BUILD YOUR OWN WAVEFORM GENERATOR FOR YOUR ELECTRONICS LAB

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If you need testing your audio projects or repairing audio amplifiers, surely you will need a waveform generator (WFG) to check if the signal you introduce in your equipment goes out without any distortion. Also, if you are studying operational integrated circuits this project will be a handy tool to your experiments.

I have built my waveform generator with the monolithic integrated circuit ICL 8038 which allows you to get sine, triangular and square wave with very simple circuits and quite easy to design...

The components you need for your project are quite few, three or four resistors, one potentiometer, two adjustable resistors and three or four capacitors. All this makes the project quite attractive.

And if you only want to see how the 8038 ICL works a breadboard will ensure a speedy way of been acquainted with this interesting integrated. To have a new set for my electronics lab I decided to mount the circuit in a permanent form. So I completed the above components with a 10 K log, 20 turn pot and two selector keys to change the range of frequencies and the wave forms at the output of the set.

8038 IC	Two 5.6K Resistors
741 IC	100K Adjustable Resistor
0.1 uF Capacitor	15K Resistor
4.7 nF Capacitor	10K Resistor
2.2 nF Capacitor	20K Resisto
220 pF Capacitor	5K Potentiometer
10K 20 turn Potentiometer	Two 3pst Commutator Keys
1K Adjustable Resistor	1K Resistor
10M Resistor

The drawing below shows the schematic for the WFG. In this diagram you note another integrated circuit, the famous 741, which mission is to buffer the output of the 8038 IC and at the same time eliminate the influence that could have the equipment you are testing on the generator itself.

The placement and values of the components are in the picture of the perforated board I have used for this part of the project.

As you could see the schematics of this generator is fairly simple, and to simplify more its construction I divided the project into four modules that can be independently built, and then joined together for a complete set.

First, it is a good thing starting with the power source so that when you finish building the generator module you could test it...either with an oscilloscope or with a crystal earpiece in the region of low frequency audio waves. A transformer reduces the mains 120 or 220 volts to a double voltage of 9 volts that allows us to construct a double voltage power source in case we want to feed the operational integrated with a 5 volts + and a 5 volts -- with a central ground of zero volts. The second module is the wave forms generator itself, that fed with 10 volts coming from the power source, works quite well. You can obtain immediately after its building a sine wave from pin # 2 of the 8038 Ic, a triangular wave from pin # 3 and a square wave from pin # 9. An oscilloscope is the best way of checking the forms sourced by the mentioned pins. To have a set of frequencies ranges that in this generator reach up to about 30 kilohertzs, I built a third module, very simple, with only three capacitors 4.7 nF, 2.2 nF and 220 pF. You can even simplify more the project using a single capacitor of 4.7 nF from pin # 10 to ground.

Finally the fourth module is the 741 buffer that isolate the 8038 Ic from the load that represents the circuit under testing. At the same time this buffer allows us to regulate the voltage output of the generator with a 5K potentiometer. A few more components can be added, as a switch, a pilot led, a fuse. . . screws, nuts, connecting cables and a cabinet, all these to your taste.

WARNING : This module to feed the Wave Form Generator implies the risk of electric shock. So, if you are not an expert DO NOT BUILD IT. Voltages coming from the mains, either 120 volts or 220 volts are extremely dangerous. Building this project without enough knowledge of high voltage electricity is your own responsibility!

The Wave Form Generator can be driven with two 9 volts batteries, which are quite safe. This power source is able to source one + 5 voltage and another --5 volts, with a neutral (zero) voltage. This kind of power sources are design especially to feed operational integrated circuits. Usually the forms generators have operational integrated ICs to improve its wave forms and to isolate and buffer the output from, and to, the loads connected to them.

Taking advantage of the 7805 and 7905 Ic regulators it is very simple to build and efficient power source. To smooth the pulsating current coming from the rectifier diodes two electrolytic 1000 uF are used.

Two more electrolytic 100 uF have a further mission of improving the current quality obtained from the 7805 and 7905 regulators. Finally another 100 mylar or ceramic cap helps filtering possible glitches and interferences coming from the mains. In this way this power source delivers to your project a double 5 volts DC current of the same practical quality as the one coming from batteries.

Reductor Transformer (120-220 to double 9 volts)	7905 Voltage Regulator IC (Integrated Circuit)
A fuse	100 nF Ceramic or Mylar Capacitor
Two Rectifier Diodes (1N5625 or equivalent)	1.5K 1/2 Watt Resistor
Two 1000 uF 25 Volts Electrolytic Capacitor	LED Diode
7805 Voltage Regulator IC (Integrated Circuit)

NOTE: Please be careful with the pin setup of the 7805 and 7905 voltage regulator IC's. The pin setup of the 7905 IC is different then that of the 7805 IC pin setup!

After the Waveform Generator Project has been completed, here is the way of testing it and adjusting the waveform...

Once we have finished mounting our project, either in a breadboard or in a permanent way, some test and adjust is indispensable. We need for this purpose and oscilloscope and a frequency meter. If your oscilloscope allows you to measure frequencies, then the frequency meter is not absolutely necessary. With your oscilloscope or with the frequency meter seek for a frequency of 1000 cycles, ( one kilohertz ).

First...we will check the wave form coming out from pin # 2, that must have a sine form though perhaps not quite correct at this moment. To get a perfect sine wave trim the 100 K adjustable resistor till the point in which you will find the best form for a sine oscillogram. Now we have to find a duty cycle of 50% for the square wave. That means that the bottom trace of the oscillogram be equal to its upper trace. Trimming the 1 K adjusting resistor and observing the screen of your oscilloscope you will get easily the 50% duty cycle. This two adjustment also perform a perfect triangular wave form automatically, what means that you have a wave form generator as a valuable instrument for your electronics laboratory.

They have plenty of information with schematics to demonstrate the many special characteristics of this interesting integrated circuit.