This blog post on using a multimeter is an excerpt from Lesson D-2 of our Intro to Robotics program. Intro to Robotics consists of four levels that start at the beginning and systematically teach you to build circuits, use a Raspberry Pi, and write code in Python. In the final level, you will take all the skills you've learned and build a mobile robot of your own. The full Intro to Robotics course contains 72 detailed lessons including 225+ videos and 200+ projects and activities. Sample lessons and full scope and sequences for all four levels can be found here.
A multimeter is a tool used throughout electronics for measuring voltage, current, and resistance. Some multimeters may also have additional specialized functions like testing diodes, transistors, or other electronic components. You may see multimeters referred to as voltmeters, but this is a legacy name that started back when some devices only measured voltage. The terms ‘voltmeter’ and ‘multimeter’ are often used interchangeably, but ‘multimeter’ is the more popular term for devices that have multiple measurement functions available.
Multimeter Functions
Our Intro to Robotics Level D kit contains a multimeter with the following functions:
- Voltage measurement -- both DC and AC
- Resistance measurement
- Current measurement
- Diode check
- Transistor check
Multimeter Hardware
A multimeter has a rotating selector switch that’s used to turn the multimeter on and off as well as select the type of signal that will be measured.
The multimeter runs on an internal 9-volt battery so it’s important to make sure the multimeter is turned off when not in use to avoid unnecessarily draining the battery.
The multimeter has removable leads, also known as probes, that are used to touch areas of a circuit or components for measurement. These leads have handles with pointed tips to aid in touching only the specific component that you intend to measure.
You may notice there are three jacks for leads and only two leads. This is because the red lead will be connected to one of two jacks when making different measurements.
The measurement taken will be displayed on the small LCD screen above the selector switch. Since there are a limited number of digits available on the display, the range selection will determine how accurately those digits are used.
Measuring Voltage
Measuring voltage can be very useful when building projects. You may want to do things like measure the voltage level of a battery or determine if proper voltage is getting to a sensor on your robot. With a multimeter you can measure the exact voltage that is present at any point in your project.
Measuring Resistance
Measuring resistance will come in handy when checking to see if two components are connected or if you can’t remember the resistor color codes. The main thing to remember about measuring resistance is that the component cannot be powered on. The multimeter will run a tiny amount of current through the component in order to measure its resistance, and this measurement will be thrown off if there is additional current flowing through the component from the circuit. Your multimeter can also be damaged if there is enough current coming from the circuit, so always make sure components to be measured are disconnected from the circuit or the entire circuit is powered off before making resistance measurements.
A term you might see related to resistance is called continuity. When something has very low resistance between two points it is said to have continuity. This might apply to a single jumper wire or multiple connections made through wires and your breadboard.
In the image above, a multimeter is being used to measure the resistance between two pints on the breadboard that are connected by multiple jumper wires. With only 5.1 ohms of resistance present, these two points would be considered to have continuity.
You may see references later in this course to “checking the continuity” of component or connection. This just means using your multimeter to verify there is very low resistance between the points to be checked, which means you have verified there is a good electrical connection between these points. If higher than expected resistance or a complete open is measured, then you have located a problem that will need to be resolved before continuing.
Measuring Current
Current measurements can be used to determine how much current is flowing through a specific point in a circuit. Measuring current is different than voltage or resistance in that to measure current you must break the circuit at the point you wish to measure and use your multimeter to complete that portion of the circuit.
The amount of current you plan to measure will determine which location you will use for the red lead connection to your multimeter. In order to measure current, you must first determine how much current you plan to measure and set the range selection and red lead position appropriately.
After the proper range and red lead position have been selected you must power the circuit down and break the circuit at the point you would like to measure. Next, complete the circuit using the leads of your multimeter making sure to keep the black lead toward ground or negative of the battery. Reversing the leads won’t damage anything but your current reading will indicate a negative current value which might be a little confusing.
When the circuit is powered back on, current will flow through the multimeter and the amount of current measured will be displayed on the screen. If there are components like switches or LEDs in the circuit that might affect the current at your measurement point, then you can try switching those components on and off to watch how they change your current measurement in real-time.
When you’re done measuring the current, power the circuit down, and remove your multimeter from the circuit. Make sure to complete the circuit in the location you were measuring so it will operate properly with your multimeter removed from the circuit.
This blog post on using a multimeter is an excerpt from Lesson D-2 of our Intro to Robotics program. Intro to Robotics consists of four levels that start at the beginning and systematically teach you to build circuits, use a Raspberry Pi, and write code in Python. In the final level, you will take all the skills you've learned and build a mobile robot of your own. The full Intro to Robotics course contains 72 detailed lessons including 225+ videos and 200+ projects and activities. Sample lessons and full scope and sequences for all four levels can be found here.