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Subject: RE: Backlight on recorder dimming?
From: Matthew P. OReilly (moreilly_at_moreilly.com)
Date: 2003-01-06


Hey all,

I had a similar revelation when I had my problems with the short in the
Archos... I noticed that there were two discreet backlight luminosities. I
haven't received my JB back from Archos tech support (where, oh where, has
my little Archos gone!) so I can't substantiate that it's supposed to or
not. I noticed a definite difference when I pressed "up" (towards the face)
on the DC power in jack, and I *think* the display got brighter when I
plugged it in. [The problem I had was a physical short somewhere in the
power circuitry which prevented the device from operating properly unless
the DC power was plugged in AND a physical pressure was put on the device to
alleviate the short or whatever it was.]

I had originally thought that perhaps the display had two settings - one for
low-power, one for higher-power (similar to many other devices) that gave a
brighter LCD output when an external power source was applied. On further
reflection, I'm not so sure, but that may very well be the case. (i.e.,
when the HDD spins up, the LCD drops into a lower-power mode to give more to
the HDD or what not.)

Does that sound consistent with anyone else's experience?

Matt

-----Original Message-----
From: owner-rockbox_at_cool.haxx.se [mailto:owner-rockbox_at_cool.haxx.se]On
Behalf Of Chris Muth
Sent: Tuesday, December 31, 2002 2:41 AM
To: rockbox_at_cool.haxx.se
Subject: Re:Backlight on recorder dimming?

Hey,

I too have noticed that the backlight will dim slightly when the disk spins
up.
I have also noticed that backlight will get slightly brighter when I apply
pressure to the
face plate. This is almost certainly a physical thing. Perhaps the light
spreader is getting
closer to the LED array and therefore the uneven propagation pattern ot the
light being emitted by
the diode is focused in such a way to provide more light? [Chris is just
thinking into the keyboard]
That is not a big deal and is beside the point.

Even when the disk is not spinning, spinning up, or spinning down, I can
press the
volume up/down (other buttons work but I will go with this example) button
and the
back light will come on and after 4s (the time I have it set for) it will
get slightly brighter,
and then get progressively dimmer and dimmer until the LEDs are off. Off to
the best my
feeble optic nerve can determine. I am willing to crack it open and stick
the backlight on the
oscope and see what truly is happening.

Being that this is a digital device, I am guessing that there will be many
discrete voltage levels going
into the backlight, and not random rail noise that would suggest that the
disk is putting noise on the
power rail.

Thank You for the responses.

Best Regards,
        Chris Muth <muthchris_at_muth.cc>

>Andreas Stemmer <Andreas.Stemmer_at_web.de> wrote:
>I had the same impression with my AJBR20: the backlight dims when the
>harddisc spins up because there's not enough power provided. If you want to
>program some dimming effects, you could use very fast on/off switching
>(pulse width modulation) which works quite well with any led like the
>backlight leds.
>
>Andreas Stemmer
>
>> >>I think the dimming is pretty cool, I just can't figure out why if
>appears
>> to get yellow and
>> >>I can't quite figure out what determines whether it dims or just goes
>off.



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