Testing circuits with a multimeter is exciting

How to Use a Multimeter: Repair a Circuit

For this month’s post, we’re going to show you how to use a multimeter.

We live in a world where electronics are everywhere. They connect us and work wonders that would have been inconceivable a generation ago. 

And sometimes they break.

They get thrown out and maybe replaced.

Have you ever wished you could figure out why a kid’s favorite toy stopped working? Or perhaps you’ve tried to wire up a simple circuit but didn’t manage to get the darned bulb to light up? 

Maybe you thought there should be some way to figure out why that little mess of wires isn’t behaving as it ought to?

That’s when we break out the multimeter (also called a voltmeter)!

They might look complicated at first, but with a little guidance they’re actually really easy to use.

We’ll demonstrate by using a Fluke 322 multimeter, which is similar and works the same way as most other comparable multimeters.

We’ll show you the parts of the multimeter and how to use its different functions.

Then we’ll show you how to use a multimeter to diagnose the problem with a mystery circuit.

We’ll demonstrate how to use a multimeter to test voltage, how to use a multimeter to test resistance, and how to use a multimeter to test continuity. 

Before getting started, if you’re not already familiar with basic electronics concepts, you may want to check out this post on electrical current, resistance, and voltage.

Here’s everything you need to master your multimeter and take control of those problem circuits! 

You can check out our video tutorial here and subscribe to our YouTube channel to keep up with new projects.

Everything is explained below as well (but you have to watch if you want to see what the mystery circuit does at the end!).

Controls on a multimeter

Fluke 322 multimeter

The dial on the multimeter lets you select what you want to measure. Simply turn the dial until the little dot on the dial lines up with the function you want to use.

The V at the top with the straight and dotted lines indicates direct current (DC) voltage.

The V with the wavy line is for alternating current.

Direct current is current that only flows in one direction, like out of a battery. Our homes, on the other hand, are wired for alternating current, which changes direction many times every second. 

Continuing down the dial, we see the setting for measuring resistance, as shown by the horseshoe-shaped omega symbol (Ω).

Next, the A with the wavy line is the setting for measuring alternating current, which is done with the large red clamp on top of the multimeter. Since our projects are powered by a battery’s direct current, we won’t demonstrate that in this post. 

The final position on the dial turns the multimeter off. 

The hold button freezes the display reading.

Jacks at the bottom are for plugging in the probes that we touch to different parts of the circuit. They can plug right in – red to red and black to black.

Fluke multimeter jacks

How to use a multimeter to diagnose the problem with a circuit

Supplies

Fluke 323 meter

Electronics to test such as batteries, resistors, copper wire, and electronic circuits.

Steps

Step 1: How to use a multimeter to test voltage

Step 2: How to use a multimeter to test resistance

Step 3: How to use a multimeter to test continuity

Step 1: How to use a multimeter to test voltage

To demonstrate how to use a multimeter to test voltage, we can measure a battery’s voltage. 

(And next time you aren’t sure if a battery is dead, you’ll know how to check!)

A big difference between a higher-end multimeter like this Fluke model and the less expensive multimeters is that you don’t have to specify the range of the voltage you want to measure. These fancier models are autoranging. 

So, just go ahead and set the dial to DC voltage (the V with the straight line). Then, touch the red probe to the positive battery terminal and the black probe to the negative terminal.

We measured the voltage of a battery pack with 2 double A batteries wired in series. Since each double A battery has a voltage of 1.5 volts, the combined voltage should be 3 volts. 

As you can see, the meter reads 3 volts, just like we expected.

Testing voltage

With this multimeter it’s not a problem if we reverse the probes and connect red to negative and black to positive. If we connect the probes in reverse, we measure negative 3 volts.

Step 2: How to use a multimeter to test resistance

To use the multimeter to test resistance, we start by turning the dial to the resistance setting (the horseshoe-shaped omega symbol, Ω). 

With an inexpensive model you’d also have to specify a range, but we don’t with this Fluke meter.

We’ll demonstrate how to do this using a clearly-labeled 100 ohm Snap Circuits resistor. 

If we touch a probe to each end of the resistor, sure enough, we see that our reading matches the expected resistance.

how to use a multimeter to test resistance

Step 3: How to use a multimeter to test continuity

We can measure resistance of more than just resistors. 

In fact this is how we can test continuity in a circuit. 

Where we expect that there’s a break somewhere in a circuit, we can measure resistance at different locations in the circuit to home in on where the bad connection is.

Where resistance is low enough to allow the electric current to flow, the multimeter will beep.

Where there is a break in the circuit between the probes, the multimeter will not beep.

On this circuit, the multimeter beeped when we touched the probes at these points:

How to use a multimeter to test continuity

And it also beeped when we touched the probes at these points:

Testing continuity with a multimeter

But the probe did not beep when we touched it at these points:

Measuring continuity to find the bad connection in a circuit

And when Eric examined the problem spot, he found that the boys had put a piece of tape between the circuit connectors to break the circuit!

By taking out the tape and snapping the pieces back together, Eric was able to repair the circuit.

Of course, continuity testing can be helpful for lots of different circuits (not just projects built with Snap Circuits pieces). This is exactly the way we found a bad solder joint in a broken remote control. After we resoldered the joint, the toy was as good as new.

And if you need help learning how to solder, you’ll want to check out next month’s post, where we’ll show you how it’s done.

If you found this post helpful or have questions, please let us know! Are there other projects you’d like us to build? Please leave us a comment!

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