How Are You and Homebrewing Getting Along?
Build yourself an L/C Meter and minimise your Inductor and Capacior woes.
This article describes the construction of an L/C meter (Inductance/Capacitance meter). Its contents
should be of interest to the Homebrewer. I think it is an excellent school project where Radio and
Electronics are taught.
What do I want to share with you in this article?
1. The steps I take in embarking on homebrew projects.
2. Links to information on performing these steps.
3. Links to tutorials that are relevant to this project.
4. Any Do's and Don'ts that I think you should be aware of.
The use of links means that I do not have to provide lengthy explanations some of which might be under
Let me state here that the project is not of my design and any copyrighted material belongs to the
original author(s). My only involvement is in relating how I went about the construction of the meter
with the aid of information freely available on the Internet.
You are free to try to duplicate my efforts (at your own risk, of course) or, do your own thing. You may
even ignore part, or all, of this article for whatever reason.
Why write this article?
The Society members seem to be losing the art and joys of homebrewing. I look around today and see
(or is it hear?) less than a handful of Society members who may be involved in some form of
It is hoped that this article will provide some inspiration to the potential homebrewer and probably
re-ignite any waning interest in this rewarding aspect of the Ham Radio Hobby.
Additionally it may help to dispel from some people's mind, the notion that the Internet has taken away
some Hams' interest in Amateur Radio. What I have experienced is that the Internet has enhanced my
enjoyment of the hobby. It has provided me with a "gold mine" of information and has, to a great extent,
satisfied my quest for knowledge. It has given me the opportunity to see what other Hams around the
world are doing -- all this without having to resort to expensive magazine subscriptions or textbooks.
In relatively recent times the IRLP should also help to dispel this notion.
Why was this specific project chosen?
Well, it is my latest homebrew project. It works as expected and I think I understand well enough how it
functions to be able to assist anyone wishing to undertake this project.
Some background history
In the bad old days, finding the ballpark value of a capacitor or inductor involved the use of a standard
capacitor (100pF) and inductor (5uH), a GDO (Grid Dip Oscillator) and a look up chart provided in the
ARRL Handbook. If one did not have the ARRL graph, one had to manipulate the formula for resonant
frequency to calculate C or L. Electronic calculators were not easily available to the average local Ham
like me, and the slide rule was a nuisance. The accuracy of the measured results depended on the
accuracy and resolution of the GDO, which carried an analog dial. Today it is possible to build a GDO
with a digital readout in a housing with dimensions of say 4" x 6" x 3".
Today it is also possible to homebrew an L/C meter with a digital display that is accurate enough for the
My objective here is to show you how I did it.
In 1988/1989 a couple of construction articles appeared in a Ham Radio magazine for a DIY L/C meter.
The meter used an oscillator and a Commodore C64 computer running a BASIC program. Since I had a
C64 hanging around in good working condition I embarked on the project and had been using the meter
up until several months ago. This unit served me well. It had been invaluable in the construction of my
homebrew "3rd Method HF Transceiver".
There comes a time, however, when one needs to move on and so I decided some time ago to retire the
The L/C meter finds its place mainly in the hombrewing of rf equipment and is in fact of immense value
to anyone wishing to build his own receiver, transmitter or transceiver. If you are one of those who have
tried modifying a PC Switchmode PSU to run your HF transceiver, you know, (don't you?) that you
need a PI filter in the output line that uses a choke of about 100 micro-henries to keep noise out of your
transceiver. This L/C meter will tell you when you have wound the correct number of turns for the
inductance you need.
Even if you do not build the L/C meter the information herein may serve to give you some insight into
what is involved in homebrewing. Information provided on PCB fabrication may be of interest also.
First here is a list of steps I would normally take in doing a homebrew project.
Decide what project you want to undertake.
Choose the way you want to go: put together a kit or build from information from other homebrewers. If
you decide on a kit that suits your pocket and has the features you need then buy the kit and follow the
assembly instructions. All you need to know is how to use a soldering iron, a pair of pliers and side
cutters. This is the simplest way to go. If you want something better to enjoy and learn as you go along,
then go to step 3.
Gather as much information as you can. There is a vast amount of information on the Internet. Do not
dive in to the first project you find in the category you are researching. Do read texts off-line. Save all
the information provided on these projects and read through them during your leisure time. There are
many projects in the ARRL Handbook and other Ham publications.
