The Many Uses of Digital Multimeters

By Jo Hinchliffe / Best Practices / June 2022 Issue

You will be amazed by all the things you can do with multimeters!

Electronics projects are great and you can learn a huge amount, and make lots of interesting circuits with cheap components and very few tools. As you develop you might think that you need a fully equipped laboratory with all kinds of specialized equipment on your workbench but you can do a lot with very limited equipment. One of the first items that’s extremely handy; after perhaps some pliers, wire cutters and screwdrivers, is a budget digital multimeter.

Digital Multimeters (often referred to as DMM) are incredibly handy and can take a huge variety of measurements that can be useful to you in your electronics projects. In fact most of them do so many things we can’t cover everything that they can do! Let’s look at some of the ways a DMM can be useful in your project.

Most DMM have two probes plugged into sockets, one black and one red signifying positive and negative. Most of the time your probes will be connected to 2 sockets that are marked XXX which means that the DMM is set up to measure voltages and other items, but not current which requires the DMM to be connected to circuits in a different fashion, more on that later.

A really common use for multimeters in electronics projects is for measuring DC voltage. Say you have connected up a breadboard experiment, and then hooked up a battery but the experiment hasn’t powered up, your first thought might be to check the battery. Setting the multimeter to DC mode and holding the probe tips to either end of the battery will show the battery voltage, which may indicate that your battery needs replacing. Likewise you might also use the DC voltage setting to probe different parts of your circuit to look at the voltage in different areas. Keep the black probe connected to the negative end of a battery and then use the red positive probe to explore the voltage in different areas.

DC voltage measurements can also sometimes have other uses. One that we use often is to check the polarity of items. A good example is that some batteries come without distinguishing features at either end and it can be difficult to work out which end is which. If you are measuring the voltage of such a battery, say a 18650 cell with no marking, if you connect the positive probe to an unknown end of the cell and it turns out to be the negative end all that will happen is the battery voltage will be presented as a negative value. This will still give the correct numerical value of the voltage but will tell you that the probes are connected back to front, this means you can correctly identify the polarity of the battery.

If you have tinkered with electronics you will have come across the use of resistors. Resistors have stripes on them of differing colors which you can decode the value of the resistor in ohms. This is a fun activity and worth learning how to do, but also can take some time, particularly if you have a project with a lot of different resistors to sort out. Digital multimeters have the ability to measure resistance and some digital multimeters are “automatic ranging” this type are particularly useful as you can connect the probes to either end of a resistor of any value and it will range in to give you the correct value. Non auto range DMM have separate settings you have to switch too for each range of resistance value so often you need to roughly know if the resistance is just a few ohms or a few million ohms. Auto ranging DMM are now very common and available at the budget end of multimeters so if it’s your first meter be sure to look for that feature.

Another very useful feature on most multimeters is continuity checking. When selected this feature means that the unit will bleep whenever there is a connection between the probes, which you can check by simply touching the metal probe tips together. Continuity checking is super useful for a variety of reasons. An obvious use is you can check the wires that you are using in your project to make sure that they aren’t broken inside the insulation. You can also work out what things are connected, for example when using a PP3 battery clip it can be hard to see which battery connector connects to positive and negative, using the continuity checker you can see which is connected to which. Another great use for continuity checking is checking close solder joints that shouldn’t be connected. Sometimes it’s easy to create a tiny solder “bridge” between two solder pads that shouldn’t be there, checking that pads aren’t connected and don’t make the bleep is an incredibly useful trick.

Finally you can swap the probes into other sockets which enable the multimeter to read the current usage of a circuit. In this mode you make the DMM become part of the circuit making a connection so that the DMM has the current flowing through it as if the DMM and it’s probes are a single piece of wire. Setting the DMM to current mode the DMM measures and displays the current use on the screen. You need to be careful with this mode that you don’t accidentally connect the DMM up in a way that can create a short circuit and remember to change the probes before you measure any voltage as that can produce a short.

As a safety feature most DMM are fitted with fuses in case of a short and whilst many multimeter are rated for mains electricity work we would recommend only ever using a multimeter in battery and low power projects.