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MSP430F427 Low LCD contrast in 3,4-MUX Mode

Danut Stanciu
Prodigy 20 points
Other Parts Discussed in Thread: MSP430F427

Hi.

I have a problem: I tried to command an 4MUX mode LCD display with MSP430F427 but when I configured 3 or 4 MUX mode I have low contrast in LCD; when I tried with 2 MUX mode I got a good contrast (of course with missing segments). I visualized with an oscilloscope COM's segments and everything seem to be OK. If somebody knew about this problem please help me. Thank you in advance.

  • 0
    Guru 227245 points

    In the MUX modes, the COM lines dance a 'jitterbug' to make active segments appear but inactive segments to not appear while still keeping an effective AC voltage signal on the active segments. This results in decreased AC voltage on the segments. In 4x mode, the resulting signal is smaller than in 2x mode (and much smaller than in 1x mode), so the contrast is reduced.
    IIRC, you can adjust the voltage levels externally. Or, if you don't use the external voltage divider/generator part, increasing the general MSPs VCC might help (of course not more than 3.6V)

    The driver logic is explained in the users guide.

  • 0 in reply to Jens-Michael Gross
    Prodigy 20 points

    Jens-Michael, thank you for response.

    After more digging in documentation I realized that I need an processor with LCD_A controller which can adjust LCD voltage and bias (my processor has only LCD controller).

  • 0 in reply to Danut Stanciu
    Guru 227245 points

    On LCD module, you only have a basic contrast control with the external resistors on Rx3, especially the one between R03 and GND. I think connecting R03 to GND gives highest contrast. And rising VCC is another option.

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