Study all the different projects. Pick the one that most meets your requirements with respect to size,
cost, ease of construction, whether a PCB pattern is available, performance specifications etc. You
alone will be able to determine which features are "must haves", and which are "nice to haves". Your
choice will of course have the best "must haves" and the nicest "nice to haves". You may want to add in
ideas of your own. This is the time to do it. Record any modifications and changes you want to make.
Don't forget to modify the PCB if you do so. Be aware that some "April Fool's" projects can take on
identities that look genuine.
If a PCB pattern and overlay diagram is provided then rest is easy sailing. Open up the pattern and do a
test printout, on "plain" paper after resizing the pattern: http://www.keirle.fsnet.co.uk/print.htm.
Collect the parts according to the parts list. If there is no parts list you will have to make your own from
the circuit diagram. Check that all parts will fit into their pin spacing and allotted space. Usually, the
capacitors, especially electrolytics, are the ones that give trouble. In rare instances you may have to
check on an IC. The LM380 audio amplifier, for instance, can come in either an 8- or14-pin pinout.
Some operational amplifiers come in circular metal cans instead of DIL layout. Check the PCB pattern
before you purchase.
Fabricate the PCB. Check these links:
http://www.fullnet.com/u/tomg/gooteepc.htm and http://homepage.eircom.net/~ei9gq/pcb.html
Double check the PCB for any unetched copper that may cause shorts between traces. Check also for
breaks in the traces that may cause open circuits. Insert and solder in the parts using the overlay diagram
as a guide and the circuit diagram as a double check.
Always check that polarised components like electrolytic and tantalum capacitors, diodes, transistors,
three-terminal voltage regulators and ICs are correctly oriented. With all components installed, check to
make sure that there is no short across the points where the power supply is to be connected. If there is a
voltage regulator on board, check across the output of the regulator also.
If all is well up to this point you may connect the power source THE CORRECT WAY AROUND with
the power switch (if there is one) in the OFF position. At this point check again that the power leads are
correctly wired before you throw that switch. None of the polarised components mentioned above is
forgiving to anyone who commits the ultimate sin of connecting the power "the wrong way around", as
they say; and they will express their disapproval by their protest. You have been warned!
Switch the unit ON and check for any smoke, strange noises or overheating. Any component you can't
keep a finger on is overheating. If this happens switch the unit off and put your troubleshooting skills to
work. If the unit works, give yourself a pat on the back, run it through its paces and tell the rest of the
world how proud you are.
Now let us look at what I put into this L/C Meter project. The heart of the L/C Meter is a PIC16f84
Integrated Circuit from Microchip. : http://www.microchip.com/1010/index.htm
I first became aware of the PIC (Peripheral Interface Controller) in December of 1999 from the ARRL
So, once again, I turned to the Internet to satisfy my curiosity. I located PIC Tutorials that are available
free and saved them for study. Here are some of them.
http://www.tanzilli.com/pbe/italiano/: This is an Italian site with the first PIC tutorial I ever downloaded.
The translation to English took many hours spread over several months, but it was worth it.
In early 2000 I came across an L/C meter Kit being sold by a Company called AADE
Information on an L/C meter is here: (http://www.aade.com/lcm2binst/LC2Binst.htm). It uses one of
Microchip's PIC Integrated Circuits. The instruction manual that accompanies the kit was, and still is,
available for download. In the manual I found a circuit diagram of the unit, parts list, component
overlay and a description of how the unit functions, along with all the formulae necessary to calculate L
and C values.
All this relevant information was saved at that time for future use.
So having made the decision to phase out the C64, my plan A was to use AADE's circuit and work out
the PCB layout. In the meantime I kept an eagle eye out on the Internet. A few other designs were found
some using microcontrollers other than Microchip's PICs.
Somehow I kept thinking that Microchip's 16F84 was the best chip for me to use as a beginner. It can be
reprogrammed thousands of times and so lends itself to experimentation and facilitates easy correction
of mistakes in the software. The chip used by AADE (16C622) falls in a category called OTP (One
Time Programmable). You have one chance to program it. If a mistake is made in the software that's it -
the chip may not function as expected or it may not work at all. You have to program another one.
