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PIC24H and LCD module

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waz2k5
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2008/11/16 22:50:41 (permalink)
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PIC24H and LCD module

Hello,

I have been a project that requires the use of an LCD module. Now I know there are 3.3V LCD modules out there, but it is very hard to come across them.

I would like to know if anyone knows the best ways to drive a 5V LCD module using a PIC24H series MCU.

Thanks.
#1

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    vikramgholap
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    RE: PIC24H and LCD module 2008/11/16 23:13:20 (permalink)
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    See, you can give 5V isolated power to the LCD still you can interface your LCD ( data lines and RS,RW,EN) with any 3.3V controller.
    5V is required only for LCDs internal operation. Logic need not be 5V level
    #2
    waz2k5
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    RE: PIC24H and LCD module 2008/11/17 07:12:49 (permalink)
    5 (1)
    Thank you. I thought that may be the case, just wanted confirmation.
    #3
    MBedder
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    RE: PIC24H and LCD module 2008/11/17 08:45:57 (permalink)
    5 (3)
    All character LCD modules based on HD44780 (and their clones) LCD controllers work perfectly at VDD from +2.7V to +5.5V (see HD44780 datasheet). The only issue is a Vlcd DC voltage which is measured relative to Vcc and must be in Vcc-3.5V to Vcc-5V range for normal temperature rated or in Vcc-5V to Vcc-8V range for extended temperature rated LCD modules.

    This means that with +5V Vcc the Vlcd can be obtained from the same +5V Vcc voltage by using a resistor voltage divider or a pot, while with +3.3V Vcc this requires a negative voltage source (from 3.3V-5.5v=-0.2V to 3.3V-5V=-1.7V). Such negative voltage can be obtained from various sources - existing system negative supply (if any), RS232 level converter (such as MAX3232, if any) V- pin, dedicated charge pump voltage inverter IC etc.

    But the most flexible way to obtain this negative Vlcd voltage is to implement a simplest charge pump rectifier using a dual Shottky diode (such as BAT54S or similar) and two ceramic 0.1 uF caps. An input to this rectifier is a PWM or square wave generated on a free PIC24 pin. In case of PWM it becomes possible to control the LCD contrast without a pot - just by changing a PWM duty cycle.

    I widely use this approach in many projects and never have any headache with 3V->5V level shifters or pullups on "5V tolerant" pins.


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    #4
    gip_mad
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    RE: PIC24H and LCD module 2008/11/18 02:29:40 (permalink)
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    Very nice!!! I'll try this method on my new project! Thank you MBedder!
    #5
    john bond
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    RE: PIC24H and LCD module 2008/11/18 05:43:42 (permalink)
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    grinA real neat solution Mbedder - Thanks

    Regards for Kwa Dukuza, deep in darkest Africa
    #6
    DarioG
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    RE: PIC24H and LCD module 2008/11/18 12:45:51 (permalink)
    3 (1)
    I missed this yesterday Smile

    Funny, I'm going to implement the same thing on a SED1520-based LCD these days.
    Had in mind the same thing, only with 1uF capacitors... maybe they don't have to be this large.

    GENOVA :D :D ! GODO
    #7
    ecuburner
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    RE: PIC24H and LCD module 2008/11/25 13:03:31 (permalink)
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    Is also possible using a graph display like GDM12864A that is a 128x64? For may opinion looking datasheet electricaly is the same of a charachter display.
    I wait your answers.
     
    Best regards.
    #8
    MBedder
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    RE: PIC24H and LCD module 2008/11/25 13:29:14 (permalink)
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    Due to the higher duty cycle value the graphic displays require higher (i.e. more negative) Vlcd voltage (-7..-20V typ). The KS0108 controller/driver Vdd is rated at +5V +-10% so it is not possible to use its direct connection to 3.3V logic/MCU.
    #9
    rmteo
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    RE: PIC24H and LCD module 2008/11/25 13:40:56 (permalink)
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    I use several different graphic LCD's with KS0108 controllers (128x64, 128x92) and T6963 (240x64, 240x128) with PIC24FJ at 3.3V and they work fine without level translation.  GLCD's are powered by 5VDC.


    #10
    MBedder
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    RE: PIC24H and LCD module 2008/11/26 05:36:04 (permalink)
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    Although this may work, the KS0108 datasheet says that VDD = 5V +-10%. So I woud have used this for hobby purposes only.
    post edited by MBedder - 2008/11/26 05:37:18
    #11
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