Basic functions

An oscilloscope, really, does only one thing: it captures a representation of a live signal from a test circuit and displays it on a screen. Most often, this representation is the voltage of the signal as it changes over time.

Based on the information that the oscilloscope captures about the signal, modern digital oscilloscopes ofter two other important functions: 

1. the automatic measurement of various parameters of the signal, like its frequency, peak-to-peak voltage, duty cycle and rise time, and 
2. For signals that encode information, to decode that information and display it on the screen. For example, if the oscilloscope has captured the waveform that encodes serial UART information, we can set it so that this information is extracted from the waveform and displayed on the screen.

Almost all modern oscilloscopes offer these capabilities. The extend of their ability to automatically measure and decode differs between models and budgets.

Let’s have a closer look at the basic functions on a digital oscilloscope.

In this example, I’m chaining the duty cycle of a PWM signal using a potentiometer, and the oscilloscope is able to show the signal as it changes on the screen. 

In this example, also notice the row of measurements below the graph. Those are also updated in real time.

Capture a waveform

Often, we want to capture or “freeze” a waveform so that we can examine it more closely. This allows us use to use tools like the cursors or enable multiple automatic measurements to look at specific parts of the waveform that is of interest. 

In this small example, which comes from one of the experiments in Oscilloscopes for Busy People, I have captured a single waveform that was produced by the press of a momentary button. With the waveform captured, I can then go ahead and use the cursors to make a measurement. At the top right corner of the oscilloscope, notice the red “Run|Stop” button, indicating that what I am looking at is the waveform captured and frozen in time, not a live waveform.

Modern oscilloscopes can detect many kinds of signals out of the box based on the changes in the voltage over time. 

Most oscilloscopes have an automatic trigger function that can figure out how to capture regular, periodic signals without the user having to define its characteristics. This makes oscilloscopes user friendly so that people with no experience in using them can make simple measurements.

On top of this, oscilloscopes offer many types of signals that we can select and configure manually. In the screenshot in this example, I have set my oscilloscope to look for the most common kind of signal change, an Edge, coming from Channel 1, that goes from High to Low, and that is triggered when voltage drops below 800 microVolts (uV).

In the experiments in this course, I’ll show you how to use a variety of triggers, like Edge, RS232 and I2C.

In this video clip, the oscilloscope is automatically measuring the frequency, period, and the maximum voltage of the waveform on the screen.

It’s doing this “live” and updates these measurements multiple times per second. You can see the results of the measurements just below the graph. The measurements include the current measured value, the average, minimum and maximum values.

A more advanced, but common, feature of modern digital oscilloscopes is the ability to decode a signal that contains information. When two devices communication, they use a specific protocol so that data can travel between them. For example, in micro controller and microcomputer applications, common protocols are serial UART, I2C, SPI, and CAN.

The protocol describes how a value, like a number or a character, is encoded into a waveform with a specific shape.The waveform, with this shape, contains information. At the receipt end, a device reverses the translation to extract the information contained in the waveform.

Oscilloscopes with decoding capability can eavesdrop in the communication between two devices, and extract the information that is contained in the waveform, as it travels through the wire.