Whether it’s your smartphone, your computer, your speakers or the ordinary light bulb, every electrical device needs a specific amount of electricity to function. This electricity must be regulated to ensure the proper functioning of your device. Too much and the device fails; too little and it may not work at all.
A multimeter is a tool used to measure the amount of electricity flowing through a certain component by measuring current (amps), electrical pressure (voltage), resistance (ohms), and continuity.
If you are interested in checking, troubleshooting, or designing your DIY electronics/electrical projects, a multimeter is an essential tool you must have.
Getting to know the multimeter
Before you measure anything with the device, you should first familiarize yourself with the common parts and features of a multimeter.
Display/Scale: A display or scale is where you will see the values of your measurements.
Rotary switch: The rotary switch allows the user to switch between the types of measurements they are trying to test. This would include valuable measurements such as voltage, resistance, and current.
Function button: Some values provided by the rotary switch will have more than one function. Use the function button to switch between these functions.
Input jacks: The input jacks are where you will insert your test probes. Most multimeters will have three input jacks. Multimeters usually come with two test probes. The black test probe will always be inserted into the COM (common) input jack. Unless you are trying to measure current measurable by more than one amp, your red test probe should always be inserted into the rightmost input jack where it can measure voltage, resistance, continuity and currents measurable in milliamps.
Learn through the hands-on application of a multimeter
The best way to learn is to apply. Today you are going to learn how to use a multimeter by measuring the values of this DIY backup modem power supply.
The goal is simple. Take a 20 volt power tool battery and reduce its voltage to meet the power requirements of a 12 volt modem. This project will use a buck converter (buck converter), a diode, some wires, and of course the multimeter.
For those wondering, a buck converter (the circuit with a red LED in the picture) is used to adjust and step down the voltage of a power source. The one in the picture is prebuilt; you can easily buy one at any electronics store!
How to use a voltmeter
Voltage is one of the most common measurements you will need to measure. Voltage is the difference in electrical potential between two points. Much like water pressure from your garden hose, voltage is the electrical pressure that pushes current through the circuit.
Let us measure the voltage by first checking if your test probes are in the default setting. The black test probe should be inserted into the COM port and the red test probe into the rightmost port. Use the rotary switch until it lines up with the V (voltage) symbol.
If you are measuring a battery-powered device/circuit, make sure the display shows the DC symbol. If you are testing something that is not battery powered, such as household appliances (refrigerator, washing machine, electric fan), press the function button until the screen says ready to read alternating current.
Our project is powered by a power tool battery, which means we use DC values from our multimeter. To measure the voltage coming out of the buck converter, touch your black test probe to the negative (-) output and the red test probe to the positive (+) output of the buck converter circuit.
Great! Looks like the down converter is producing exactly the 12 volts our 12 volt modem needs. This means that the down converter does not need to be adjusted.
Batteries are another item commonly measured by voltage. The image below shows an 18650 battery providing approximately four volts. If the voltage shows a negative sign, it simply means that your test probes should be reversed.
How to measure current
Current is the flow of electrons from one point to another. As we discussed earlier, if voltage is the water pressure of your garden hose, current is the water itself being forced out of the hose.
To measure current you will need a live/powered circuit. Current measurement can be a little tricky because you have to build your multimeter into the circuit itself. You will therefore need to insert your test probes in such a way as to achieve this.
Let’s see how much current our device consumes. Set your rotary switch to measure “mA” (milliamps). If you’re not sure, better insert your red test probe into the multimeter’s “10A” input jack and set your rotary switch to measure “A” (Amps) just to be sure. If your reading doesn’t register even a full amp, place your red test probe back into the default input jack and set your rotary switch to measure milliamps.
As you can see, the wire has been disconnected from the buck converter, making our multimeter part of the circuit. The display provides a small value of 1.07 milliamps, as one would expect since the device is not in use. Once your device is used, expect the values to increase.
How to use an ohmmeter
Resistance is measured in ohms, hence the name ohmmeter tester. Resistance is a property of a material that makes it more difficult for current to flow. It’s like when your garden hose gets clogged with dirt, making it harder for water to drain.
All materials have some level of resistance to electricity. Rubber has high strength, which is why it is used to insulate wires. Copper has very little resistance, and that is why copper wires are used to transfer electricity.
The DIY emergency modem power supply uses a diode as reverse polarity protection. A diode is like a check valve: it lets current flow in one direction and blocks current if it tries to flow in the opposite direction.
The markings on the diode are indistinguishable. The ohmmeter can tell if the diode is correctly oriented.
Set the rotary switch to the Ω (omega) symbol, which stands for ohms, then use the test leads to see if it measures resistance.
The ohmmeter reads zero. This means that this diode orientation provides zero resistance when current flows from the wire that the black test probe is touching.
If the test probes are reversed, the ohmmeter reads approximately 2.4 megohms (note the M symbol on the display). This means that this orientation will prevent (resist) current from flowing through the circuit.
Aside from diodes, one of the most common things to measure with an ohmmeter will of course be resistance. Unlike a diode, a resistor will block (resist) current for whatever orientation you are using your test probe in. In the image below, the resistor has a resistance of 465 ohms.
How to check continuity
Continuity isn’t really a value of any kind. However, it is still a valuable test function of a multimeter. The continuity function will test if the current flow of a device/circuit is disturbed. One of the most common uses of the continuity function is to check whether two points in a circuit are connected or not.
To do this, set your rotary switch to the wave/diode symbol, as circled in the image below.
Press the function button until the wave/diode symbol appears on the screen. If you touch two points of a circuit (node) and it emits a sound, it means that they are connected. If the multimeter does not make noise, the points are not connected and you have an open circuit.
As you can see in the image above, one of the down converter wires is not connected. The multimeter does not make noise.
The wire is now connected. The multimeter emits a sound indicating that the two points are connected.
Another common use of the continuity function is to check if a fuse has blown (resulting in an open circuit) or is still in working order.
For those looking for a new multimeter
Multimeters come in different shapes, sizes, and configurations. Some have additional features that make the multimeter more capable. As a beginner, you’d want a multimeter that can measure voltage, amps, ohms, continuity, and features that make it easy for you to read those measurements.
It is highly recommended that you choose a multimeter with a digital display, true RMS, and autoranging functionality to make your testing easier.
Want to start using a multimeter to take electrical measurements? This guide is for you.
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