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From: tindle@ms.uky.edu (Ken Tindle)
Newsgroups: sci.electronics
Subject: Re: Design a bar graph
Message-ID: <16327@s.ms.uky.edu>
Date: 7 Nov 90 15:21:56 GMT
References: <16307@s.ms.uky.edu> <423@bartal.CRLABS.COM>
Reply-To: tindle@ms.uky.edu (Ken Tindle)
Organization: U of Kentucky, Mathematical Sciences
Lines: 23

In article <423@bartal.CRLABS.COM> phillip@bartal.CRLABS.COM (Phillip M. Vogel) writes:
>Use something like an NE590 (Signetics 3 to 8 demux), which is
>something like a 74138 with high current high voltage open
>collector outputs.  Put all the LEDs in series with a ~20 mA
>current source driving one end (the anode), and the cathodes
>tied to each output of the 590. The only catch is that your
>current source has to be able to put out a voltage of about 15 or
>so volts, depending on the LEDs you use.

OK, this is solution #5.  I received mail from Brian Rhodefer from Tek
suggesting the same thing, but he substituted a 7445, which might be a
bit more common.

I'm curious as to the implementation of the current source, though.  What
are some favorite current source circuits?

I think National has a chip in a TO-92 case that does something like this.

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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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