In this video I'm going to cover multimeters and how to use them to measure voltage, current
resistance and continuity.
First up where do you buy a multimeter?
Multimeters are everywhere. You can get them at radio shack, sears, dollar stores
wal-mart amazon ebay
whatever is easiest for you.
Okay so how do you choose which one to get?
First up at the bare minimum make sure the meter you're looking at can measure voltage,
current, resistance and continuity.
If you can find one that measures capacitance and temperatures as well
go for it.
Unless you're working with some super special application don't worry too much about accuracy.
+/- 2% is usually good enough
and even cheap multimeters these days will be that accurate or better.
Next the multimeter should have a digital display not that old school analog crap.
And it should have automatic ranging functionality for as many things as possible.
Trust me don't waste your time screwing around with manual ranging.
If you're too lazy to shop around just get this one. Fifty bucks, it'll do everything you
need and you won't outgrow it anytime soon.
Okay so now you have a multimeter - how do you use it?
Let's start with measuring DC voltages.
First check the cables.
Make sure the black lead is in the jack labeled COM or COMMON.
And once it's in there you'll never need to take it out because the black lead always
goes to COMMON.
The red probe on the other hand is something you'll have to pay very close attention to.
If you plug it into the wrong track you will blow a fuse in your multimeter.
We want to measure voltage right now so I'm plugging the red lead into the jack labeled Volts
not Amps.
Next, set the dial to measure DC voltage.
Touch the red probe to the positive terminal of your device and the black probe to the negative
terminal of your device and you should get a voltage reading.
If you get the wires backwards that's ok you'll just get a negative reading on your multimeter
and that's actually a good way to figure out polarity.
Now you can measure voltages in pretty much any DC circuit as long as you're careful
to not short anything out with the metal probes.
Okay let's move on to measuring AC voltages.
Set the dial to the AC voltage setting and again make sure the red lead is in the jack labeled Voltage.
Touch the probes to the AC voltage source that you want to measure and you'll
get your reading.
As long as you don't touch metal parts of the probe or short them out this is perfectly
safe.
And as you'd expect there's no AC voltage coming out of this DC battery.
Measuring resistance is easy too.
Make sure the red lead in the jack labeled ohms for resistance
and set the dial to the resistance setting.
Here is me measuring the resistance of the skin on my hand. Here is me measuring the resistance
of a resistor.
And here I am measuring the resistance of a speaker.
Now you might be wondering if you can measure the resistance of something in a circuit.
Well unfortunately it most likely won't work.
You're going to have to remove the resistor from circuit before measuring it.
Next let's talk about continuity.
Measuring continuity basically just means checking whether or not there's a good connection
between any two points in the circuit.
To measure continuity make sure your red probe is in the jack labeled continuity, (or in my case resistance)
and set the dial to the continuity setting.
Yest that the continuity function is working correctly by touching the probes together.
Whenever there is almost zero resistance between two points the multimeter will beep.
You can use the continuity function to check if cables are internally broken or not.
In the context of circuit boards, if there's a good copper trace between any two points
the multimeter will beep.
If the circuit board is messed up, no beeps for you!
Finally let's use our multimeter to measure current.
Set the dial to Amps setting.
For almost all multimeters there's going to be a separate jack just for measuring current.
My multimeter has two. One for currents up to 10 amps and one for currents up to 400 milliamps.
I usually start out with the Amps jack but if I need more accuracy I can switch to the
milliamps jack later.
Now measuring current is a little trickier than the rest of things.
I can't just touch the probes and get an Ampere reading.
In order to see how much current is flowing through a wire, I have to cut the wire, and splice in
the multimeter in series with the flow
before I can get a measurement.
Here I have a simple circuit with a battery pack, a motor and some wires. In order to
measure the current drawn by the motor, I cut the wire, splice in the multimeter,
and now I can see that the motor is drawing sixty milliamps.
If I want more accuracy I can switch the milliamp setting
and now I can see that the motor is drawing
somewhere between fifty seven and sixty three milliamps.
All right thanks for watching and have fun with your new multimeter!