# How to Use an Oscilloscope

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Contributors: jimblom

## Basics of O-Scopes

The main purpose of an oscilloscope is to graph an electrical signal as it varies over time. Most scopes produce a two-dimensional graph with time on the x-axis and voltage on the y-axis.

An example of an oscilloscope display. A signal (the yellow sine wave in this case) is graphed on a horizontal time axis and a vertical voltage axis.

Controls surrounding the scope's screen allow you to adjust the scale of the graph, both vertically and horizontally -- allowing you to zoom in and out on a signal. There are also controls to set the trigger on the scope, which helps focus and stabilize the display.

### What Can Scopes Measure

In addition to those fundamental features, many scopes have measurement tools, which help to quickly quantify frequency, amplitude, and other waveform characteristics. In general a scope can measure both time-based and voltage-based characteristics:

• Timing characteristics:
• Frequency and period -- Frequency is defined as the number of times per second a waveform repeats. And the period is the reciprocal of that (number of seconds each repeating waveform takes). The maximum frequency a scope can measure varies, but it's often in the 100's of MHz (1E6 Hz) range.
• Duty cycle -- The percentage of a period that a wave is either positive or negative (there are both positive and negative duty cycles). The duty cycle is a ratio that tells you how long a signal is "on" versus how long it's "off" each period.
• Rise and fall time -- Signals can't instantaneously go from 0V to 5V, they have to smoothly rise. The duration of a wave going from a low point to a high point is called the rise time, and fall time measures the opposite. These characteristics are important when considering how fast a circuit can respond to signals.
• Voltage characteristics:
• Amplitude -- Amplitude is a measure of the magnitude of a signal. There are a variety of amplitude measurements including peak-to-peak amplitude, which measures the absolute difference between a high and low voltage point of a signal. Peak amplitude, on the other hand, only measures how high or low a signal is past 0V.
• Maximum and minimum voltages -- The scope can tell you exactly how high and low the voltage of your signal gets.
• Mean and average voltages -- Oscilloscopes can calculate the average or mean of your signal, and it can also tell you the average of your signal's minimum and maximum voltage.

### When to Use an O-Scope

The o-scope is useful in a variety of troubleshooting and research situations, including:

• Determining the frequency and amplitude of a signal, which can be critical in debugging a circuit's input, output, or internal systems. From this, you can tell if a component in your circuit has malfunctioned.
• Identifying how much noise is in your circuit.
• Identifying the shape of a wave -- sine, square, triangle, sawtooth, complex, etc.
• Quantifying phase differences between two different signals.