Rockbox General > Rockbox General Discussion
Sansa e200 - wheel light fade in/out, also display fade in/out
DB1BMN:
Hello,
first of all I would like to pay tribute to all Rockbox developers as this is my first post in this forum and I (re-)discovered Rockbox a few weeks ago and installed it successfully on a Sansa e250 V1.
I would like also to see a dimming of the brightness of the scroll wheel (fading not necessary).
Why? Well, I dislike the cruel blue backlite of the wheel and wanted to substitute the LEDs by amber color type.
The problem is, that the LEDs are not driven by constant current, but there is only a resistor for each LED. In the V1 hardware theese are the resistors R201 to R204 for LED1 to LED4 respectively which are 47 Ohms each. In addition theese resistors are put on the opposite side of the PCB (in V2 hardware there are on the same side). So a simply exchange of the LEDs from blue to amber will make the new LEDs glow in red destroy them within a short time, because te Voltage along the LED is still fitted to blue. An additional increasing of the resistors is necessary!
Therefore I propose to implement an software PWM algorithm similar like the dimming of display backlite (I did not look at the source code if there it is done by sofware) for driving the wheel LEDs with optional maximum range limitation (e.g. for red, amber/orange, yellow, green, blue white...).
I hope you know what I mean. If you need the currents, voltages, duty cycles etc. let me know, I am more familar to the hot iron than to coding at the moment ;-)
Regards from Germany,
Mark
AlexP:
Dimming for the existing LEDs is one thing, but it is unlikely that this would make it into the main build purely for one (maybe two) people that change the LEDs, as it provides a nonsensical menu option for everyone.
casainho:
I made a Rockbox code just to test a PWM on that LED. Since I remember, there are 4 LED and with lower duty cycle on them, we start by seeing 4 spot lights, which is ugly!
Just the actual current to that LED make the light glow on over all wheel, less current (I mean using PWM as I did) do not make all wheel illuminated but instead the 4 points... which I guess no one will like it.
I don't have that code with me, I just deleted it. On that time I wrote a simple task for Rockbox kernel, that just turns on/off the LED, doing a kind of bit bang PWM. I guess is a very simple code for you guys get what you are looking for.
Maybe would be good idea if you take some pictures of it as post them here.
DB1BMN:
Hello casainho,
I am very interested on your code/hacking expirience.
Yes this may be true, if you decrease the effective current on the blue LEDs that the brightess will decrease more than linearly (as in fact the current of a diode is depicted by an exponential function), but in my case I need to decrease effective current resp. voltage above the diodes, since the the amber (datasheet: http://www.reichelt.de/?;ACTION=7;LA=6;OPEN=0;INDEX=0;FILENAME=X100%252Fla_t68b-ly_t68b.pdf;SID=27@6@GT4KwQARsAABLKBs9df9f7353d437894c654c0fc8b0570fb) have got a Uf of 2.4 Volts in contrast to blue LEDs with up to 4.5 V.
I will do some exact measurements and pictures this evening and publish them.
Regards, Mark
casainho:
--- Quote from: DB1BMN on December 16, 2009, 05:31:51 AM --- I am very interested on your code/hacking expirience.
--- End quote ---
Are you able to make that code?
I can't right now do it, but I can guide on if you need.
--- Quote from: DB1BMN on December 16, 2009, 05:31:51 AM ---I will do some exact measurements and pictures this evening and publish them.
--- End quote ---
It's always a pleasure to see hardware/firmware hacks ;-)
Do you already know the Lyre project? Where we want to make a good quality Open Hardware audio player and recorder.
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