I spent many sleepless nights trying to work out a plan of routines to calculate inductance and
capacitance. Soon it dawned on me however that ordinary binary maths cannot handle fractional
decimal numbers like the value of Pi, for example, (3.14159265359). One has to resort to "Floating
Point Arithmetic", something of which I knew nothing.
Again, searches on the Internet showed up some routines used by some of the PIC gurus. I soon realised
though that this floating-point thing was a little bit beyond me and would require some intense brain
racking. I decided then to "give it a rest" but still continued my search on the Internet.
Then a few months ago I came upon this site (http://www.antrak.org.tr/gazete/111998/barbar.htm)
It had exactly what I was looking for. Unfortunately, it is a Turkish site but I was able to make sense
with a minimum of translation; and thus my Homebrew L/C meter project got a big boost.
The foregoing may seem a bit daunting to some. But let me explain here that this project, the L/C
Meter, is not a common project. The software is complex and the number of L/C meter projects that I
have seen on the Internet is small.
It is not necessary however, to know anything about writing programs for PICs. All you need to do is
procure the parts, fabricate the PCB, program the 16F84 chip from the software provided, populate the
PCB and solder in the parts.
Sounds easy? Of course it is!
Before I get into the real meat of the project, let me explain that there are different levels of
One may just purchase a Kit of parts and follow the assembly and testing instructions. This is the
simplest and easiest level.
One may follow a design provided by someone else (as I did in this case) by duplicating a PCB and
layout. Procuring parts in this case may be a bit more difficult depending on the size and quality of your
junk box. It may be necessary to substitute parts so that some knowledge of the function of the original
parts is important to make an assessment of the suitability of the substitute parts. In this case also some
knowledge of how the unit functions may be useful if it does not work when completed. A substituted
part may not meet the specifications of the original.
One may decide to do a project for which only a schematic diagram is available. This requires doing,
among other things, the parts layout and PCB artwork if a PCB is going to be used. Check here
http://homepage.eircom.net/~ei9gq/pcb.html; The Home Page for this site has good homebrew stuff
including a multi-band HF SSB transceiver. The VFO stabilizer and digital readout for my HF
homebrew transceiver came from this site.
Finally one may have the necessary skills, knowledge and time to design circuits "from scratch" as they
say. While this would be ideal it does not appear to attract the average Ham. After all why bother to try
to re-invent the wheel. The ARRL Handbooks and other publications provide sufficient examples of
Amateur Radio circuits and techniques. So does the Internet.
Let us now look at the project on hand.
This link provided me with what I needed, http://www.antrak.org.tr/gazete/111998/barbar.htm: The
PCB pattern presented at the site is a bit rough on the traces so I used a Macintosh application called
Graphic Converter and produced the pattern below. You may want to use Windows Paint.
The reworked PCB Pattern. Compare this with the one at the site.
1. This is the pattern that you will be transferring on to the copper side of the board so that after
etching the bottom of the PC board, called the" solder side", will have a pattern that is a mirror
image of the pattern above.
2. You may have to scale the pattern when printing to arrive at the correct size. You can check by
printing the pattern on ordinary paper and checking for the 3.5-inch dimension.
Another check is to place the 16f84 socket on the printed test pattern and see that the pins line up
with the holes. Note that the16f84 has a narrow-width 18-pin layout. See that you purchase the
correct socket. There is another 18-pin socket with wider pin spacing.
Use the component overlay drawing to assist in the placement of the components.
There are three Zipped files: LCM.ZIP, LCM_C84.ZIP and LCM_F84.ZIP. I downloaded all three and
unzipped them. The first file is for use with a PIC16C61, an OTP, the second is for a 16C84, another
OTP and the third is for a 16F84 which is basically a re-programmable version of the 16C84.
Keep the contents of each zipped file in a separate directory (folder). Though they may appear similar at
first glance, they are different. You have been warned. If you are going to build the meter the safest way
to go is to decide which chip you want to use and only unzip the file for that chip. I chose the 16F84 for
reasons I explained before.
Unzipping each file generates six files. The three main files of interest for anyone wishing to program
their own chip are the ones called LCM.ASM, LCM.H and LCM.HEX. Check the Tutorials for more
So, having put my PCB pattern onto glossy paper using the toner method, I used heat to transfer the
artwork on to the copper. The etching process came next.
