How To Use a Multimeter to Measure Voltage, Current and More

Inexpensive, essential tool can test circuits, resistors and batteries for your projects.

Electronics is an amazing subject, there’s a lot to learn, and many fascinating projects to create. To do this you would think that you need thousands of dollars of equipment, but you can do a lot with very little. All you really need are the tools to get you started. a Raspberry Pi Pico, side cutters, pliers and a soldering iron are some of the most versatile tools for the budding electronics enthusiast.

But no matter what level of maker you may be, we all need a Digital Multimeter. A multimeter enables us to make accurate measurements of both current and voltage, can help us test and debug circuits by checking continuity and can help us identify component values.

In this how to we shall take our first steps with this essential tool. Learn how to safely use it when taking readings in circuit, and to check components.

Multimeters, like many products, come in a range of styles and price ranges and even the most budget options offer lots of functionality. For around $15 you can pick up a basic multimeter good enough for hobbyist electronics. Most multimeters are designed to measure DC and AC current, but it’s important that you know your own knowledge limits and don’t interact with mains AC voltages.

US mains voltage is around 110-115V, in the UK it is around 230-240V, and both of these are enough to severely injure you, possibly even fatally. Never interact with mains voltages unless you know what you are doing, or have the supervision of someone who does. If you intend to utilize mains voltage in a project, a $10 multimeter is not good enough, and you should research for a multimeter that meets the safety requirements of your country. For this how to, a $10 multimeter for battery powered/low voltage applications is a great way to learn.

Multimeters have the ability to measure DC and AC voltage, current and resistance. Beyond that, there are heaps of useful features that you might consider looking for in a multimeter. Often these features are hidden behind a myriad of symbols. It’s worth looking at the instruction manual of your multimeter to work out where all the different functions are.

It’s worth considering a few extra features when choosing a multimeter. A backlight is often useful, making the display easier to read. A fold out stand will enable the multimeter to be used on a desk.

Multimeters have a set of test probes that plug into sockets on the main body of the multimeter. The most common probes bundled with a multimeter have a plastic body and metal pointed tips. The tips are placed in contact with your circuit or component to take a measurement or perform a test. These standard probes are perfectly adequate for the majority of uses, but you may opt for a model with additional useful probes. Other useful probes include micro hook probes which allow you to clip a probe onto a component lead and then not have to hold the probe, or similarly some probe wires have simple crocodile clips on the end of them. Additional probes can be purchased quite easily via Amazon or electronic resellers.Probes can come with different amounts of insulation. Insulation right up to the tip is safer when probing your project, but might make the probe thicker and harder to access tight spaces. On some probes we can remove the covers, exposing the thin metal tip of the probe. For low voltages these are relatively safe, but never remove insulation from a probe designed for high voltage use. That insulation is there to protect you!

Digital multimeters tend to fall into two basic camps: manual range multimeter and auto ranging multimeters. Both look quite similar but the key difference is that to use a manual range multimeter you need to roughly know the order of magnitude of the target you wish to measure as the multimeter has predefined ranges selectable by switches.

For example, let's set a manual multimeter to read a 9V DC voltage.

1. Turn the dial on the multimeter to read a DC voltage. Look for 20V and turn the knob to select. If you used this setting to try and measure a 40V project the multimeter would run out of range and you would get an error message on screen, typically 0L or 1.

2. Touch the black probe, connected to COM on the multimeter to the negative (-) terminal of the battery.

3. Touch the red probe, connected to the DC terminal of the multimeter.

4. A reading will appear on the screen. This is the voltage of the 9V battery. This voltage could be higher or lower depending on the age and state of the battery.

The same process for an auto ranging multimeter is slightly easier, as you may guess, An auto ranging multimeter automatically changes its range as it detects the value of the measurement at the probes. This has an advantage in that you don’t need to know the range in advance but the slight cost is that it may take fractionally longer for the display to settle on a reading. However, auto ranging is very convenient and can also help you quickly identify resistor values. That’s particularly of use if you have a visual impairment that makes it difficult to read resistor color band codes.

1. Turn the dial on the multimeter to read a DC voltage.

2. Touch the black probe, connected to COM on the multimeter to the negative (-) terminal of the battery.

3. Touch the red probe, connected to the DC terminal of the multimeter.

4. A reading will appear on the screen. This is the voltage of the 9V battery. This voltage could be higher or lower depending on the age and state of the battery.

Let’s look at the basics of using a multimeter by creating a small test circuit and taking some measurements. Our circuit is simply a 9V battery, a 220 ohm resistor and an LED.

1. Insert an LED into the breadboard. Make a note of which side has the longer leg.

2. Insert a resistor into the breadboard so that one leg is in the same row as the long leg of the LED.

3. Connect the red wire of the battery snap terminal into the same row as the remaining resistor leg. Then connect the black wire to the same row as the LED’s remaining leg. The LED will now light up.

Measuring current in a circuit is very useful and can help us to create efficient projects. When measuring current in a project, we need to change the probe connections on the multimeter and insert the multimeter in series into the circuit, essentially making the multimeter like a wire in the circuit.

The black probe will stay in the common socket but the red probe will be moved over to one of the current sockets. Many multimeters will have two sockets for measuring current, one for smaller currents and one for much larger. These sockets should be fused so that if accidentally you measure a circuit with too much current the fuse will blow and offer some protection to the user. Again, you should practice on small low current battery powered circuits and build up experience.

1. Remove the red probe from the multimeter and insert it into the mA socket of the multimeter.

2. Select the A⎓ mA setting on your multimeter. Manual multimeter users should look for the correct range. If in doubt, start too high and work downwards.

3. Remove the GND wire (black) from the breadboard and connect it to the black probe, connected to COM on the multimeter. You can wrap the bare wire around the metal tip of the probe but for best results use a crocodile clip test probe to grip the wire.

4. Touch the red probe to the short leg (cathode) of the LED. The LED will light up.

5. The current will be displayed on the multimeter display.

A simple, but handy use of the continuity checker, is using it to check if a length of cable, or one of your breadboard jumper wires, has a break in it. If you touch each end of the wire and it doesn’t bleep then you have detected a fault!

1. Take a length of wire with the ends stripped to expose bare wire.

2. Ensure that the red probe is in the voltage socket of the multimeter.

3. Place the black probe on one end of the bare wire.

4. Touch the red probe to the other end of the bare wire. The multimeter will beep to confirm continuity.

Resistors come in all shapes and sizes and also come in a huge range of values and it’s important to pick the right one for each project. Larger through hole style resistors have a color code system where there are bands of different colors printed onto the component package. You can decode these color bands to tell you the resistance value and the tolerance value of that resistor.

An auto ranging multimeter can be very useful in identifying the value of a resistor. Again the multimeter probes need to be in the voltage configuration and then you simply place a probe on either component lead of a resistor and the display should settle to give you a resistance reading. Resistors are not affected by polarity so it doesn’t matter which way around you connect the probes.

1. Remove the 220 Ohm resistor from the test circuit.

2. Set the multimeter to measure resistance (Ω). Manual multimeter users will need to set the correct range.

3. Touch the red probe to one end of the resistor. It doesn’t matter which end, resistors have no polarity and so current can flow in either direction.

4. Touch the black probe to the other end of the resistor.

5. The display will show the resistance of the resistor. In this case we can see that our resistor has a value of 220 Ohm.

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Jo Hinchliffe is a UK-based freelance writer for Tom's Hardware US. His writing is focused on tutorials for the Linux command line.

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