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Bias Voltage for Multiplex LCD Question

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I have a multiplex LCD (datasheet attached) that I want to use with the PIC16F913 from Microchip.

I understand that multiplexing uses multiple commons, but how do I know how many bias voltage levels to use? I attached a section of the datasheet dealing with the LCD driver. They have a typeA and typeB waveform, but that just deals with the phase. They also have a 1/3 mux, 1/2 bias and a 1/3 mux, 1/3 bias to choose from.

The LCD datasheet has nothing about bias voltages - how do I choose which combination to use? Can I use either? Thanks!
 

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blueroomelectronics

Well-Known Member
I've used the 16F917 with a static LCD and it was fairly easy. Try breadboarding it first with the 3 10k resistors as shown in the datasheet. Search the forums here for Cricket and you can see my code & schematic.
 
I breadboarded it and coded it for 1/3mux with 1/3, then 1/2 bias (both type A waveform). When I set it up for 1/2 bias, the segments that aren't active show up faintly, but I can see them. That doesn't happen when I set it up with 1/3 bias.

Any idea why one would work better than the other?
 
On the VLCD pins in 1/2bias:

VLCD3: 5V
VLCD2: 2.5V
VLCD1: 2.5V

In 1/3bias:
VLCD3: 5V
VLCD2: 3.32V
VLCD1: 1.67V

I tried it with both type A and B waveforms, both have the same results of poor quality in 1/2 bias mode.
 
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