How to Use (and Choose) a Multimeter!

Checking your car battery life, debugging circuits, and finding that pesky short are all super useful functions that can be performed with just one awesome tool: the multimeter!

First of all, what the heck is a multimeter??   Excellent setup question! It’s a handheld device with bunch of different electrical meters — hence, multi-meter!

Measuring voltage, current, resistance, and continuity (aka electrical connection) are the most common uses of a multimeter.  Read on to learn what this means, how to do it yourself, and how to choose your very own multimeter!

Choosing a Multimeter!


There are a few key differences between multimeters, the main one being analog versus digital:
Analog multimeters show real-time changes in voltage and current, but can be difficult to read and log data.

Digital Multimeters are easier to read, but may take some time to stabilize.

There are also auto-ranging multimeters, that automatically detect the measurement range, and manual ranging multimeters where you have to choose a range yourself (or start with the highest setting and work down).

Other than those two main differences, you’ll want a multimeter that has separate ports for current and voltage measurements (this is a safety issue, both for the meter and for yourself).

Next comes the fun part: features! Multimeters all have voltage and current meters (otherwise they’d just be called voltmeters and ammeters!), and most can also measure resistance. There are a variety of other “extra” features depending on manufacturer and cost (e.g. continuity, capacitance, frequency, etc.).

Second-to-lastly, there are a ton of different types of probe leads, including alligator clips, IC hooks, and test probes. Can’t decide? Here’s a kit that has four different types!

Lastly, always check the multimeter maximum voltage and current ratings to be sure that it can handle what you want to use it for.

Using a Multimeter!

But first! A quick overview of voltage, current and resistance!

My favorite analogy for electricity is the “water flowing through a pipe” analogy. In this analogy, voltage is similar to the water pressure, current is like the water flow (except with current you have electrons instead of water molecules!), and resistance is akin to the size of the pipe. Check out this tutorial for an awesome and thorough overview of electricity.

Keeping these analogies in mind helps us to figure out how, and what, we are measuring.

Measuring Voltage:

A voltage measurement tells us the electrical potential, or pressure, across a particular component.

Voltage is basically the “oomph” in our circuit, s so we want to avoid drawing any power from the circuit when we take a voltage measurement. This means we need to measure voltage in parallel with a particular component using infinite (or really, really high) resistance to prevent any electrical current from flowing into the meter.

Using a multimeter to measure voltage across a component (or battery!):

1. The black multimeter probe goes into the COM port, and the red probe into the port marked with a “V”.

2. Switch the dial to the “voltage” setting (choose the highest setting if you have a manual ranging multimeter).

3. Place black probe on negative side of the component, and red probe on positive side (across, or in parallel with the component). If you get a negative reading, switch the leads (or just note the magnitude of the voltage reading).

Read the meter output and you’re done! Not too bad 🙂

Measuring Current:

Taking a current measurement tells us the amount of electricity flowing through a given component or part of a circuit.

To measure current, we need to measure all of the flow in our circuit without consuming any power from the circuit and reducing the current measurement. This means we measure current in series with a component and we want our meter to have zero resistance.

Using a multimeter to measure current through a component:

1. The black multimeter probe goes into the COM port, and the red probe into the port marked with an “I” or an “A” (or “Amp”).

2. Switch dial to the current setting (choose highest setting if you have a manual ranging multimeter).

3. Connect red probe to current source, and black probe to the input of the component, so that the current flows from the source, through the meter, to the component (in series with the component).

Read the meter output! If you’re not getting a reading, switch to a lower setting.

Measuring Resistance: 

Measuring resistance is pretty straightforward, but you do have to disconnect individual components from a circuit to get their actual resistance, otherwise the rest of the components in the circuit can interfere with your measurement.

Using the multimeter to measure resistance of a component:

1. Put the black probe in COM port, and red probe in the port marked with a “Ω” or “Ohm” — it should be the same port as the voltage port.

2.  Switch dial to setting marked with a “Ω” (may have to choose approximate range for manual ranging multimeter).

3. Place probes on either side of the component (orientation doesn’t matter).

Read the meter output and you have conquered resistance!

Bonus: Measure Continuity!

The continuity measurement checks if two points in a circuit are electrically connected, otherwise known as a conductance test. Before measuring continuity, be sure that the circuit power is OFF.

Using the multimeter to measure continuity: 

1. Place black probe in COM port, and red probe in voltage port.

2. Switch dial to setting marked with an audio symbol.

3. Place probes at points you want to check — if the meter makes a beep sound, it means the two points are connected.

Le fin!

Go forth and measure all the things!

Now that we know how to use a multimeter, get crackin’ on all those at home, DIY projects! To get you started, here are a few quick, practical, & fun projects:

1. Measure the resistance of your skin! Change the distance of the probe leads and see how resistance changes. Lick your fingers (or dip them in water) to see how moisture affects resistance!

2. Measure the voltage across AA, 9V, or other batteries around the house/workplace/school to locate dead, or dying, ones.

