| Author |
Topic |
|
|
mmp
31 Posts |
 Posted - 30 Jul 2003 : 08:37:41
|
Hello,
I am using a different inverter than the one provided by ADS (the LS 520A) and I would like to be able to vary the brightness of the backlight. The inverter that I am using is ERG E2077C. The main difference between the two inverters is that the one provided by ADS controls the brightness by means of ramping (change of level in the voltage) while the inverter that I am using requires a pulse width modulated (PWM) signal. I noticed that in the sample application for controlling the brightness, ADS uses a function called "SIOBacklightPwm" to control the brightness which I thought it is doing it by PWM (since it's got 'pwm' in the name) but when I hooked up an oscilloscope to see what was really going on, I noticed that voltage ramping (voltage going up an down) was taking place. Indeed, the description says that it simulates a potentiometer to vary the level of the voltage in order to control the brightness of the backlight (which is consistent w/ how the ADS provided inverter works.) However, as I said earlier, I need a PWM signal to control the brightness. Are there any functions available that do that? In the sample application there is another function called "SetSA1111PWM0" and its description is "Set PWM level for backlight (SA1111 PWM0) " but no matter what values I try as its argument, nothing happens. My processor is SA1110; I am wondering if that has to do with anything. And if yes, is there a function that controls the PWM of an SA1110 instead of SA1111 ? Assuming that I am approaching this problem from a wrong angle, what would be the solution to obtain (out of the main board) a PWM signal that I would be able to vary (by software) ?
Thanks,
Marius
p.s., I am using GC+, SA1110.
|
|
|
mmp
31 Posts |
Posted - 30 Jul 2003 : 14:04:30
|
Follow-up: Analyzing the problem a little bit more, I found out that (just as the documentation says) there is a filter that converts the PWM signal so that it can be used with the ADS provided inverter (for voltage ramping.) Therefore, I will remove the filter to attempt to get a straight PWM signal and then try varying the brightness by means of the SIOBacklightPwm function.
|
 |
|
|
akidder
1519 Posts |
Posted - 30 Jul 2003 : 14:35:04
|
Hi Marius:
On the rev B GC Plus, the backlight PWM filter cap is C27 on the underside of the board near the backlight header, J13. On revs D and F, the filter cap is C142 on the top side, right behind J13.
You can remove the filter cap yourself, but do note that we can't warranty the board once you've reworked it. Good luck! |
|
|
|
mmp
31 Posts |
Posted - 30 Jul 2003 : 16:05:41
|
Hi Drew,
Thanks for the reply. The capacitor has been removed and I can control the backlight intensity by means of PWM using the SIOBacklightPwm function. The frequency is constant (approx. 7.4Khz) and I get around 8 levels of intensity (so, of course, it is not as smooth as it was when ramping was used.) |
|
|
| |
Topic |
|
|
|
All Forums
Hardware
Brightness by PWM
Forum Locked
Send Topic to a Friend
Printer Friendly