GP2X Backlight Force


paxl13

Member
Joined
Jul 16, 2006
Messages
279
Hi there,

I'm currently learning on how to code on 2x. and I was asking myself if
there was a way to dim the backlight.. to do some effect, and maybe
sove battery life.

Thank you
paxl13
 
paxl13 posted on Aug 3 2006 at 07:07 AM said:
Hi there,

I'm currently learning on how to code on 2x. and I was asking myself if
there was a way to dim the backlight.. to do some effect, and maybe
sove battery life.

Thank you
paxl13
I hope so, but I don't think there is.

The voltage is 17 volts and it comes from the DC-DC power regulator that runs the whole GP2X.

I don't know how you set voltage on the chip, normally it is resistor pairs, in which case a potentiometer or variable resistor could replace one of the legs and we would have a dimming knob.

I personally would expect the colors to improve and be less washed out, I would be much more interested in the picture quality improvement than any battery savings. (I believe there are 3,000mAh batteries out there somewhere, a test batch was given to craigix, the UK distributor)

Edit: that is only on the MK2 to clear up any confusion, on the MK1 the LEDs seem to be directly battery voltage dependant, you will notice them flicker as the load on the batteries changes.
 
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Yeah, on the MK2, the Power/Battery led are directly voltage dependent,
but it's an hassle since on mine with my 2600 mAH, the powerled dont open
and the battery led open rarely before lossing everything.

It would be better if the led code ajust himself to the max power of the Battery...

Do we have in SW the voltage of the battery or not ?

paxl13
 
paxl13 posted on Aug 3 2006 at 10:08 AM said:
Yeah, on the MK2, the Power/Battery led are directly voltage dependent,
but it's an hassle since on mine with my 2600 mAH, the powerled dont open
and the battery led open rarely before lossing everything.

It would be better if the led code ajust himself to the max power of the Battery...

Do we have in SW the voltage of the battery or not ?

paxl13
I meant the backlight for the screen, I don't know why you are talking about the power/battery light here.

We do have the software for seeing the voltage, I don't remember who was using it.

On every unit but my pre-order First Edition, the LEDs have been installed away from the face, so it is nearly impossible to see them in bright light.
 
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It should be pretty easy to isolate the voltage line to the LEDs and attach a potentiometer to it; but naturally this isn't an ideal solution, a software one would be. The backlight can be turned on/off in software apparently (music player) but as far as dimming it.. who knows.
 
If you turn it off and on with rapid succession (this is called PWM, pulse width modulation), it should look dimmer.
 
Epicenter posted on Aug 6 2006 at 11:50 AM said:
It should be pretty easy to isolate the voltage line to the LEDs and attach a potentiometer to it; but naturally this isn't an ideal solution, a software one would be. The backlight can be turned on/off in software apparently (music player) but as far as dimming it.. who knows.
That seems like a poor hack when it is connected to a configurable DC-DC convertor chip.

Blah posted on Aug 6 2006 at 12:04 PM said:
If you turn it off and on with rapid succession (this is called PWM, pulse width modulation), it should look dimmer.
Yes, the DC-DC convertor chip in the GP2X is making 17 volts now (for the backlight), and 3.3 volts (on EXT pins, and possibly processor) and 5 volts (that is being tapped for the USB "hackaday" hack) and maybe even more voltages.

They are set somehow, either software (Bios, modules, bootstrap), or hardware (resistor pairs).

I think that the pdf for the power chip said something about mhz PWM and it being adjustable. IE very clean PWM suitable for a processor PSU (obviously), the PWM is making the voltage, the width of the pulse determines the final voltage over time.

At millions of cycles per second I think the DC-DC chip is doing a fine job, lets just figure how to adjust it.
 
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