3. Make a lemon battery and measure the voltage and current output.

4. Use the continuity setting to check if different materials conduct electricity.

 

Looking for more info on multimeters?

Check out this in-depth guide by the folks at Tools Critic!

Using an Oscilloscope!

Visualize all those mysterious electronic signals with an oscilloscope!

Learn how to build and use a super simple $30 oscilloscope perfect for electronics hobbyist applications. It’s also a great way to get started using some of the fancier oscilloscopes!

Reading and Changing the Oscilloscope Display

Every oscilloscope has a window that displays the voltage output of your signal. On every display, the y-axis is voltage, and the x-axis is time.

You can zoom in and out of the display grid by adjusting the “Volts per division”* or “Seconds per division”.

On this oscilloscope, the voltage adjustment switches are on the left side (bottom two switches), and they let you zoom out to as much as 5 Volts (“V”) per division, and zoom in to 10 mV per division.

Adjust the time scale using the “+” and “-” buttons on the right side.**

*”Per division” means the size of the squares, e.g. 1V per division means that each square is 1V in height, 1 second per division means that each square is 1 second wide. 

** Be sure that the time scale is selected (will be highlighted with a box around it — this is the default selected setting, change settings using the “sel” button, described in more detail in the next section.

Other Basic Features 

This oscilloscope has all the expected features of larger, more expensive ‘scopes, and also is a great introduction to some of the more complex versions.

On the left side, the top switch allows you to choose between a ground signal, a DC signal, and an AC signal. On the right side of the oscilloscope are four buttons:

1. The “ok” button (very top button): Pushing it once takes a snapshot of the screen, which can be saved to the oscilloscope. Holding this button down displays key numeric values about your signal, like the maximum and minimum voltage, signal frequency, etc.

2. The “+” button: Similar to an up arrow key, pushing this button allows you to sort through options.

3. The “-” button: Same as the + button, but, you know, scrolls down

4. The “Sel” button: Pushing this button allows you to select different features (described in order):

A. Change the time scale.

B. Set how the oscilloscope display refreshes – “Auto”, “Norm,” or “Sing”. More on these in the next section.

C. Set the trigger slope. More on this in the next section.

D. Change the trigger level. More on this in the next section.

E. Adjust the horizontal position of the oscilloscope display.

F. Change the vertical position of the display.

 

Oscilloscope Trigger

Oscilloscope triggers cause the oscilloscope to display a signal. Triggers are set at a specific value, or “trigger level,” along a specified direction, or “trigger slope” (more info below).

The trigger helps to display the exact electrical signal that you want, so that you get a stable display and measurement. In this ‘scope, the trigger is set on the right side of the display and the LED at the bottom flashes when the trigger is detected.

The simple oscilloscope in this tutorial has three trigger modes that you can switch between using the “+” and “-” buttons:

  1.  Automatic (“Auto”): Display continually refreshes, regardless if triggers are met.
  2.  Normal (“Norm”): Display only refreshes if the trigger is met.
  3.  Single (“Sing”): Same as normal mode, waveform display is held after a trigger has been detected.

More on Trigger Level and Trigger Slope!

The Trigger Level is a set, internal voltage that is compared to the signal, or input, voltage. The oscilloscope triggers when the signal voltage is equal to the trigger voltage. If an electronic signal rises and falls, then the trigger would happen twice: once when the signal is rising and again when the signal is falling. The trigger slope lets you choose which voltage (rising or falling) to trigger on.

 

Connecting a Component!

Now, to see the electrical signals at work in the world around you, connect the black lead to ground, and the red lead to the part of the circuit that you want to measure the voltage.

 

For example, if you want to measure the voltage output of a sensor, like the capacitor in the photo to the right, you want to connect the red probe after the sensor.

 

You may also want to calibrate your scope using the on-board signal. See the datasheet for more info.

 

Finally! Turning on the DSO138 Oscilloscope

The an oscilloscope kit in this tutorial takes about 2 -3 hours to assemble (instructions here), but is definitely worth it because many reasons! Here are a few: It’s a great way to learn circuit components, get familiar with schematics, and practice soldering (and de-soldering….). And, honestly, it’s pretty relaxing.

Once you’ve got the ‘scope assembled, it needs 9V and about 0.1A. There are two power ports: a barrel jack and a male JST connector. You can use a 9V battery with the barrel jack (OMG it’s portable!), or a power supply with the JST connector.

The exposed wire on the top of the oscilloscope is a square wave signal to help you calibrate the signal (see the datasheet for more info).

Be sure to use less than 12V or you risk heating up the board and possibly damaging it (don’t let the black smoke out!).

 

Plug and Play!

Now you know all the basics to connect your oscilloscope to sensors, your tongue, and other low power sources to watch the wonderful world of electricity at work!

Please leave a comment in the tutorial if you have any questions or would like more info about the oscilloscope kit. Now go forth and explore all that electricity! 😀

Interested in building a capacitive touch sensor like the one used in this tutorial? Check out this tutorial!