Re: [lcd4linux] GPO circuitry

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

Hi Aragon,

> However, I'm having difficulty figuring out how your idea will work with the
> resistors?

Every resistor can be switched on and off with a transistor, and every 
resistor allows a specific current. If you choose the resistors in a way 
like a "binary system", so that the current will be 10, 20 and 40 mA, 
you can control the current from 0 to 90 mA in steps of 10 mA.


> Instead of using pin 17 for a 1 bit operation, I'm going to use it to strobe
> a pair of CD4514s.  Each CD4514 can take 4-bits of binary input, so I'm
> going have one connected to bits 0-3 of the parallel port's i/o lines, and
> the other connected to bits 4-7.

This is very similar to the GPIO schematic on the web page, except that 
we use a 74HCT573 as a latch.

> So what will this achieve?  Well, it will give you 32 switchable channels
> that can be controlled from software.  You could have 16 of these providing
> 16 levels of backlight brightness, and another 16 performing other switching
> operations (panel LEDs, relays, etc. etc.).  It really adds a huge level of
> flexibility.  You could hook up a relay to cut your PCs power if you so
> wanted!

I'm not shure, but what I've read is that the CD4514 is a demultiplexer. 
This means that it has 16 outputs, but only one can be active at a time! 
Are you shure that this is what you want?

bye, Michael

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