Hey Guys!
It's Mike from The Geek Pub.
And in this vide we're going to talk about Oscilloscopes!
So let's start this tutorial with a little comparison.
You're probably alreadyl familiar with a multimeter, but let’s quickly review because I think
it will help you understand the oscilloscope a little better.
When measuring voltage, a multimeter takes a single “point in time” reading of a
circuit.
For example, when connected to this battery it shows 9v DC on the screen.
If we hook the multimeter to our mains power supply it will show somewhere around 120v
AC on the screen depending on where you live (or around 220v AC if you live in other countries).
Again, these are point in time readings.
And the truth is, if you measure AC voltage over time it's not outputting 120V at all!
This is where the oscilloscope comes in.
Oscilloscopes allow you to measure a circuit’s voltage over time, taking many thousands of
readings and plotting them on the screen over that time.
Many modern oscilloscopes can even write this output to a file for later in-depth review
on a PC or Mac.
You can see when I connect the oscilloscope to the 120V AC mains in my house, that the
voltage isn’t 120V after all.
It is constantly changing in this waveform pattern.
It’s constantly changing from -170V to +170V!
This is why it is called alternating current!
A multimeter will just show the average reading of this output in real-time, or more accurately
the Root Mean Square (or RMS) reading.
It takes an oscilloscope to see what’s actually happening!
Now let’s take a look at the oscilloscope’s display so that we can understand exactly
what is being represented.
The display is made up of a grid.
The size of this grid varies by oscilloscope brand and model, but they all work basically
the same.
The horizontal axis of this grid represents the time scale, while the vertical axis of
the grid represents the voltage reading
Each box in this grid is called a “division”.
These divisions are configurable with the knobs on the front of the oscilloscope, so
that they can represent larger or smaller scales.
By turning the horizontal control knob for example, we can make the divisions represent
a longer or shorter period of time.
Or by turning the vertical knob, we can make the divisions represent a smaller or larger
voltage scale.
This is in effect a zoom feature of the oscilloscope allowing you to zoom in and out of the signal
you are capturing.
It’s also handy for when a signal is simply too large to fit on the screen, you can zoom
out to see it.
Now let’s take a little deeper look at these waveforms.
If we look back at the signal from our standard 120V house mains, you can see it forms a nice
wave pattern.
This pattern is cycling at 60 times a second between -170 and +170 volts.
This type of waveform is called a sine wave.
Sine waves represent analog signals.
Let’s take this Arduino and connect one of its digital output pins to the oscilloscope.
I’m going to set it light an LED, but only at 50% brightness.
What we see on the oscilloscope is quite different.
If you’re thinking it looks like its just cycling off and on the power, but keeping
the voltage at 5V, you’re exactly correct.
This type of signal is called a square wave and will typically cycle by outputting zero
volts for a period of time, followed by a specific voltage such as 5 volts for the same
period of time.
What do you think the voltage reading will be if we hook this circuit up to our multimeter?
If you guessed approximately 2.5 volts you would be correct.
A 5 volt square wave voltage at 50% duty cycle will produce 2.5 volts RMS!
If I change the duty cycle by setting the PWM output on the Arduino to just 10% you’ll
see exactly what you’d expect.
Now the voltage is only 5V for 10% of the time, of zero volts for 90% of the time.
Amd this will translate to just under 1V on our multimeter.
There are two more knobs on the oscilloscope that are commonly used.
These are the horizontal and vertical positioning knobs.
Turning the horizontal position knob lets you adjust where the waveform starts and stops
on the screen and allows you to line it up with divisions should you choose.
Turning the vertical position knob allows you to move the signal higher or lower on
the grid making some signals easier to read.
Oscilloscopes generally have between 1 and 4 channels.
The probes connect to these channels using standard BNC connectors.
Having more than one channel of course allows you to view more than one signal on the screen
at the same time.
Each channel will be represented by a different color.
The probes have some pretty cool features on their own.
First, most probes have 1X - 10X button on the side of them.
Moving the button to the 10X position attenuates the probe by a factor of 10.
This is done in most brands by connecting an internal 9 Mega-Ohm resistor.
You’ll most likely use your probe in the 10X mode most of the time as it is the more
accurate setting for most applications.
At the end of the probe you’ll see the tip and a ground lead.
The ground lead or course connects to the ground on the device you are probing, or earth
ground if your device has one.
The tip of the probe opens by squeezing it, and offers a sprung hook to easily connect
to pins or wires in your electronic devices.
However, in some cases this hook is not ideal.
With most probes you can remove this hook by pulling gently to reveal a single pin probe
that can reach some hard to get places.
This is a super handy feature!
An oscilloscope can be very handy in everyday life.
For example, if you have an Arduino Uno and you think the Oscillator crystal is bad, it’s
super easy to check that on the oscilloscope.
All you have to do to check the oscillator crystal is to measure it with the scope.
First, connect the ground lead to any ground on the arduino.
The closer electrically to the oscillator, the more stable the signal will be.
Now using the oscilloscope probe with the spring hook removed, use the tip of the probe
to touch the solder pad on the output side of the crystal.
You should see a 16Mhz oscillation on the oscilloscope.
If you see any other value, it’s likely that the crystal needs to be replaced.
What if you suspect there is a problem with the SID chip in your trusty Commodore 64?
You can check that with an oscilloscope!
Carefully open the Commodore 64 making sure to disconnect the LED light so it doesn’t
get hung on anything.
I just used FB64 to mount the Standing Stones disk image and load the game.
It’s got some pretty cool intro music we can use.
Now, just touch the probe pin to the SID chips output line, pin 27 and you should see some
fantastic waveforms represented on the oscilloscope’s display that seem to match the music you hear!
Well that’s all I have for you in this video!
Be sure to like this video and subscribe to my channel if you’d like to see more videos
like this.
Thanks for watching!