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When you build an experimental circuit, you will generally need to have some way to determine whether or not it is working correctly, and if so, how well. If it is not working, you'll need to locate the problem so you can fix it. To accomplish this, a wide range of test instruments has been developed. Some of these apply to many different kinds of circuits, while others are specific to one type or class of circuits.

This page lists the more common types of test instruments that you may want to use with these experiments, with descriptions of what they do and where they are useful. Some of them will be the subjects of experimental circuits themselves, so you can actually experience how they work and what they do. Others are beyond this scope, or are not feasible as experimental circuits.

Volt-Ohm-Milliammeter (VOM)

The basic test instrument in electronics work. Originally available only as an analog instrument with meter movement, it is now more common as a digital instrument (often called a Digital Multimeter or DMM). As its name suggests, it is able to measure resistance, ac voltage, and dc voltage and current over a wide range of values.

We strongly suggest you obtain and use a DMM for the experiments in general electronics. Inexpensive versions are readily available, although this instrument is too complex to be constructed as an experiment before you will need to use it. For theoretical handling of experimental circuits on these pages, you will use a virtual DMM on the screen.




Wheatstone Bridge

The Wheatstone bridge is a very simple but amazingly accurate device for making measurements. It gets applied in one way or another in a wide range of circumstances.

In the course of the experiments on these pages, you will construct and demonstrate a practical Wheatstone Bridge circuit to measure resistance and capacitance values.




Frequency Counter

As its name suggests, this instrument measures and displays the frequency of its input signal. You might also see it identified as an EPUT meter (Events Per Unit Time). This instrument operates by amplifying the input signal and clipping it into a clean rectangular waveform, and then counting the number of pulses that occur within a precise time interval (usually 1 second). The frequency counter works with any regular signal, analog or digital, over the frequency range for which it is intended.

You will construct and demonstrate a working frequency counter in the course of the experiments on these pages. You will not actually need a commercial frequency counter to perform any experiments, but you may want to obtain or build such an instrument if you plan to do much work in the eletronics field.




Audio Function Generator

This device provides one or more waveforms at frequencies ranging from approximately 0.1 Hertz (one cycle every 10 seconds) to perhaps 100 kHz. Typical waveforms are sine wave, triangle wave, sawtooth waveform, square wave, and narrow rectangular pulse. In many cases a dc offset can be imposed on the signal, or the signal can be coupled through a suitable capacitor to eliminate any dc bias. This allows a known signal to be inserted into any analog circuit being tested, so that the progress of the signal through the circuit can be traced.

You will construct a practical, working function generator as part of the experiments on these pages. It will be small enough that you can actually leave it set up on your breadboard socket if you like. Or, you can purchase one if you plan to be working with audio-frequency circuitry. It is a good idea to have a known signal source so you can test and troubleshoot other circuits.




RF Signal Generator

This is a higher-frequency version of the audio function generator. The rf signal generator produces a sine wave at frequencies ranging from 100 kHz to 30 MHz or higher (the higher the top frequency, the more expensive the instrument). It often includes a simple, 1 kHz audio oscillator which can be used to modulate either the frequency or the amplitude of the main signal.

The rf generator is primarily used to test and troubleshoot radio tuners, i-f amplifiers and detector circuits. You will not need one for the experiments on these pages, and will not be constructing such a circuit here.




Oscilloscope

The oscilloscope provides a two-dimensional visual display of a signal. Most commonly it is used to show signal amplitude versus time, thus displaying the waveform of the signal being monitored. Some oscilloscopes have two or even four inputs, all using a common time base, so you can examine and compare the signal amplitude and shape as it progresses through stages of a circuit under test.

An oscilloscope might provide interesting insight into the operation of your test circuits, but is not required here. Unless you are planning to get into electronics in a major way, you should not shell out serious money for an oscilloscope.

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