You might be asking, "What is continuity?" But don't worry, it's quite simple! Continuity means, are two things electrically connected. So if two electronic parts are connected with a wire, they are continuous. If they are connected with cotton string, they are not: while they are connected, the cotton string is not conductive.
You can always use a resistance-tester (ohmmeter) to figure out if something is connected because the resistance of wires is very small, less than 100 ohms, usually. However, continuity testers usually have a piezo buzzer which beeps. This makes them very useful when you want to poke at a circuit and need to focus on where the probes are instead of staring at the meter display.
For some basic circuits you can just look to see where the wires go to determine continuity but it's always wise to use a multimeter. Sometimes wires break or you're tired and can't easily follow all the PCB traces. I use continuity check all the time!
Continuity is one of the most important tests. Here are some things it is good for
- Determine if your soldering is good. If your solder joint it is a cold solder connection it will appear connected but in actually it is not! This can be really frustrating if you are not experienced in visually detecting cold solder joints
- Determine if a wire is broken in the middle. Power cords and headphone cables are notorious for breaking inside the shielding, it appears as if the cable is fine but inside the wires have been bent so much they eventually broke.
- Making sure something isn't connected. Sometimes a solder joint will short two connections. Or maybe your PCB has mistakes on it and some traces were shorted by accident.
- Reverse-engineering or verifying a design back to a schematic
You can only test continuity when the device you're testing is not powered. Continuity works by poking a little voltage into the circuit and seeing how much current flows, its perfectly safe for your device but if its powered there is already voltage in the circuit, and you will get incorrect readings
Always test to make sure your meter is working before starting the test by brushing the two tips together, and verifying you hear the beep. Maybe the battery is low or its not in the right mode.
Continuity is non-directional, you can switch probes and it will be the same.
If you are testing two points in a circuit and there is a (big) capacitor between those points you may hear a quick beep and then quiet. That's because the voltage the meter is applying to the circuit is charging up the capacitor and during that time the meter 'thinks' its continuous (essentially)
Small resistors (under 100 ohms or so) and also all inductors will seem like short circuits to a multimeter because they are very much like wires.
Likewise, continuity doesn't mean "short" it just means very very low resistance. For example, if you have a circuit that draws an Amp from a 5V supply, it will appear to be a 5Ω resistor. If you measure that with your meter it will think its a short circuit, but really its just a high-drain circuit.
First step is to get your multimeter into the correct mode. Look for the icon that looks sort of like a 'sound wave'
Here are three examples. Note that sometimes the mode is "dual" (or possibly more) usage,
For a majority of multimeters, you're ready to go, just touch the tips of the probes together so that they make a beeping sound!
Here's a video demonstration: