Inductor question 2

[R.Spinks]

I would like to build a circuit which uses a variable inductor as the input
to set some states for output out of a micro. I was figuring I'd use an A/D
channel on a cheap micro and output based on the input (the inductor). But I
don't really know how to set up the inductor for this purpose. If the
inductor is tuned one way, I'd like the A/D to get X counts and as you tune
the other way you'd pass through a couple states and end up with the full
range rail voltage at the other end (so like 5v would be 1 state 2.5v
another and 0v another). I think I could do this with resistor networks, but
I want to use an inductor for what I'd like to build. Can anyone suggest a
relatively cheap circuit which can use the inductor as the input. I can
input a square wave to the inductor with a 555.. though.. I'm not sure if
that would work. Since a DC voltage would just be just a short -- I'm not
sure how to set up the inductor as the input.

 

[CFoley1064]

Subject: Inductor question 2
From: "R.Spinks" rspinks1@wowway.com
Date: 9/20/2004 10:13 PM Central Daylight Time
Message-id: <Ca2dndLC5talB9LcRVn-sA@wideopenwest.com

I would like to build a circuit which uses a variable inductor as the input
to set some states for output out of a micro. I was figuring I'd use an A/D
channel on a cheap micro and output based on the input (the inductor). But I
don't really know how to set up the inductor for this purpose. If the
inductor is tuned one way, I'd like the A/D to get X counts and as you tune
the other way you'd pass through a couple states and end up with the full
range rail voltage at the other end (so like 5v would be 1 state 2.5v
another and 0v another). I think I could do this with resistor networks, but
I want to use an inductor for what I'd like to build. Can anyone suggest a
relatively cheap circuit which can use the inductor as the input. I can
input a square wave to the inductor with a 555.. though.. I'm not sure if
that would work. Since a DC voltage would just be just a short -- I'm not
sure how to set up the inductor as the input.

If you use an air core inductor with a movable iron slug, you will get a
variable inductor. If the value of inductance is between 0.5uH and 50uH, you
can use a circuit like this to find the inductance (view in fixed font or M$
Notepad):

Q and D Inductance Tester
.---.
3K9 | |
___ _V_ | |\ ___
.--|___|--|___|-o----|H>O-|___|--.
| 2K 10 turn |/ 330R |
| | |
| |\ | |\ ___ |
o------|H>O-----o----|H>O-|___|- o
| |/ | |/ 330R |
--- | | Output
--- 1000pF | |\ ___ | |\ |\ ___ 10mV/uH
| '----|H>O-|___|- o-|H>O--|H>O-|___|-o---o
| |/ 330R | |/ |/ 39K | +
=== | ---
GND o ---
| |0.33uF
C| |
Lx C| | -
C| o---o
| |
o |
| |
=== ===
GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

The circuit, which is a mod of an ARRL circuit published a few years back, is
described at:

http://users.cableaz.com/~cappels/dproj/Lmeter/lmet.htm

You can place an op amp at the output of this circuit to amplify to full scale
output as desired. If your inductance is higher, you can play with the R and C
values to get a wider range.

Good luck
Chris