Making: A $20 Parts-Meter & How to Use It

If you’re into robotics, computers, electronic circuit design, fiddling, or you’re a ham radio hobbyist wanting to spend more time on the boss end of a soldering iron, my friend Jeff at the local ham club turned me on to something called an “M-Meter, parts meter and assorted other names.”

What makes this a useful tool is it answers one of the more troubling problems face by newcomers to electronics;  which is “Just what it this damn part I’m looking at?”

“Pretty cool, too,” I was assured. “Just plug a part in and it will tell you what you’ve got!”  Given the number of eye operations I’ve been through, anything that lightens the load on the eyes is “all good.”  Besides, the Parts or M-Meters are dirt cheap – about $11-bucks on eBay for the working board and I splurged for an $8 acrylic specially-made box to put it in.

(*Continues below)

The first step in assembly is to lay out the case parts to get an idea of how things to together.  There’s a QR code on some of the packaging.  But, while the Chinese may believe all American’s own iPhones, there are those of us on slow circuits and out of cell-range in the woods.  I already warned you some tablets – like my new Kindle HD 10 will not focus close on small QR’s, right?  Still, it’s an enclosure for crying out loud — how tough could it be?

Essentially, you get two big pieces of clear acrylic.  The one with the plentiful screw holes is the bottom, while the one with the cutout for the component test-bed goes on top.  Not hard stuff.

Just remember that on the two long side pieces, there’s one with a cut-out and this is placed adjacent to the top where the test socket (and lever) are located.  The side cut-out lets the lever move to the locked position.

There are four long screws and nuts;  also four screws that are short with nuts.  The short one are used with small plastic stand-offs to hold the CPU/ display board off the case.  Eventually (since rocket science is what we do around here, yeah?) I figured the four long screws with nuts would clamp the case together.

After using those untrimmed fingernails (no one who actually makes things trims their nails, I tell yah) the paper is off the plastic parts (they look water-jetted) and you’re ready to, er, screw.

The standoffs go under the printed circuit board (PCB) and they will only fit one way with the holes lined up…

If you look closely, you will see that Ure’s truly has spread out a micro fiber cloth to work on.  Several reasons for this:  Acrylic scratches if you so much as look at it crooked.  I buy large packs of the micro fiber towels from Amazon.

Micro fiber clothes are cheap:  $10-bucks for 25: S&T Bulk Microfiber Kitchen, House, & Car Cleaning Cloths – 25 Pack, 11.5″ x 11.5″. These come in multiple colors.  Which I use for different projects.  Yellow and green are for electronics, other colors are for automotive and milling and metals.  Adds to my delusion that my shop is orderly and organized…

While getting fingerprints of hot vacuum tubes (which can cause hot-spots on high power tubes) these micro fiber god-sends are perfect finger-print getter-offer for all things plastic.  A quirt of Plexus Plastic cleaner ($19, but great to have on hand for all things plastic) and it will look like new.

Did I mention that the dropped tiny screws are easier to find when you drop them on a yellow micro-f shop towel? (Gotta do something about my floor, lol.)

Just before the top cover goes on the parts meter, don’t forget to toss in a really fresh 9-volt battery.  Although the unit is simple enough to hold together (after you’ve gone through the dropping curve to hold the case together while putting in screws and nuts one-handed because you’re too lazy to get the masking tape to help…) this is not something you want to plan as a centerpiece when entertaining.  Repeat after me: PITA. Get the masking tape to hold things together and then remove.

How Does It Work?

Cool!

In Ure’s Lab, all the pill bottles I’ve ever handled live in some semblance of order.  So, I was able to quickly pick some difficult projects for the parts meter.  I wanted to see just how good it with do with this and that:

Can we bring out our first candidate, please?

If you squint at the lower corner of the meter, you will see it is 10.13 nano farads which is what the part is labeled in my (surprisingly neat) parts collection.

You just need to remember on capacitors there are conversions to get from micro farads to nano farads, to pico farads, which is newspeak for micro-micro farads which is redundant redundant!

It’s just that there are three ways to state something like capacitor value on older schematics of radios, robots, and whatever:  In this case, the choices are 0.01uF / MFD,  the 10nF nano farads, or the 10000pF (MMFD) where MMFD really means uuf (now pico farads) if you’re a grown up.

Doe it work on all values tried?  No.

Had something of an issue with small capacitors like 47 uuf,  (47 pf).  BUT it got the small chokes (inductors) about right – and that’s what it will be used for.  Inductors, also called “coils” or “chokes” have a color coding system 300-feet past stupid when your eyes are sub-Optimus Prime.

Come to think of it, lots of components are little Decepticons.  What the hell is a capacitor vale (disk ceramic) of “103???”

A dandy article over at Robotoid here goes into this occult other-earthly capacitor language.  Or, you plug the part into the meter like this just-assembled parts meter  and out pops the answer.

Is it the be-all, end-all?

Far from it, eventually you will end up with a sizeable meter collection that will eat up most of your bench space if you don’t keep them locked up and prevented from reproducing.

