What is a multimeter?

- When working with electronics, a multimeter is the go-to tool for testing and troubleshooting circuits. It's your first line of defense for tracking down problems. A multimeter is a single device that can measure a variety of electrical quantities and most modern multimeters have a numeric display like this one so they're called digital multimeters or DMM. You can buy a DMM at most hardware or electronic stores or from an online retailer like SparkFun or amazon.com. And there's a wide range of multimeters available from different manufacturers that vary in capabilities. When choosing a DMM, at the very least, make sure it can measure voltage, current, resistance and electrical continuity. This is a basic DMM, which only measures those four necessities. I bought it from SparkFun.com, which sells it as a low-cost entry-level model. So if you're a beginner hobbyist on a budget, then a DMM like this one should serve you well. If you want to get something with a bit more capability, I would recommend a DMM like this Extech MN36, which I borrowed from my wife. In addition to the four basic DMM measurements, it can also measure capacitance, frequency and temperature, plus it has the nice ability to automatically set the range for measurements so you don't have to. I've included a document called DMM List.pdf, which includes information about both of these DMMs in the exercise file for this video. You should choose a DMM based on your budget and needs. I'll be using the DMM from SparkFun because it's adequate for what I need to measure throughout this course. There are three main parts to this DMM. At the top is the display where I'll read the value from a measurement. Below that is the selector knob, which I'll use to choose the type of measurement I want to measure: Voltage, current, resistance or continuity. And when I'm not using the DMM, I always keep this knob in the off position to save on the battery. At the bottom of the DMM are three ports that I'll use to connect my probe. These are basic needle test probes, which are typically colored red and black. There's no difference between the probes, other than their color but the black probe is conventionally attached to common ground or negative reference within a circuit and then the red probe is used to check voltages at other points throughout the circuit. The probes for this multimeter use a type of connector called a banana connector because the plug supposedly looks kind of like a banana. This type of connector is common amongst multimeters and allows you to attach a variety of different types of probes. Now, I have two probes but there are three ports on the DMM. So which port should I connect each probe to? The black probe is the simplest. Since I'll usually be connecting it to the common ground for voltage measurements, I'll attach the black cable to the port labeled com, which stand for common. This leaves me with two options for the red probe and I almost always use the port on the right for milliamps, volts and ohms. I'll connect the probe to this port for all the resistance and voltage measurements and for smaller current measurements that are less than 200 milliamps. This other port is specifically designed to measure larger currents up to 10 amps. I rarely ever use that port and for this course, I'll only be making measurements that require the red probe to be connected to the right side.