Kit review – High Accuracy LC Meter

Hello readers

Time for another kit review. Lately one of my goals has been to make life easier and in doing so having some decent test equipment. One challenge of meeting that goal is (naturally) keeping the cost of things down to a reasonable level. Unfortunately my eyesight is not the best so I cannot read small capacitor markings – which makes a capacitance meter necessary. Although I have that function within my multimeter, it is often required to read resistors in the same work session.

Thus the reason for this kit review – the High Precision LC Meter kit. The details were originally published in the May 2008 issue of Australia’s Silicon Chip magazine. The meter specifications are:

  • Capacitance – 0.1pF to over 800 nF with four-digit resolution;
  • Inductance – 10 nH to over 70 mH with four-digit resolution;
  • Accuracy of better than +/- 1% of the reading;
  • Automatic range selection, however only non-polarised capacitors can be measured.

The power drain is quite low,  between 8 (measurement) and 17 milliamps (calibration). Using a fresh 9V alkaline battery you should realise around fifty to sixty hours of continuous use. At this point some of you may be wondering if it is cheaper to purchase an LC meter or make your own. A quick search found the BK Precision 875B LCR meter with the same C range and a worse L range for over twice the price of the kit. Although we don’t have resistance measurement in our kit, if you are building this you already have a multimeter. So not bad value at all. And you can say you built it :)

Speaking of building, assembly time was just under two hours, and the kit itself is very well produced. The packaging was the typical retail bag:

retailkitss

The first thing that grabs your attention is the housing. It is a genuine, made in the US Hammond enclosure – and has all the required holes and LCD area punched out, so you don’t need to do any drilling at all:

hammondcasess

The enclosure has nice non-slip rubberised edging (the grey area) and also allows for a 9V battery to be housed securely. The team at Altronics have done a great job in redesigning the kit for this enclosure, much more attractive than the magazine version. The PCB is solder-masked and silk-screened to fine standard:

pcbss2

There are two small boards to cut and file off from the main PCB. We will examine them later in the article. All required parts for completion were included, and it is good to see 1% resistors and an IC socket for the microcontroller:

partsss1

At first I was a little disappointed to not have a backlit LCD module, however considering the meter is to be battery operated (however there is a DC socket for a plugpack) and you wouldn’t really be using this in the dark, a backlight wouldn’t be necessary. Construction was easy enough, the layout on the PCB is well labelled, and plenty of space between pins. Lately I have started using a lead-former, and can highly recommend the use of one:

leadformerss

Assembly was quite simple, just start with the lower profile components:

assemble1ss

 

… then mount the LCD and the larger components:

assemble2ss

… the switches and others – and we’re done:

finishedsolderingss

The only problem at this point was the PCB holes for the selector switch, one hole was around 1mm from where it needed to be. Instead of drilling out the hole, it was easier to just bend up the legs of the switch and keep going:

switchlegsss

At this stage one has to cut out two supports from the enclosure, which can be done easily. Then insert the PCB and solder to the sockets and power (9V battery snap). Initial testing was successful (after adjusting the LCD contrast…

inittestss

If you look at the area of PCB between the battery and the left-hand screw there are eight pins – these are four pairs of inputs used to help calibrate and check operation of the meter. For example, by placing a jumper over a pair you can display the oscillator frequency at various stages:

calibrationss

Furthermore, those links can also be used to fine-tune the meter. For example one can increase or decrease the scaling factor and the settings are then stored in the EEPROM within the microcontroller. However my example seemed ok from the start, so it was time to seal up the enclosure and get testing. Starting with a ceramic capacitor, the lowest value in stock:

3p9pfss

Spot-on. That was a good start, however trying to bend the leads to match the binding posts was somewhat inconvenient, so I cut up some leads and fitted crocodile clips on the end. The meter’s zero button allows you to reset the measurement back to zero after attaching the leads, so stray capacitance can be taken into account.

Next, time to check the measurement with something more accurate, a 1% tolerance silvered-mica 100 picofarad capacitor:

99pfss

Again, the meter came through right on specification. My apologies to those looking for inductor tests – I don’t have any in stock to try out. If you are really curious I could be persuaded to order some in, however as the capacitance measurement has been successful I am confident the inductance measurement would also fall within the meter’s specifications.

As shown earlier, there were two smaller PCBs included:

pcbadaptorsss

The top PCB is a shorting bar used to help zero the inductance reading, and the lower PCB is used to help measure smaller capacitors and also SMD units. A nice finishing touch that adds value to the meter. The only optional extra to consider would be a set of short leads with clips or probes to make measurement physically easier.

