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From: cgordon@vpnet.chi.il.us (Crash Gordon)
Newsgroups: sci.electronics
Subject: Re: Design a bar graph
Message-ID: <273510f4-521.3sci.electronics-1@vpnet.chi.il.us>
Date: 5 Nov 90 10:55:04 GMT
References: <16307@s.ms.uky.edu> <10546@milton.u.washington.edu>
Lines: 33


>Author: [Ken Tindle]
>I have three binary lines, for eight possible states (yeah, oh wow).  How
>can one light seven LED's from this, with zero having all LED's off and
>seven lighting all seven of them, in bar graph fashion?

Easy.  Use the smallest EPROM you can program. Apply your three binary
signals to three bits of the address bus.  (Preferably the three LSBs, but
it doesn't realy matter).  Now program the chip so that the data output
presents the desired LED pattern for each valid input.

>As a final touch, one should tax each digital
>line with but one standard TTL load. 

And so it does.


>Author: [Brian Totty]
> As a related question, are there any 4 bit -> 7-segment LED
> decoder/driver chips that represent the 4 bits in Hexadecimal
> rather than BCD with garbage for the top 6 values?

See above.  (Although this doesn't get you a driver, it does do the decode.)

This technique can do all kinds of weird translations and lookups.  In fact,
with a counter on the address input and PWM-type data, low-quality audio can
be reproduced.  Just run the data lines directly to an amplifier/speaker. 
You can store 8 phrases (well, words -- unless you've got BIG EPROMs :-), or
chain the data bits together for one longer phrase.  I've fit "Hello" on one
bit of a 27256 ...

----------------------------------------------------------------
Gordon S. Hlavenka                       cgordon@vpnet.chi.il.us
Disclaimer:        "EPROMs:  They're not just for code anymore!"