Lcd segment display

Discussion in 'The Projects Forum' started by mx tommy, Aug 29, 2006.

  1. mx tommy

    Thread Starter New Member

    Jul 17, 2006
    Hi all, I need to use a 7 segment LCD display (4 digit, 40 pin) on a PIC microcontroler project I'm working on, and I need some help...

    Here is the LCD... Digikey part# 67-1794-ND
    datasheet -

    Ok, so my question is, how do I use this? :| do I need some sort of driver IC?

    Thanks, Thomas
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    The segments are labled A-G, and DP, as follows:

    ..._a _
    f| _g_ | b
    e| _d_ | c o dp

    Notice the chart on the spec sheet that shows which pins go to which segments (there are four sets of segments, so they use 1A, 2A, etc. per the drawing). It appears this LCD runs from 5V AC (to the common pins), and you would provide half bias to the segment pins in order for them to light. By selectively lighting discrete segments you create numbers/letters, e.g. by lighting segments a,b,c,d,e,f (not lighting g) would give you the number "0" (lighting all segments, sans the DP, would give you the number "8").

    Rather than use an LCD, you may want to check on using the Lumex LED versions. The LED's are DC and either common-anode or common-cathode, so you either pull the segments low or drive them high (respectively) through a ballast resistor (with +5V, a 221 ohm would be fine).
  3. mx tommy

    Thread Starter New Member

    Jul 17, 2006
    Sorry, I should have been more clear, It needs to be easily readble in direct sunlight, so LED's are more or less out of the question. What I need to know, is what is "half bias"? That and are there any tricks to using the display with less then 40 pins, using some kind of Driver IC? if not, how does one create an AC signal with a microcontroller?

    Thanks again, Thomas
  4. n9352527

    AAC Fanatic!

    Oct 14, 2005
    There are LCD driver ICs available. The LCD needs to be biased with AC, or pulses, and not constant DC. It is actually a bit of a bother trying to use straight LCD.

    I suggest you look for LCD modules with internal drivers instead. They don't cost that much and come with parallel or serial interface and pretty easy to use.
  5. Søren

    Senior Member

    Sep 2, 2006

    Lots of tut's on the web, so saves me the time explaining :)

    Here's one driven from a PIC:

    And here is a PFD that's more informative on the general idea of driving (non-intelligent) LC Displays (LCD's), although it uses an Atmel µcontroller:"driving LCD display"