When repairing or troubleshooting a circuit, a multimeter is your best friend.
"How's it going, buddy?"
A multimeter is like a stethoscope for electronics.
It takes abstract concepts such as voltage and current and makes them real by giving
us the ability to measure them.
This particular model is a "manual-range digital multimeter".
manual-range" meaning that I need to set the particular range of values I want to measure.
and "digital" as it uses a digital display to show readings.
Auto-range multimeters, like this one, allow you to simply set the type of measurement
you want to make without the need to specify a value range.
Analog meters don't have a digital display, instead they use an old-fashioned mechanical
needle to show values.
Like this one?
Indeed, Ladyada - that is a rather *large* analog multimeter.
When is that from?
This one was made in the 1960s but multimeters were first made in the 1820s.
But not much has changed since then.
There's still a large display up top, a mechanical dial to select modes, and two wire leads to
connect your circuit.
So do people even use analog meters anymore?
Absolutely!
I really like analog multimeters because the moving dial makes it easier to see patterns
in your circuit-- easier than on a digital multimeter.
The simplest way to use a multimeter is for testing continuity, whether 2 points are electrically
connected to one another.
This is incredibly useful when checking for solder bridges and other shorts within a circuit.
Connect one test lead to the common ground terminal and another to the terminal on the
right.
Then connect the leads to each point in the circuit we want to test for continuity.
If the multimeter detects conductivity between those two points it will produce an audible
beep.
If the points are *not* electrically connected, no beeping shall occur.
No beeping.
Here's my Ladyada tip for using continuity mode in a multimeter.
In a loud office you can't hear the beeping, cradle it against your ear and that way when
you do continuity tests, you'll hear it nice and loud.
Nice!
To measure the amount of resistance between two points, set the dial to the lowest resistance
setting and connect the test leads to each test point.
If the multimeter simply displays the numeral "1" and a decimal point, that tells us the
that the resistance we're trying to measure is beyond the range of our current setting.
Keep increasing the range setting until the meter displays multiple digits appear.
This number is our resistance reading within the current range.
The dial is currently set to a "KΩ" or thousands of ohms range, so we have a resistance of
9.88 thousand ohms.
You may find yourself needing to measure the resistance of a very small component like
this surface mount resistor, and these multimeter probes are way too big.
In that case we suggest smart tweezers.
Smart tweezers are basically a small digital multimeter, except instead of wire probes,
there are two pointy tips.
Grab the component with the tweezer tips, then you can read the value off of the LCD.
Testing voltage is similar to testing resistance, but first we need to set the meter's dial
to either a DC or AC voltage range.
Here, we're testing a battery so we'll use the DC ranges.
Since I know this battery is supposed to provide 9 volts, I'll choose the lowest range that
has a maximum value above 9 volts - so 20V, in this case.
It appears this 9 volt is not living up to its name and with a reading of around 4.29
volts.
Sorry buddy, you don't have to go home, but you can't provide current here.
Don't forget, if you want to measure voltage inside of a circuit, it has to be plugged
in and powered.
If I have to measure a lot of voltages in a circuit, I like to use a probe multimeter.
After you connect the ground contact, you can probe any voltage you want, and see the
result on the LCD.
Measuring current can be a little trickier than measuring voltage or resistance because
we need to send the electrical signal through our multimeter and it can only handle up to
a certain amount of electrical current before blowing one of its internal fuses.
The terminal on the right can handle up to a maximum of 200mA, while the terminal on
the left can handle up to 10A, but it won't detect relatively small amounts of current.
If you're unsure of the maximum amount of current you'll be measuring (but you know
it's below 10A) start with the higher rated terminal on the left & set the dial to the
highest Amperage range.
Route electricity through the multimeter by creating a break in the test circuit and connecting
the test leads across the break.
If the multimeter displays a reading of zero Amps, we can safely switch over to using the
lower rated terminal and the next-lowest range.
Keep decreasing the range until you see a reading of multiple digits.
So we can see now our circuit is using 15mA of current - and our multimeter's fuses are
safe & sound.
It's pretty common to blow the fuse on your multimeter when testing current.
But luckily, it's really easy to replace.
Start by turning off the multimeter, and removing the leads.
Unscrew any screws in the back, and open up the battery case.
There might be some more screws you have undo, then turn it over and remove the body from
the plastic casing.
You'll be able to see the two replaceable fuses inside.
Check which one's blown and go to your local hardware store for a replacement.
Those are the essential basics you can test with a multimeter - but many meters also have
additional features such as the ability to test capacitance, frequency, and temperature.
Still others have evolved to be quite small and portable.
Now, if you'll excuse me, I'm off to do a bit of testing.