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Driving LCD 7-seg passive displays with PIC

I have a passive LCD with 8 7-seg digits plus point and some other
symbol. It has 23 connections.
I wish to drive it with a PIC that has LCD module built-in but I have
seen that all PICs capable to drive LCD have only 4 commons. I
supposed that was needed 1 common for each digit but probably I have
to use bias plus multiplex. In this case how can I do? I have not
found any application notes and info on internet. Thanks.
I wish to use a 16F917 PIC.
 
L

linnix

Jan 1, 1970
0
I have a passive LCD with 8 7-seg digits plus point and some other
symbol. It has 23 connections.
I wish to drive it with a PIC that has LCD module built-in but I have
seen that all PICs capable to drive LCD have only 4 commons. I
supposed that was needed 1 common for each digit

Not really necessary.
but probably I have
to use bias plus multiplex. In this case how can I do? I have not
found any application notes and info on internet. Thanks.
I wish to use a 16F917 PIC.

You have to double check it for sure, but 8 digits would need 64
segments. 23 pins (19x4) can drive 76 segments. So, it should be
possible.
 
S

Spehro Pefhany

Jan 1, 1970
0
I have a passive LCD with 8 7-seg digits plus point and some other
symbol. It has 23 connections.

What does the data sheet for the LCD show? Definitely multiplexed,
probably by 3 or maybe 4. You need that information.
I wish to drive it with a PIC that has LCD module built-in but I have
seen that all PICs capable to drive LCD have only 4 commons.

That's fine.
I
supposed that was needed 1 common for each digit but probably I have
Nope.

to use bias plus multiplex. In this case how can I do? I have not
found any application notes and info on internet. Thanks.
I wish to use a 16F917 PIC.


Best regards,
Spehro Pefhany
 
What does the data sheet for the LCD show? Definitely multiplexed,
probably by 3 or maybe 4. You need that information.


That's fine.


Best regards,
Spehro Pefhany

Can you explain me how the multiplexing with biasing works? I cannot
understand how to connect the wires and why there are different levels
of voltage in common pins rather than only 3 (-V, 0, +V).
 
L

linnix

Jan 1, 1970
0
I cannot understand how to connect the wires

There are four common lines from the uC to four common lines to the
LCD. It is definitely a one-to-one mapping.
 
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