Cascading LM3914's

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Stephen Robinson Contact options for registered users 's Avatar (by Gravatar) posted on
May 3, 2005, 11:25 am
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Hi Guys,
I am building a circuit that measures vacuum and displays it on a LED
bargraph and was wondering if anybody has any experience with the LM3914 led
driver IC, specifically, building displays with multiples of 10 led's.
I have the data sheet and have built a 30 led display in dot mode, but I may
need to go to either 40 or 50 led display to improve resolution but  cannot
find any info on what is needed so it could be scaled correctly.
The data sheet has a lineararity circuit, which I thought would be
satisfactory for using as  span adjustment, but in hind sight, am not so
sure. This is designed to be set and left. I want something that can be
adjusted as needed.
I hope I have given you enough info for you to help.
Stephen



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Adrian Jansen Contact options for registered users 's Avatar (by Gravatar) posted on
May 3, 2005, 9:56 pm
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Re: Cascading LM3914's


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I doubt the internal accuracy of the comparators in the LM3914 is good
enough to do more than about 30 steps with any reliability.  You might
be better to use an A/D converter and digital display, like eg the
ICL7216 or similar.  You can get good digital panel meters from Lascar
Electronics.

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Regards,

Adrian Jansen           adrianjansen at internode dot on dot net
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Stephen Robinson Contact options for registered users 's Avatar (by Gravatar) posted on
May 4, 2005, 10:59 am
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Ok..Thanks. I will have a look at that. 30 leds MIGHT be enough. WIll try it
and take it from there.

Stephen






Geoff C Contact options for registered users 's Avatar (by Gravatar) posted on
May 3, 2005, 11:07 pm
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Stephen, you did not say if you want to make more than one or if you are
doing the project for fun, but a cheap $10 digital multimeter is a good
cheap way to incorporate into test or calibration equipment. It already has
a reasonable A/D and display, and is really cheap.

Stephen Robinson Contact options for registered users 's Avatar (by Gravatar) posted on
May 4, 2005, 11:06 am
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I'm making it for me and for fun, but will probably offer my results to a
couple of mates who want to build one as well.
I thought about using a digital display but I need 2 displays to compare two
vacuums and I suspect the display would not update fast enough. I use
multimeters in my job. Thanks for the input.

Stephen



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