Oscilloscope mini-tutorial.

[DrNomis_44]

I was planning on using the SigJenny app on my laptop to generate some signals for us to look at with the Oscilloscope, but I got an error message, so I'm going to have to go looking for a better app.


Ok, got it all sorted now.....


I've got the app set-up to generate a 1000Hz (1kHz) Sine wave signal, here's what it looks like on the Oscilloscope screen display:




A 1kHz Sine wave signal is a useful test-signal because 1kHz is right in the middle of the audio spectrum, which normally ranges from 20Hz-20kHz, a Sine wave is one of the purest signals you can generate because it is usually just one frequency and very little extra harmonics (a harmonic is a signal that is related mathematically to the fundamental frequency, in this case 1kHz is our fundamental frequency).

Let's see what other signal waveforms look like on the Oscilloscope screen, I'm going to keep the frequency set to 1kHz in each case.....

Hmmmmm....for some odd reason, the app I'm using seems to only want to generate Sine waves even though I selected Triangle and Saw, think I need a better app to generate the proper signal waveforms.

Found something that works better....

Here's what a 1kHz Triangle wave signal looks like on the Oscilloscope screen:



And here's what a 1kHz Sawtooth wave signal looks like on the Oscilloscope screen:



Notice how our 1kHz Sawtooth waveform has a bit of ringing at the top and bottom sharp corners?, that's because it is a digitally-generated Sawtooth waveform, a Sawtooth waveform generated by an analog circuit doesn't have that ringing, but for the purpose of this mini-tutorial, the digitally-generated Sawtooth waveform is good enough.

Finally, here's what a 1kHz Square wave signal looks like on the Oscilloscope screen:



Again, we see ringing on the top and bottom of the waveform due to it being generated digitally:

In each case, I had the main Time/Div. control set to .5ms/Div., that means for every 1cm horizontal graticule mark, that represents a time-interval of .5ms (mili-seconds), each of the signal waveforms takes two 1cm horizontal graticule marks to complete one-cycle, so the total-time for one complete cycle is .5ms+.5ms= 1ms.

To calculate the frequency of the signal being displayed, you use the following formula:

F= 1/T

Where F equals the signal frequency, and T equals the total time taken to complete one full cycle.

I'm deliberately trying to keep this mini-tutorial as non-technical as possible, just so it's easy to understand, but at some stage you do need to do some maths when making measurements with your Oscilloscope.

The Oscilloscope actually gives us the ability to make a few different measurements of a signal, we have just done a time-measurement using the horizontal graticule marks, on the Screen, horizontal graticule marks refer to Time, you can also see some smaller graticule marks in-between each larger 1cm graticule mark, each of the smaller marks count as .2.

On the Screen, each of the vertical 1cm graticule marks refers to signal-amplitude, usually expressed as Volts-peak, or Volts-peak to peak, you will also see smaller graticule marks in between each of the larger 1cm vertical marks, these smaller marks each count as .2 as well.

If you set the Volts/Div. for each of the Scope's input channel to say 1V/Div, and the signal covers two 1cm graticule marks, then you can easily determine that the signal level is 2V peak-to-peak.

So, simultaneously, our Oscilloscope gives us a way to measure both signal-frequency and amplitude at the same time because the display is really just a graph of signal-amplitude versus time.


Ok, we'll continue-on next time so stay tuned......

In the meantime, here's an interesting and fun thing to try with your Oscilloscope, connect one of your Oscilloscope's inputs (Ch-A if you have a Dual-Trace Scope), up to the output-jack of one of your guitar builds via an instrument lead, and use your Oscilloscope to look at the output-signal of your guitar while plucking one of the strings with a pick.

Try comparing the output signal-level of a guitar with single-coil pickups to the output signal-level of a guitar with humbucking pickups too.