[Entry] 4049 inductance meter

[Entry] 4049 inductance meter

Postby NiHaoMike » Wed Oct 03, 2012 10:39 pm

All the decent multimeters nowadays seem to have a built in capacitance meter, but only a few of the really expensive ones have a built in inductance meter. Dedicated inductance (LCR) meters, of course, are also really expensive.

The solution, of course, is to build an inductance adapter for any multimeter.
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It works by generating a stream of pulses and feeding them into a LR network. (The duty cycle must be very low to allow the inductor to "reset".) Two extra inverters operate as a comparator and a RC filter converts the output to a voltage that can be read by a multimeter. A series inductor ensures that even small inductances would generate pulse widths wide enough for the circuit to work, and an offset voltage used to zero the meter.

Then I realized that rather than an adapter, what I really wanted is a standalone inductance meter. Harbor Freight recently gave out a few coupons for free multimeters (with a $10 or so minimum purchase), so I ended up getting a few of those after buying some tools. Since I have several good multimeters for actual use, it made sense to convert one of those into a standalone inductance meter.
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http://i46.tinypic.com/2a0niwm.jpg
http://i48.tinypic.com/10p3myo.png
Complicating the design was the odd rail splitting, so I had to build a DC/DC converter to supply the circuit. I also made some optimizations to keep the current draw low in order to get acceptable battery life. It turns out that even that cheap meter has an input filter, hence the lack of it in the circuit. Finally, I cut a trace to to remove the decimal point and glued the dial in place.
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Re: [Entry] 4049 inductance meter

Postby ian » Fri Oct 12, 2012 8:46 am

Nice work, thanks for entering. Learning the basic of how to do something like C measurement is really illuminating!
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Re: [Entry] 4049 inductance meter

Postby NiHaoMike » Fri Oct 12, 2012 7:27 pm

ian wrote:Nice work, thanks for entering. Learning the basic of how to do something like C measurement is really illuminating!

It actually measures L, but I'm sure it won't take much to modify the design to measure C. (Although capacitance measurement is of questionable use since many good multimeters have it and ESR is a better measurement of whether a capacitor is still good.)
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Re: [Entry] 4049 inductance meter

Postby ian » Sat Oct 13, 2012 3:04 am

Sorry, slip of the brain, L indeed :)
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Re: [Entry] 4049 inductance meter

Postby systemstech » Sat Oct 13, 2012 11:36 am

Schematic in Eagle 6.3.0

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sch by systems tech, on Flickr

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brd by systems tech, on Flickr
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Inductance adapter.zip
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Re: [Entry] 4049 inductance meter

Postby systemstech » Sun Oct 14, 2012 8:37 am

Schematic in Eagle 6.3.0

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Meter Mod sch by systems tech, on Flickr

Board.

Image
Meter Mod brd by systems tech, on Flickr

Original.

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10p3myo by systems tech, on Flickr
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meter mod.zip
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Re: [Entry] 4049 inductance meter

Postby systemstech » Sun Oct 14, 2012 11:04 am

did some changes.

Image
Meter Mod sch v1a by systems tech, on Flickr

Image
Meter Mod brd v1a by systems tech, on Flickr

Haven't added the v- rail, changed connector size. If anyone can see a problem pls let me know or correct it pls.
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meter mod v1a.zip
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Re: [Entry] 4049 inductance meter

Postby astock » Thu Sep 26, 2013 3:48 pm

What is the range of this meter? Can I measure very small inductance, between 0.5uH and 2uH?

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Re: [Entry] 4049 inductance meter

Postby Retrovert » Sat Mar 15, 2014 1:11 am

Nice project and clever (ab)use of logic gates. Thanks for sharing the details.

I've seen a few interesting minimal L meters using an LM311 op-amp and the venerable 555. (Is there anything one can't do with a op-amp or a 555?) The discussion of how these things work was new to me, and I thought it might be useful to others trying to understand how the circuit works.

I tried to include two of them, but I can't post URLs yet. I'll edit this after I get approved. Sigh.
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