LCDs... how do I use them?

[Szech]

I saw these LCDs for $7, and I was wondering how they work.
http://www.allelectronics.com/online-store/scstore/p-LCD-53.html

Basically, I'm getting into circuitry, and am interested in things as such.

[tonym]

Hi szech,

These displays work by exciting a liquid crystal in a controlled electric field. Where a field is present, the LCD becomes opaque (dark)...where there is no field, the LCD is transparent (transmissive). There are small channels etched into the glass surface that define a 5x7 matrix of dots, 16 characters in length and 2 lines wide. This means that there are 5x7x16x2=1120 dots on the display, and the circuitry on the module is basically a decoder and multiplexer to write data to the individual 5x7 segments and a state register to tell the uP controller what state it it in (via the bidirectional data bus).

So in operation, you will apply two voltages -- the logic voltage (+5Vdc) for the on-module logic circuitry and a "contrast" voltage, for this module from 0 to 13.5Vdc to obviously adjust the darkness of the liquid crystal when it is excited (like on a Palm Pilot!). This module also has an option to be backlit -- it contains an optional LED for this purpose or it can be used in a transmissive mode (ambient room or sunlight passing through from back to front) or an electroluminescent (EL) mode (with an external EL panel behind the display -- like the Palm Pilot!!).

Generally these displays are used in digital multimeters (DMMs), point of sale devices (like credit card readers) and in gase pumps (for status info).

There's a simple application circuit shown on page 5 of the data sheet. It shows the LCD module interfaced to a Z80 processor. You could modify this to interface to any processor so long as you observe the timing and addressing criteria. I bet you could interface this to a Microchip PIC-type processor no sweat! You'd also need a ROM/RAM to act as a look-up table for the font code information for the module, or you could use a software implementation if you wanted to save on hardware.

Give it a shot and report back your progress!!!


Tony

[voogru]

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[Szech]

Thanks tonym! I have a couple of projects in mind, and if they go through, I'll post them up here!

[randy48]

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