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Old 7th May 2006, 08:45 AM   #1
DolbyR is offline DolbyR  Finland
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Default Looking for a LED voltmeter circuit

I'm currently building a 4 fan speedcontroller for my drive bay...it will be encased in an old cd drive casing.
I want to add speed display for all fans and i thought the easiest way to do this would be to build separate voltmeters for each fan. I'd like a circuit that i can either use a 2 segment led display or a circuit that will just run a regular 10-led bargraph...in case of the bar graph the first led should be able to light at 5v and the last one at 12...does anyone know any good circuits that will work. I did find some ICL 7106/7107 based circuits but they're designed for 4 segment led displays.
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Old 7th May 2006, 08:59 AM   #2
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LM3914 from national semiconductor..
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Old 7th May 2006, 09:10 AM   #3
DolbyR is offline DolbyR  Finland
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I think that's the same i used for a tachometer once, i just wasn't remembering which IC it was I was thinking if it wouldn't work with some resistances in front of each led to control the voltage they get?
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Old 8th May 2006, 03:35 AM   #4
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Nope...LEd are controlled by a current source inside the IC.current can be controlled extrenally by a single resistor.Output current programmable from 2 mA to 30 mA.
Study the application note before making conclutions....
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Old 8th May 2006, 06:45 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
the bar or dot graph display chip is easy to implement.
Try looking at http://www.electronics-tutorials.com/devices/lm3914.htm

BTW, Ian Purdie's (VK2TIP) site is full of good tutorials.
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Old 8th May 2006, 07:53 PM   #6
DolbyR is offline DolbyR  Finland
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I might try this one, and if i cant use it for what i need, i'll always find it some other use DIGITAL VOLTMETER
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Old 9th May 2006, 06:48 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
you're not listening!
You asked for a bar graph and yet keep referring to a numeric output even though two posters have told you what chip to use.
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Old 9th May 2006, 06:54 AM   #8
DolbyR is offline DolbyR  Finland
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I asked for a numeric led display circuit OR a bargraph circuit...sorry if it pisses u off that i dont want to use the IC ur offering me
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Old 9th May 2006, 07:14 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
that explains why your looking at 7106/7. I had not recognised two segment LED as being a numeric display.

The data sheet for the 7106/7 should give you all the details to set it up as a DVM.
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Old 9th May 2006, 07:31 AM   #10
DolbyR is offline DolbyR  Finland
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i guess i mixed the terms a bit anyway...what i meant is 2 numeric leds (i guess they're called 7 segment or something) anyway, i guess i'll try that circuit i posted the link to but leve one of the leds out, so i'll have 3 leds to show "00.0" i'll post some experiences after its done in this case the bay will have only one display
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