## A square wave test signal generator for testing electronic projects (1)

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• Ian Purdie s A square wave test signal generator for testing electronic projects MULTIVIBRATORS Your first test instrument - a multivibrator as a signal
Message 1 of 3 , Oct 28, 2002

## Ian Purdie's

A square wave test signal generator for testing electronic projects

# MULTIVIBRATORS

#### Your first test instrument - a multivibrator as a signal generator

Assuming you have acquired or have access to the most basic of construction equipment:

(a) a small tip soldering iron - about 15 watt
(b) some small gauge resin cored solder
(c) a pair of diagonal cutters
(d) a pair of small pointy nose pliers
(d) and a multimeter - preferably digital
and you have some basic soldering skills or you can practice on some scraps you can now proceed to constructing the most valuable piece of test equipment you will probably ever construct.

##### WHAT THE HELL IS A MULTIVIBRATOR?

Firstly let's look at Fig 1. which is meant to represent a snapshot of a square wave signal as it might be seen on a simulated oscilloscope.

Now over the green background of our simulated oscilloscope (hereafter called a CRO - short for Cathode Ray Oscilloscope) you can see black / grey horizontal and vertical graduations. They represent the horizontal time base settings and the vertical amplifier settings. In Fig 1 we have set our vertical amplifier to represent 5V per division and the horizontal timebase setting to represent 100 micro-seconds (100 us).

As you can clearly see from this simulated signal it's value goes from zero volts (the centre horizontal line - at point A) up vertically to the next horizontal line (representing 5 volts - at point B). The signal continues horizontally for one graduation to point C before returning to zero volts at point D. Our signal continues horizontally for another graduation at zero volts to point E.

Fig 1 Oscilloscope Representation of a square wave signal

The total period of time our signal takes to complete one full cycle (Points A through to E) is two graduations of the horizontal scale, each of which represent 100 us, total time is 2 X 100 us.

Frequency = 1 / time which is 1 / 200 us OR

1 / 0.0002 = 5000 Hz OR 5 Khz

Now I've gone a long winded way about describing for you what a square wave signal (this one at 5 Khz) looks like. It is generated by a "multivibrator".

O.K. get to the point - what's a multivibrator? It is simply an electronic device which simply turns on and off at a pre-determined rate, in this case 5 Khz or 5,000 times a second.

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