if its for fine tuning the light.
But I doubt its in fact possible with the hardware.. With the old FLU units
you could easily hack one on the wires, but now that's its included on the
original PCB design it would include cutting tracks and soldering on them, and
there's probably not enough room for this as the case is pretty compact.

 

[wyefye]

I love you guys.

 

[BradN]

So what's the verdict on the backlight type? LED or CCFL? LED should be perfectly dimmable via PWM (but if the PWM update rate is too low, it will flicker). CCFL will probably do as described above and drop out totally below some duty cycle.

I actually made a PWM control module in verilog as a component of our final project (10 LED 1 dimensional pong game with 2 digit score per player) in an FPGA lab in college... works pretty slick on LEDs, but then again we used a 2 mhz update rate (which was way, way overkill). Used the PWM to make the "paddles" fade out after you press them, and make the score fade into the new value when it changes.

There's actually a couple output schemes that pwm refers to, the simple way has a timed on/off signal like:

|`````````|___

Another way can be obtained by continually adding a duty cycle to a register and outputting 1 whenever the addition carrys, which would look a bit like (the big difference is we assume that one ` or _ is the maximum resolution with which the signal can be outputted, so here it's updated continually to best match the desired duty cycle, where the previous way obtains the right average much more slowly):

|```|_|```|_|```|_

for the same duty cycle. The second way allows more resolution without getting choppy by avoiding the need of long on/off times to get the right ratio, but the first way requires less hardware interaction if it's to be done via interrupt trigger or whatever.

EDIT: this was actually kinda a bad example, since it uses 9 timeslices of on, and 3 timeslices of off, but if the ratio weren't as even, the differences would be more apparent (think fraction simplification).

 

[fishybawb]

Well this has been lovely and all, but I was after a software control method. Also, if you'd all stop arguing and read the title of the forum, you'd notice I posted this in the GP32 section, so I'm not asking about the GP2X

So has anyone got any examples of how I might get this effect in code?

 

[Zap]

Well this has been lovely and all, but I was after a software control method. Also, if you'd all stop arguing and read the title of the forum, you'd notice I posted this in the GP32 section, so I'm not asking about the GP2X

So has anyone got any examples of how I might get this effect in code?

​

It's not really different, the concept is the same.. But is there a way to control
the backlight only with software on BLUs ?