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9962RE: [cosmacelf] Re: Seven Segment Displays

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  • bill rowe
    Apr 6, 2012
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      driving a raw lcd is a bit of a bugger. I did it to prove to myself that i could but it didn't seem very practical. I was using a multiplex display which makes it a lot tougher though. The voltages and timing needed are all well within the 1802's capabilities so it's not a bad project idea. If you're interested, these posts and the links can give you voltages and timing ideas if you need them.http://hackaday.com/2011/02/10/driving-a-salvaged-lcd/http://arduino.cc/forum/index.php/topic,51464.0.html a good general LCD reference: http://ww1.microchip.com/downloads/en/AppNotes/00658a.pdf (it is somewhat PIC oriented but it's more general than that).
      > To: cosmacelf@yahoogroups.com
      > From: leeahart@...
      > Date: Fri, 6 Apr 2012 10:39:39 -0500
      > Subject: Re: [cosmacelf] Re: Seven Segment Displays
      >
      > On 4/5/2012 9:07 AM, aa3nm wrote:
      > > use a dead stupid LCD and wiggle the wires in simple
      > > hardware to get the contrast for the bits. In my case I was not
      > > going to go for a hex display but rather use the segments to
      > > represent the binary data bits...
      >
      > This should be easy for a simple binary display. There are a few
      > non-multiplexed LCDs on the market with all the segments brought out to
      > an actual pin. They look like an IC chip, but are glass instead of
      > plastic. They are typically found in bottom-of-the-line multimeters.
      >
      > These non-multiplexed LCDs have high contrast and wide viewing angle so
      > they often don't need a backlight. Power consumption is often very low,
      > down in the microamps region. They are pretty easy to drive. You need to
      > apply an AC signal (5v square wave is OK) between the segment and the
      > common backplane. It could be as simple as an exclusive-OR gate for
      > every pin. There are 1-digit BCD-to-7seg LCD drivers like the 4543,
      > though I don't know of any that display hex, however.
      >
      > There are a couple multi-digit hex-to-7seg LCD driver chips; the ICM7211
      > (not the A version) will drive four 7-segment LCDs, and displays hex
      > (0-9,A-F). The drawback is that the *input* is multiplexed. It's
      > intended to be driven by from a micro's output port with software, so it
      > will take a fair amount of hardware to make it work as a front panel
      > display.
      >
      > > My idea was to use segments E& C for a pair of data bits on each of
      > > 4 digits (thus 8 bits are displayed) representing either a 1 or be
      > > blank. Then I realized that I'd left a-whole-nother 8 bits unused...
      > > Why not use the upper set of segments (F& B) in a similar way for
      > > address display (good enough for a quarter K). This differed only
      > > slightly from a concept Lee had considered´┐Ż- that of using an 8 digit
      > > display and forming the bit number (1 - 7) to represent a 1.
      >
      > That would certainly work. I considered a binary display, but decided it
      > would be confusing (which pixel is which bit?). LCDs are sold by the
      > square inch, pretty much regardless of how many segments are in it. So I
      > figured it would be better to tie all the segments together to form the
      > actual numbers. It didn't change the hardware at all, but only required
      > an 8-digit display for 8 bits. I think my schematic for such a display
      > is still posted in the files section.
      >
      > --
      > First they ignore you; then they mock you; then they fight you; then you
      > win.
      > -- Mahatma Gandhi
      > --
      > Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net
      >
      >
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