Left to right:

The first meter is the new parts meter.  This will take a stab at playing “Name that component.”

Second one is an Equivalent Series Resistance (ESR) meter.  This will take a whack at capacitors including (with a dozen asterisks) in-circuit caps with 50 asterisks.  One of which is that table on the front of it which requires a magnifier for older techs like, uh…you know!.

Meter #3 is used when you don’t believe the ESR meter.  It’s a pure capacitor meter, BUT it will go wonky on some capacitors (big broadcast silver-micas don’t read well, for example).  Unsolder one end of the capacitor you’re wondering about because it doesn’t do in-circuit well..

The last meter is a simple transistor and IC checker.

“How Many Meters Do You Need?”

Dang!  That is a toughie.  If you are doing “simple” robotics, then a “grown-up” meter with a current clamp, probes, holster, and all that makes sense.  Take out $235 and get a Fluke 117/323 KIT Multimeter and Clamp Meter Combo Kit.  But, what about inductance?  Try the on-sale for $11 Digital Multimeter, HOLDPEAK 4070L Manual-Ranging Multi Tester for Measuring Resistance?Capacitance, Inductance, Transistor, hFE of 2000 Count (Blue).

When people ask me “why so many” I use the water analogy to electricity.  Voltage is like the water pressure.  Current is like the cubic volume of water flowing.    The “pressure” (volts) times the “amount of current flow” (amps) gives you the amount of “work being done” (in Watts).

Ergo, voltmeters, ammeters, and watt-meters.  This “parts meter” is really an inexpensive subset of LCR (inductance, capacitance, resistance) meters.  There are lots of them available with the main feature change being whether the unit is auto-ranging or if you have to spin a switch to find a reasonable reading.

Measuring Alternating Current (AC) Voltages

When messing about making things, we have Alternating Current (AC) as well as Direct Current (DC).

It’s not so simple as you’d think:  Alternating current (AC) has two major ways of being measured:  One way is “peak-to-peak.”  This is from the top of one cycle to the bottom of it.  Assuming symmetry…another longish debate,  Peak-to-Peak reading.

Unfortunately, while it’s true that Peak Volts and Peak Amps will multiply into a number giving Watts (instantaneous work done), the REAL number in the power world is called RMS – stands for root-mean-square).  You use RMS to get to average work done,.

DON’T USE THE PARTS-METER in today’s project to test AC lines!!!  Use a real meter – Fluke 117.  Insulation matters!

So, if you (CAREFULLY WITH EXPERIENCED SUPERVISION) stick a peak-reading AC volt meter into a dryer plug you might find peak to peak is 339 volts.  To convert this to RMS, you multiply times 0.707 and THAT is what the power company will bill you on.

EXCEPT even THAT refined number is not really a pure one.  Because of something called “power factor.”

Regulators (does the term “lying lazy pieces of crap” come to mind here?) have been sold the idea that utilities should bill everyone on the basis of a power factor of 1.

What this means, without going into the engineering side too deeply, is that it the power company is allowed to ASSUME that peak current and peak voltage arrive at your appliances at the same time.

They don’t – not in the real world.  When the peak current shows up at a different time than peak voltage, you may pay for one kilowatt-hour of work and only really get 0.80 kilowatt hours!

Think about this closely. If the current and voltage are totally out of phase:  Peak voltage arrives when there is ZERO current, so no work will be done.  Since 240 volts times ZERO amps in this worst case nightmare is zero amps, the dryer won’t dry clothes well.

Same thing other way around:  If peak current arrives with zero volts….

Back to the robotics angle:  This power-factor discussion is not academic.  Because in robotics the easiest way to control power is using pulse width modulation.  PWM.

Instead of nice, smooth sine waves like come out of your wall, PWM robotics controllers slice or chop Direct Current on and off.  For light loads, it’s a paper thin slice of voltage.  For a heavy loads a bigger ‘slice of power’ is used.  Think of PWM as different thicknesses of sliced breads.  Thin slices give you less energy..

For complex power (PWM) you won’t use a parts meter or even an LCR (unless looking for a faulty component).  the right tool for complex wave forms is an oscilloscope.

That’s beyond the discussion in this week’s making oof stuff, but the point is, you need as many meters as you’re planning to mess about with.

If you cover from DC to AC daylight?  OMG.  Not only will you need volt and current (and capacitor and component) (LCR) meters, but you will need precision voltage sources to test and calibrate things. And an oscilloscope.

At the end of the day only simple questions remain:  How much precision and over what kind of range?

The ultimate limiting factor – though seldom stated – is “How much are you willing to afford?“”  There’s always like any other hobby, if you have the money, someone’s got something really cool to sell you.

Test equipment for messing about is no different.

Now, off to play with the ham radio:  “Computer: turn on the tunafish!”  (See the Coping section on voice automation hell this week….got it worked out, lol.)

Write when you get rich,

George@ure.net

George Ure

Amazon Author Page: https://www.amazon.com/George-Ure/e/B0098M3VY8%3Fref=dbs_a_mng_rwt_scns_share UrbanSurvival Bio: https://urbansurvival.com/about-george-ure/

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