This is the second part of my oscilloscope tutorial showing you how to measure things with
an oscilloscope.
The first thing you are going to have to use is your oscilloscope probe.
You should have got one with your oscilloscope, but if you didn't, you can get one for $10
from www.mpja.com
All oscilloscope probes will have a little attenuation switch which can be set to
"X1" or "X10" attenuation.
Most of the time you should leave it set to "X1".
The "X10" setting divides the signal by ten which you usually don't want unless
you're working with higher voltages.
The oscilloscope probe will have a "BNC" plug on the back that you plug into the oscilloscope
like this.
Once that is done you don't need to unplug it again.
The probe will have two main parts: The ground clip and the tip.
The ground clip is just a little alligator clip that you should attach to
the circuit ground or circuit common.
If you don't know what that means just connect the ground clip to the negative terminal of
your battery.
Now the other important part is the probe's tip.
When you want to measure the voltage in the circuit you touch the tip of the
probe to the part of the circuit you want to measure.
You can also use these probe clips to grab wires in the circuit,
leaving your hands free to do other things.
Now I'm going to connect my probe to a signal generator so I can show you some
easy examples.
So now that you have your probe clipped on to a part of your circuit you should
see some sort of signal on the screen. Let me explain what you are seeing.
The screen is evenly divided up into little squares or "divisions".
Each division represents a certain number of volts on the vertical axis.
On the horizontal axis each division represents a certain number of
milliseconds or microseconds.
Right now I have it set up to be one volt per division
and one second per division for the sake of simplicity.
As you can see it's not so easy to see what's happening in the signal.
So we want to sort of zoom in and out.
We do this by changing the volts per division and the seconds per division.
The exact setting you will use will depend on the signal you are viewing
and your personal preferences.
And there's no harm with changing these settings so you can zoom in out all you want
until you get a good sense of what is happening.
Also, you can use these little positioning knobs to move the waveform up and down
so it fits nicely on your screen.
The next thing I want to talk about is DC coupling, AC coupling and ground coupling.
All oscilloscopes will allow you to choose between these modes.
DC coupling is usually what you want to use for most circuits because it will
allow you to view most DC voltages.
For example here I'm going to connect my probe to a nine volt battery.
You can see how the line jumped up to show the presence of the DC voltage.
If you count the number of vertical divisions we can see that the voltage being shown
is roughly nine volts.
Also since I have a digital oscilloscope I can see that it is doing the measurement for me.
However sometimes you might want to ignore the DC component of a signal
and only focus on the small AC variations.
An example of this is if you're trying to discover if your circuit has
a properly filtered power supply.
So let's look at my simulated example.
Over here you can see a power supply that looks like it is 5 volts.
But if I set my oscilloscope to AC coupling
and zoom in I can see that in fact there are some tiny AC voltage variations on
top of the DC signal.
According to the display each division is representing one hundred millivolts.
So the AC ripple of the signal is approximately one hundred millivolts
from peak to peak.
Now one hundred millivolts is fine - that is only two percent of the DC voltage of five volts.
But if you ever run into a DC power supply with many volts AC on it you know
that something is broken and you must fix it.
Now remember the final type of coupling I talked about - ground coupling?
That basically means that you are not measuring anything at all.
You are just measuring ground.
In other words it's kind of a useless setting and the only time you ever use
it is when you want to reposition your waveform
to represent zero volts in the middle of the screen.
Finally I want to show you a real-world example on this headphone amplifier I built.
You can see that when I crank up the volume volume I get massive fluctuations
in the power supply voltages.
So what's the solution?
I have to add some capacitors to smooth out the voltage.
Now here is what it looks like after the capacitors are installed. Much better.
And the sound will be better too.
So that's ninety nine percent of what you will ever need to know about oscilloscopes!
Now if you want to become an expert, check out the next video where I will talk about
the advanced functions in oscilloscopes.