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9961Re: [cosmacelf] Re: Seven Segment Displays

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  • Lee Hart
    Apr 6, 2012
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      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

      > 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…- 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
      -- Mahatma Gandhi
      Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net
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