Topic: LCD Dimming
There has been a lot of talk on this forum about dimming the LCD to intermediate backlight brightness levels, and the standard response has been that it's a hardware limitation: only full-on, dim or off are supported.
Is a hardware hack to get PWM-controlled 0%-100% LCD backlight brighness possible without too much trouble?
Looking at the r37 schematics, on page 3, I see that C523 (and R501) limits the rise/fall time of LCD_BRIGHT to about 2.2ms making PWM difficult (certainly at a high enough switching frequency to avoid flicker). Maybe this was done to avoid feedback loop instability in U501, the backlight inverter... I don't know, I haven't looked at the datasheets properly yet.
If you removed C523 and applied a PWM waveform to LCD_BRIGHT (pin A19 on the MX21) would you be able to dim the backlight or would the inverter go unstable? (Or some other problem I haven't thought of :-) Also could you increase(?) the resistance of R525 and R526 to decrease the dimmed LCD brightness (this would be minimum brightness available in the aforementioned possible PWM scheme)?
As for generating the PWM signal, easiest way would appear to be to use a spare GPIO on the cryptoprocessor (easiest to code that way), or use PWMO in the MX21 (pin H19, available at test point J107) and hack up some code in the kernel to control it.
Bunnie or others, any comments? Thanks!