If you’re doing any advanced electronics repair, troubleshooting, or reverse engineering, you’ll definitely need an oscilloscope. For many years, oscilloscopes were purely analog, using vacuum tubes and electron beams to “paint” the signals onto a phosphor screen, but modern oscilloscopes are now digital and can store signals for later viewing. Since a full how-to on oscilloscopes could fill a small book, we’ll cover just the basics of using one to get you started working with these seemingly complex tools.
In the simplest terms, an oscilloscope is a device for showing a graph of how an electrical signal changes over time. The vertical axis of the graph represents voltage, and the horizontal axis represents time. Because digital storage oscilloscopes use an analog-to-digital converter to change measured voltages into digital information, the scope is able to store a series of samples in order to create an approximate waveform and display it on its LCD screen. The waveform can then be analyzed or saved for later review.
Most of the controls on an oscilloscope deal with adjusting the vertical, horizontal, or trigger settings, and they are grouped accordingly into separate sections on the control panel.
GENERAL OSCILLOSCOPE SPECS
BANDWIDTH describes the range of frequencies the oscilloscope can reliably measure.
SAMPLING RATE governs how many times per second a signal is read. Since digital scopes take samples of a signal in order to reconstruct a waveform, the higher the sample rate, the more accurate the displayed waveform.
RESOLUTION describes how precise the voltage measurement of a signal is.
TIME BASE allows you to control how frequently a digital scope digitizes samples from an input signal. When you adjust the horizontal scale on the scope, you are adjusting the time base.
CHANNELS are the number of signals a scope can read, with each signal being input in a separate channel. Most mid-level oscilloscopes can display two or more signals on a screen at a time.
In order to measure a signal, you’ll need to connect one of the scope’s channels to it with a probe. Probes have sharp tips for probing into a circuit, and there are clip attachments that can make latching onto a wire or pin easier. The ground clip on the side of the probe should be connected to a common ground point for the circuit being tested.
There are many kinds of probes, but most scopes come with switchable 1X/10X attenuated probes. Attenuated probes increase the accuracy of high frequency signal measurement, but they reduce the measured amplitude of the signal. You can leave the probe at 10X for most measurements, but you may need to switch to 1X for low voltage signals.
The trigger settings tell the scope what parts of a signal to “trigger” on and start sampling. This helps stabilize the wave displayed on the screen and makes it appear to be static.
This knob sets the voltage level that will trigger the scope.
The various trigger types set the kind of wave shape or pattern that the oscilloscope triggers on. Common types include edge, pulse, and delay. For more in-depth descriptions of the trigger types available on your oscilloscope, it’s a good idea to consult the manual.
Most oscilloscopes have multiple trigger modes, but the most common are normal, single, and automatic. Normal mode triggers the collection of a waveform only when the signal reaches the set trigger conditions. Single mode waits until the trigger condition is detected, then acquires a single waveform and stops. Automatic mode starts the collection of a waveform even when the trigger conditions have not been reached, forcing it to trigger after a specific period of time.
The horizontal axis of the oscilloscope screen shows the duration of time for a waveform.
This knob allows you to control the viewed portion of the waveform in its duration. You can think of this as moving the wave left or right.
This knob changes the time base, allowing you to display a smaller or larger chunk of time of the waveform, changing the seconds per division shown.
The vertical axis on the oscilloscope screen shows the amplitude of a waveform.
This knob adjusts the voltage offset of the displayed signal, moving it up or down on the display.
This knob adjusts the scale of displayed voltage on the screen, changing the volts per division displayed.
This may be a button, or it may be in a menu setting, but it controls whether a channel is AC, DC, or ground coupled. DC coupling shows all of the input signal, while AC coupling blocks any DC component of the signal so that you see the AC portion centered on zero volts. Ground coupling shows you ground, and is useful as a reference when comparing signals from multiple channels.
Many oscilloscopes have a “MATH” button, which can perform operations on the displayed waveform and overlay the result on-screen. This is useful for performing advanced analysis of waveforms on the fly.