Multimeters are an incredibly useful tool for electronics and anything
if you're doing stuff around the house, you just need to know how to use them.
They are very useful but you can also hurt yourself or kill yourself.
We're gonna go over really quick on how to use it properly,
what to look for and how not to kill yourself.
First things first, I have here a desktop multi-meter or multimeter.
I'm more comfortable with multimeter but you'll hear both ways.
And then I also have this one that I use all around the house
and whenever I'm doing an electrical project because it's just very easy.
Now both of these can do different things - I mean, they obviously have
their pros and their cons but for right now we're gonna focus
on their most basic features and just not really worry about it too much.
The three things that we'd like to talk about today are:
checking the resistance, checking the voltage and checking the current.
One thing that I use for electronics specifically quite a bit is, I'm color blind
and I also am terrible at memorizing the color code stuff on resistors.
So if I have a resistor just laying there, I don't do well with saying,
"Okay, that is... yeah, I literally have no idea what colors those are."
But I do have a multimeter and I can just use it touch both ends.
It says 90k but I'm also touching it so I'm throwing things off.
So now it's saying exactly 100 kilo ohms.
The way I have this if I turned it on obviously and then I have
what looks like a horseshoe, the ohm symbol, right there.
With that you can just go and you can check anything rather easily.
And right there, 100 kilo ohms.
I can do the same thing with this and I will see 100.079
So, this is actually 100,000.080 ohms.
So this one being a more expensive even better, more precise multimeter
it can show that it's not exactly 100 kilo ohms but it's actually 80 ohms over.
Which this is a 5% resistor, so we're expecting some variation.
That actually shows a really good thing that you do need to think about
when you are doing testing because even though we like to think of ourselves
as not causing any sort of change in resistance, me, just touching the
two leads with the resistance in my body, it changes.
So you can see it's down to 98, 97 and again I did the same thing.
Now even just putting both of them together, it causes all sorts of confusion.
Remember that the multimeter and your body will change things so keep that in mind.
Resistance is very useful but is only useful with resistor.
This does not work with capacitors, does not work with inductors,
also doesn't work with powered circuits.
You only want things that are unpowered and isolated.
That doesn't necessarily mean that you can't use it on your circuitboards
even when things are going all around. It might be helpful to say,
"What's going on here? I want to check my resistance from one point to another."
And you'll notice that there are some parasitics that you didn't plan for.
You can use this with any part that is in a circuit but just know that
it's gonna be confusing and that doesn't necessarily mean the part
you are measuring has that resistance.
Since it's a multimeter and it does lots of things, we can also check the voltage.
Now, this is where things get tricky.
If you notice, there's four holes down here and it says 10 amp, microamp,
milliamp, common and then voltage. So, when I'm checking voltage,
I need to make sure I'm in this (port) because when you're checking voltage,
you want a very high impedance. You want your multimeter to be very
high impedance so that you don't have current flowing through it.
If I were to be plugged into the amp (port) right now and I were to go over this
let me power up this circuit really quick. Okay, so I just put six volts over this resistor.
Now, with my multimeter in voltage mode, I go and make sure not to touch it
so I don't throw it off and I'm measuring 5.93 volts, which makes sense.
Now, the way this works is when it's measuring voltage, the impedance that
the circuit sees from this is almost infinity that is close to possible
obviously it's not which is where you get some weird variations.
But you want your impedance to be nearly infinity.
However, as soon as you put this over to the microamp/milliamperes
or the 10 amp area, it drops its internal impedance to almost zero.
So if I had this lead connected in here and then did this same thing,
I would blow the fuse. At best, might melt some leads.
And this is actually why they tell you to never put these into an electrical outlet
because if you don't know what you're doing and you're plugged into the amp (port),
you will melt these and you'll blow the fuse and you might cause a fire.
My older brother did that when I was a kid and it scared the pants off of me
and it took me a long time to be okay with it.
Okay, when I'm properly set up, I can put this in the electrical outlet
to make sure that I have power or don't have power.
But if you are not certain and you're not confident, don't do it.
But if you take your time and think, you double check everything, "Okay, I can do this."
You can plug these into the electrical outlet and see exactly what voltage you get.
Right now I'm actually set up for DC so you wouldn't see anything
because your electrical outlet is AC but that's neither here nor there.
I'm actually going to change this really quick and show you how we would measure current.
Right now, as you saw, I measured the voltage across the resistor and now
we are going to figure out how to measure the current through the resistor.
That i'm going to set that up really quick.
So I just set it up so now we are going to measure current knowing that
I'm giving it 6V and that this is a 100 kilo ohm resistor.
I was anticipating it to be about 60 μA so that's why I put this in the μA area
and that gives it so we can see down there. Now, if we went in the 10 amp,
it just changes the range and you probably wouldn't have seen anything.
But if you do a couple of amps through this, again, you might blow the fuse
because it's not set up to measure large currents.
You always want to calculate it beforehand, before you plug things in
to know what you're expecting to read.
Now I have it set up so it comes from the power supply, goes through
the positive lead, through the multimeter, and again we're expecting
the impedance of the multimeter to be about zero then it's gonna
come out the negative lead and I'm going to touch it to this side
of the resistor and it'll go through the resistor and then back to the power supply.
Again, instead of being in parallel with the power supply to measure for voltage,
we need to be in series to measure for current.
I'm just gonna go and touch this and you can see 59.4 μA, so very close
to what we are anticipating and actually seeing this how we measure
just shy of 6V that's spot-on. So, exactly what we were expecting.
And that's it!
Really, that's all you need to know to measure resistance and voltage.
Again make sure with voltage, you have it set up right and even more importantly,
when you're measuring current, don't put it into the electrical outlet.
I never store my multimeter with it plugged in this just in case
I'm not paying attention next time.
Right now i'll just say, "Alright, I'm done with this. I'm gonna power this down.
I'm gonna pull this out and put it over here so I have high impedance
Just in case next time, when I come to use this multimeter,
I don't kill myself or melt things, cause a fire."
I hope that was helpful and also interesting.
If you have any questions or comments, leave it in the section below.
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