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'[PIC] Segmented LCD'
2012\01\30@085056 by Bob

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I'm working on a simple project, a 3 input temp readout with a 21/2 digit LCD output, for HVAC work.Pretty simple with 3 multiplexed 7 segment LED's. However I want to use the LCD so it can be battery powered. The data sheet says the LCD needs AC input. The more I read about this the more confused I become. Do I simply reverse the polarity to the LCD periodically? Can I use the same multiplexed setup as for the LED? I can't seem to find a definitive answer to this problem. It can't be all that complicated. Can it?                                                                                             Thanks                                                                                              Bob

2012\01\30@091241 by Matt Bennett

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On Mon, January 30, 2012 7:51 am, Bob wrote:
> I'm working on a simple project, a 3 input temp readout with a 21/2 digit
> LCD output, for HVAC work.Pretty simple with 3 multiplexed 7 segment
> LED's. However I want to use the LCD so it can be battery powered. The
> data sheet says the LCD needs AC input. The more I read about this the
> more confused I become. Do I simply reverse the polarity to the LCD
> periodically? Can I use the same multiplexed setup as for the LED? I can't
> seem to find a definitive answer to this problem. It can't be all that
> complicated. Can it?


LCDs are quite a bit different from LEDs, enough so that LCD drive
peripherals are getting built into microcontrollers:
<http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2091&param=en022834&redirects=lcd>

The PIC16F190x are some really low cost PICs with the LCD peripheral.



Matt Bennett
Just outside of Austin, TX
30.51,-97.91

The views I express are my own, not that of my employer, a large
multinational corporation that you are familiar with

2012\01\30@091548 by alan.b.pearce

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> I'm working on a simple project, a 3 input temp readout with a 21/2 digit LCD
> output, for HVAC work.Pretty simple with 3 multiplexed 7 segment LED's. However I
> want to use the LCD so it can be battery powered. The data sheet says the LCD needs
> AC input. The more I read about this the more confused I become. Do I simply reverse
> the polarity to the LCD periodically? Can I use the same multiplexed setup as for
> the LED? I can't seem to find a definitive answer to this problem. It can't be all
> that complicated. Can it?

Microchip make several micros for driving LCD segments directly, and handle all the AC drive requirements.

Check out the page at http://www.microchip.com/pagehandler/en-us/technology/lcd/ and click on the 'products' tab just above the picture.

I haven't checked, but suspect there will be some application notes as well, that would explain the principles.


-- Scanned by iCritical.

2012\01\30@101111 by Bob

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I have looked at these and thought they were for LCD modules. I will look at the data sheet more closely and try a couple samples.
                                                               Thanks
                                                               Bob
{Original Message removed}

2012\01\30@174856 by IVP

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> The data sheet says the LCD needs AC input

LCD segments do not like prolonged DC. In this timer

http://home.clear.net.nz/pages/joecolquitt/0sp505.html

the LCD driver provides the backplane, which is an AC frequency
that might be somewhere from 100-200Hz, which is internally common
to all segment drivers. Similar to strobing an LED display, but for a
different reason. Note that for the segments driven directly (DP, colon)
I've had to add a gate for each to multiplex the backplane output provided
with the off/on signal from the PIC

Before using the ICM7211 I used discrete latches and gates with a 555
for the backplane

Jo

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