The pictures below show the result of these two steps.
PCB1 shows the artwork transferred to the copper before the etching process. PCB2 shows all the
unwanted copper etched away leaving the copper pattern under the resist (toner). The light-coloured
spots seen on the pattern are residual spots of paper still adhering to the toner; they do not affect the
copper traces and are easily removed along with the toner etch resist.
After removing the toner and while the copper traces are still bright and shining, you may want to tin all
the copper with solder to keep the copper from becoming tarnished. At this point you can start
populating the PCB with parts.
The following pictures were taken without the front panel and housing for the meter.
Here is a view of the component side of the PCB, without the display.
The picture on the left shows the parts installed on the component side of the PCB. I did not have the
reed relay so that the mounting holes remain empty. A substitute relay was installed on the copper side
of the board and is not visible from this picture.
At the top left is the 14-pin male header onto which goes the intelligent display. The picture on the right
is a view of the back of the display with a 14-pin female socket installed.
These pictures show the PCB fitted with the display. The one on the left is the first screen displayed on
power-up as the meter goes through its initialisation. It then does an automatic self-calibration lasting
for two seconds and then displays the final screen.
The meter is then ready to be used and displays this screen.
Here are a couple of shots of the meter doing its thing
Measuring a 1000pf, 1% capacitor. Measuring a 100 micro-henry choke, tolerance
Measuring a random-wound homebrew coil.
The parts list for this project is the same as that for the L/C Meter IIB by AADE except for the PIC
chip, the crystal and the reference capacitor which in this case, is 1000 pFs and not 1020 pFs . The
crystal is a 4mHz unit instead of 8Mhz as in the AADE meter. The parts list does not appear on the
Turkish site. Most of the parts may be available here http://www.digikey.com/, but I have not checked
If you do this or any other project for that matter, it is wise to obtain all the parts before doing the
artwork and drilling the board. ----- Some components of similar value but made by different
manufacturers may have a different pin spacing. That capacitor you bought may not be identical to the
one specified by the author of the project.
The only component I did not have on hand was the reed relay. I had to do a substitution and had some
problems with it. I kept getting both C and L readings that were way off. I could hear the relay
operating, or so I thought, judging from the "click" when the meter went into the "calibrate" mode. In
this mode the relay switches in a 1000pf capacitor across the oscillator tank circuit and uses the change
in frequency to determine the tank capacitor and inductor values. The capacitor is then switched out. I
spent many hours trying to figure this one out and even resorted to programming another 'f84 chip. I
even tried another relay of the same type. I then decided to have a look at the frequency changes when
the relay operated.
I was shocked to find out that there was no change in frequency when the relay "operated". Without that
frequency counter I might have been still been trying to figure out where I went wrong. Installing a
different relay solved the problem.
This little anecdote serves to highlight two points:
It pays to have an understanding of how the circuit functions
As a good friend of mine always says, "to measure is to know".
By the way, the frequency counter seen in one of the pictures is a 600 MHz homebrew job, built from a
construction article that appeared in a Radio Electronics magazine of many years ago. Today a 2GHz
frequency counter can be built on a PCB that is about two-thirds the size of the L/C meter board.
Thanks to microcontrollers.
You may have noticed that this project was probably inspired by AADE's L/C meter IIB which has
better specifications. It appears to me that all that is needed is to program a 16C622 chip, replace the
16F84 with it and use an 8MHz crystal and one will have an L/C Meter IIB. This I will try. The PCB
pattern and the basic schematic diagrams are identical.
Take a look at this report: http://www.antennex.com/preview/Folder04/Oct501/lcmeter.html
If you decide to embark on this project and all goes well you should have a piece of test equipment that
you would be proud of.
If you have any comments or questions please drop me a line.
My next project will be an ESR (Equivalent Series Resistance) Meter for measuring, in circuit, the ESR
(not value) of those failing electrolytic capacitors especially in Switchmode Power Supplies without
having to remove them from the circuit board.
This is a much simpler project than the L/C meter, using a quad opamp and a small double-sided PCB
that is about 1/4 the size of the L/C meter PCB.
For measuring the value of electrolytic capacitors I already have a homebrew meter that spans from
100pFs up to 10,000 uFs.
In the meantime guys, have fun homebrewing.