The Cranky Sysadmin A world of technology, fun, and ignorant rants.

December 17, 2011

A nifty homebrew LC meter

Filed under: Electronics — Cranky Sysadmin @ 8:57 pm

I spent the day putting together a less unattractive LC meter then the one I had on a breadboard. As I said in the last post, the design is from Kerry D Wong. As an exercise, I made an attempt at getting the parts strictly from the local radio shack.

Instead of a raw ATMega328P chip, I used an Arduino Uno and an arduino protoboard. The inductor was the only piece which I had a hard time sourcing from Radio Shack. I used a 100uh ceramic inductor ripped from an old Radio Shack CB, so maybe that counts. If you feel like winding your own, you can use one of the many air core inductance calculators on the net. It says a 222uh inductor is about 79 turns on a 1.5 inch diameter with some 32 awg magnet wire (comes out to about 0.9 inches. the wire is available from Radio Shack of course). Interestingly, I built an inductor and measured it with my new meter. The inductance was about 263 instead of the expected 222.

When you start interfacing your circuit with the arduino, the cal button goes to pin 12 on the header. The rest of the circuit from Kerry Wong should be easy enough to follow. If you have to use different values for the inductor or the 1000pf (1nf) cap, be sure to edit the sketch and change the constants for those parts. You’ll also want to remove all include headers except the LCD header and the Freq counter header. I’ll post a version that works with the arduino and the serial LCD interface from Parallax. There aren’t too many changes.

I had a hard time calibrating the inductance side. The following steps seem to work:

  1. Plug in the meter to power and set it to capacitance testing.
  2. Let the meter warm up for about 5 minutes. Temperature seems to have an impact on the oscillator.
  3. In capacitance mode, hit the calibrate button.
  4. switch to inductance and measure a known inductor.

How accurate is the meter? I tested about 50 parts, and given the tolerances, I’d say the meter is well within 10% accuracy on both capacitors and inductors. I have no proof, but it feels somewhat less accurate on inductors. Below are some pictures from the process. Do you notice something that I forgot? Yes, I forgot to include a power switch.

The bottom of the protoboard after completion of the circuit.

The cover of the project box with parts installed.

Measuring inductance.

Measuring Capacitance

1 Comment »

  1. […] finally cleaned up the source code from my rendition of the LC Meter. Here s the source. Here is a modified freq counter library which works with my Arduino Mega2560. […]

    Pingback by LC Meter Update and Source « The Cranky Sysadmin — January 23, 2012 @ 6:50 pm

RSS feed for comments on this post. TrackBack URL

Leave a comment

Powered by WordPress