When reading this kit review it may appear to be somewhat positive and not critical at all. However it really is a  good instrument, considering the accuracy, price, and enjoyment from doing it yourself. It was interesting, easy to build, and will be very useful now and in the future. So if you are in the market for an LC meter, and don’t mind some work – you should add this kit to your checklist for consideration. It is available from our store – Tronixlabs.com

 

visit tronixlabs.com

… which along with being Australia’s #1 Adafruit distributor, also offers a growing range and Australia’s best value for supported hobbyist electronics from DFRobot, Freetronics, Seeedstudio and much much more.

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John Boxall

Founder, owner and managing editor of tronixstuff.com.

18 Responses to “Kit review – High Accuracy LC Meter”

  1. Lokhin says:

    LC metr очень практичен. Выполняет в высоком % измерения и удобен в производстве ремонта. Большое спасибо за предоставленный обзор. Имею желание пользоваться.

  2. noozillander says:

    Thanks for the great revew John. Much apprecated.
    Have just bought ths kt n NZ, on the bass of your revew.

  3. David Bradley says:

    H John great artcle have bought kt from Alltroncs,lookng forward to buld,wondered where you got your lead former ,many thanks Dave

  4. Rapsod says:

    Where dd you get lead-former tool?

  5. Steve May says:

    H John,
    Thanks for the knd revew.
    We also lke the way the kt turned out n the hammond case.
    The problem wth the swtch holes wll be looked at and addressed.
    On your recommendaton we wll also nclude one of our banana plug to crocodle clp leads n future runs of the Kt.
    Thanks agan.
    The Team @ Altroncs

    • John Boxall says:

      Hello Steve
      Thank you for readng and takng note of the revew ponts, t’s great to know that a local company s lstenng and cares about such thngs :)
      Keep up the great work
      cheers
      john

  6. Juliean says:

    Anyone know of a US retaler for these?

    • John Boxall says:

      Altroncs s an Australan company who produces the kt. They should be able to export one to you. If not, I can do ths for you at cost f you lke.
      Cheers
      john

      • Juliean says:

        I’m sure they can do t, was hopng to avod dealng wth nternatonal shppng. Wll probably emal them to see f they have us retalers, was just hopng someone mght know off hand.

  7. Ben says:

    Can you tell us what the test frequency s? Most L meters do not test at audo frequences and are thus not sutable for measurng nductances n audo equpment and electronc nstruments.

    • John Boxall says:

      I’m between houses so t’s n storage wth the documentaton for a few more weeks so I can’t look t up. The nternet ddn’t come up wth the answer ether. Perhaps ask the Altroncs kt department va here – http://www.altroncs.com.au/ndex.asp?area=cont
      john

    • Brett says:

      H Ben,

      The meter sets up an LC crcut wth nternal reference components and the part under test.
      Ths s what gves the meter ts accuracy, It leaves the frequency as the measured varable that changes wth the value of the part under test.

      The equatons for the operatng frequency are n the nstructon manual.
      Measurng very small values of capactor, the frequency can be as hgh as 160KHz
      Measurng a 10uF cap, that falls to 5KHz.

      Kt Manager,
      Altroncs.

      • Ben says:

        Thanks Brett!

        The problem s my Fluke 115 s a great multmeter, except when t comes to measurng nano- and pcofarad-range capactors or an nductor (no L measurng ablty). Whch s the reason I purchased an “L/C” meter kt a couple years back. You can magne how dsapponted I was to dscover that t was only accurate measurng L n the MHz range (sutable only for RF work).

        What I would need to see the Altroncs meter do s accurately measure the nductance of some known value nductor that would be used n audo, such as a 2.5mH nductor you mght fnd n a speaker crossover. Or the L of a gutar pckup, or a tube plate choke (reactor); somethng of that nature.

        What I don’t need s a *thrd* capactance meter.

        Best to you,
        Ben

  8. Ray Miller says:

    Very professon kt but had some problems wth the reference oscllator stoppng sometmes, C3 (especally) and C9 10uF capactors both need to be low Z at 600kHz usng ether tantalum or low ESR electrolytc fxes the problem. On the battery sde I substtuted for REG1 7805 a LDO regulator LP2905ACX and the battery current dropped to <3ma (from about 20ma), smple cheap and sgnfcant battery savng.
    Cheers Ray

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