Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!gatech!ukma!tindle
From: tindle@ms.uky.edu (Ken Tindle)
Newsgroups: sci.electronics
Subject: Re: Design a bar graph
Message-ID: <16310@s.ms.uky.edu>
Date: 4 Nov 90 07:23:26 GMT
References: <1990Nov3.200047.11252@athena.mit.edu>
Reply-To: tindle@ms.uky.edu (Ken Tindle)
Distribution: na
Organization: U of Kentucky, Mathematical Sciences
Lines: 39

In article <1990Nov3.200047.11252@athena.mit.edu> chuck@mitlns.mit.edu writes:
>In article <16307@s.ms.uky.edu>, tindle@ms.uky.edu (Ken Tindle) writes...
>>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?  A dot display is
>>easy, but bar is tougher.  As a final touch, one should tax each digital
>>line with but one standard TTL load. 

Well, I've got four solutions to this now, here's one I didn't think of:

>   [suggests cascaded AND gates]
>      Takes three chips 1 74xx138 and 2 quad and gates. How many did
> it take you?

This is a good solution, wish I'd thought of it!

There are three other answers I see:

o EPROM
o PAL
o change to analog, use LM3914 driver

One can program either an EPROM or PAL, with PAL being a little less wasteful,
to give the right output pattern for any input pattern.  This'd certainly
work, but one must take care to watch dc current drive.

The analog driver approach and EPROM approach were the two I thought of.
The EPROM needed programming and buffering, and the analog was just.. kinda
messy.

Glad I posted, since the AND solution is probably the one I'll use, and I
didn't think of it at all.  Would use a PAL, but just don't have all the 
pieces needed here to make it work.  But now I have the incentive! 

--------------------------\ /-----------------------------------------------
INTERNET:tindle@ms.uky.edu | "Could you please continue the petty bickering?
BITNET: tindle@ukma.bitnet |  I find it most intriguing."   ---    Data, 
Ken Tindle - Lexington, KY |  Star Trek, The Next Generation, "Haven"
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