Re: [lcd4linux] GPO circuitry

[Michael R. <re...@eu...>]

Hi Aragon,

> I've seen lcd4linux's GPO system and example on the page.  I'm trying to
> find the right circuitry that must work similarly to the example on the
> page, but provide analog output.  More specifically, I'd like to control
> backlight intensity using a GPO by converting 3 bits of the binary data to
> 8 voltage variations to the backlight LED.

First, I think this is a good idea.

I'm planning to include code for software-controlled backlight like for 
a circuit like this: http://www.jalcds.de/images/4x20backlight.gif

But there is no intensity, just switch on/off

If you want intensity, I'd try thw following:

use the diode 1N4148, the resistor 150 Ohm and the transistor BD135 
three times.

the 100 Ohm petentiometer should be replaced by a resistor, it's value 
should be different for all three transistors, and show some binary 
scheme (e.g. 100 - 220 - 470). The output of all three resistors would 
be connected together on Pin 16 of the LCD.

I know that there may be cleaner solutions....

bye, michael

-- 
Michael Reinelt                                   Tel: +43 676 3079941
Geisslergasse 4                                   Fax: +43 316  692343
A-8045 Graz, Austria                          e-mail: re...@eu...