After a lot of hustle and online search, I understood that an LCD segment cannot be driven like the LED ones and that I need a special driver. The problem is I cannot find a driver that I can understand how to wire and multiplex, does it make a difference if the LCD I am using have a backplane for each separate digit or 1 backplane for all 8? Can I use CD4543B driver to multiplex all 8? How to use multiplexing with a microcontroller that has LCD driver built in? Thanks
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\$\begingroup\$ You can't multiplex LCD displays like you can with LEDs. The 7 segment types generally have one common backplane terminal and a connection for each segment, and you have to drive each segment individually. \$\endgroup\$– FinbarrCommented Feb 16, 2021 at 21:32
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\$\begingroup\$ in this case I need to drive 64 different segments, do you know how can I do that? \$\endgroup\$– Seif_1999Commented Feb 16, 2021 at 21:56
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\$\begingroup\$ You could one 4543 per digit. \$\endgroup\$– FinbarrCommented Feb 16, 2021 at 22:00
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\$\begingroup\$ ok sounds good, what should I connect to blanking, phase and latch pins, and where to connect the backplane? I am sorry to bother you with so many questions, thanks \$\endgroup\$– Seif_1999Commented Feb 16, 2021 at 22:06
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\$\begingroup\$ this may help electronics.stackexchange.com/questions/524988/… \$\endgroup\$– jsotolaCommented Feb 16, 2021 at 23:50
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1 Answer
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An 8-digit LCD will (probably) not be a static drive type because it would require 60+ conductors.
Multiplexing (such as triplexing) reduces the number of conductors but the drive waveforms become multi-level and the contrast becomes more sensitive to temperature. You must have a display designed for the type of multiplexing you want to do.
There are chips designed for driving (say) triplexed multi-digit displays such as the MAX723x series. They tend to be expensive.
There are also inexpensive 8-bit micros with on-chip LCD drivers with various capabilities, which I would definitely recommend (you can do a search in your favorite families of products for the presence of such a peripheral and compare capabilities to your requirements).
There are other more Rube Goldberg methods of accomplishing this, but the above would be what I would suggest.
For example, this 8-digit display features 3 commons (triplexed), so it has only 30 pins for 8 digits. It has pins so it's aimed at relatively low volume/high price applications most likely. Note that the segment/common pairings are probably not what you'd choose- they are more dictated by the requirements of making the display conductors not cross over.
answered Feb 16, 2021 at 22:04
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\$\begingroup\$ thank you but if use an 8-bit micro with on-chip LCD drivers, I still dont know how to drive it for example AVR atmega329 has 4x25 LCD driverbut i need to drive 64, I hope I am miss understanding something here so you can correct me. \$\endgroup\$ Commented Feb 16, 2021 at 22:12
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\$\begingroup\$ Read the datasheet and reference manual and application notes for the microcontroller. Generally it will consist of setting up the peripheral, connecting it correctly to the display and anything else required and writing a '1' or '0' in some on-chip bits where you want the segment to be in one state or the other. Those bits will probably be scrambled. \$\endgroup\$ Commented Feb 16, 2021 at 22:15
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\$\begingroup\$ If you have 4x25 LCD driver it can probably be configured as 3 x 25 or 4 x 25 depending on your display. It should be adequate for an 8-digit (7-segment) triplexed or quadplexed display if it is compatible with bias and voltage specifications. \$\endgroup\$ Commented Feb 16, 2021 at 22:17