PBP and 7 segments passive LCD

[fratello]

Here : http://memweb.newsguy.com/~rhuang/ I found one schematic of a clock using 7 segments passive LCD. Since this is one old obsession for me, to re-use the LCD's from different devices (like clocks, electronic calculator, etc), I wonder if it's possible to write in PBP the code for driving a such display. Any advice it's wellcome. Thanks in advance for every suggestion.

[Jerson]

Whatever you can do in ASM, you can do in PBP.

Just for the benefit of others, I am posting the link you refer to
http://memweb.newsguy.com/~rhuang/LCD/LCD.html

[Gusse]

Hi Fratello,

Passive 7-seg LCD is very similar to LED 7-seg. Additional step you have to include to code is to invert all LCD signals once in every 1-2ms. This way you generate needed AC waveform for the panel.

BR,
-Gusse-

[Darrel Taylor]

If you want to drive an LCD using a PIC, you should use a PIC with an LCD driver.

Depending on how many backplanes the LCD has, the waveform can get very complicated because you cannot leave a net DC potential on the crystals over time or it will destroy the LCD.

You can turn the segments on and off fairly easily by just toggling the pins, but it won't last very long and you'll soon have a very ugly looking display.

For instance, here's the waveform for an LCD with 4 backplanes using a real LCD driver.
Duplicating those signals with a 16F84 or other is nearly impossible.
4818

[fratello]

Thank You all for reply !
I not intend to do schematics verry complicated...I look at Huang schematic and I think it's possible to re-use many of passive LCD I have. The hardware it's ok for me; I wonder if I can use my code for termometer with 7 segm. - LED with this schematic; maybe it's possible to connect DS18B20 to pin 4 of 16F648 ? "Additional step you have to include to code is to invert all LCD signals once in every 1-2ms. This way you generate needed AC waveform for the panel." :confused:
I wrote code for termometer with LED display, common anode and common cathode. Which of them will be better ?

[Gusse]

Somehow Darrel's comment reminded me why I didn't continue with passive LCD displays. Most of the passive LCD specs says max 50mV DC, even some worked OK with higher DC levels for long times without any degradations.
This was a very good comment from Darrel. Thanks!

I never did try cap de-coupling, which could work to remove DC component. Don't know if this would work but give a try.
Try for example 1-10uF caps in series on every LCD signals. If it is not working, then try to increase value.

I'l try to check this with my old passive LCD and let you know if any success...

BR,
-Gusse-

[fratello]

Another example, this time using Atmega8. Great ! I will try this ...till writting my own code in PBP.
http://www.radiolocman.com/shem/schematics.html?di=63917