SIMPLE FUNCTION GENERATOR KIT INSTRUCTIONS

Table of contents

1. Introduction
2. Schematic
3. Simulation
4. How It Works
5. Component List
6. PCB
7. Project Ideas
8. Going Further

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SCHEMATIC

SIMULATION

INTRODUCTION

In just about every electronic circuit there will be some signal that changes with time and in many circuits, this signal may be continuous. For example, the electricity from the mains supply has a sinusoidal shape (like an ocean wave). Another example would be the clock for a computer which has a square shape.

Imagine a scenario where a digital circuit has been created and requires a clock from an external source. One could be built especially for the task however the clock source would most likely have a fixed frequency. Even if one was designed to have a variable frequency (which takes time), the device would only output a square wave. This is where the humble function generator steps in!

Not only does the SFG (Simple Function Generator), have both a square and triangle output but the frequency is also adjustable. The square and triangle waves are generated by the same source and thus are always in the same phase which means that the two waveforms follow each other constantly (useful if both waves are being used). But how does this circuit work? What active devices are used to create the oscillations and how is the frequency adjusted? Let's find out...

HOW DOES THE SIMPLE FUNCTION GENERATOR WORK?

The Main Components

The Simple Function Generator circuit uses special component arrangements such as Schmitt triggers and integrators. To properly understand how this circuit operates it is important that the following is pre-studied:

- Op-Amps

- Schmitt triggers

- Integrators

How The Simple Function Generator Oscillates

The first op-amp with R1 and R2 is configured as an inverting Schmitt trigger. The second op-amp with C1 and the potentiometer (POT), form an integrator. Assuming the Schmitt trigger output is 0V the integrator will begin to discharge C1. This forms the downward slope of the triangle wave.

The Schmitt triggers output will rise to VCC once the output voltage on the second op-amp falls below the Schmitt triggers lower threshold voltage. As a result of this, the output of the integrator will begin to rise because C1 will begin to charge. This forms the upward slope on the triangle wave. Eventually, the output of the integrator will become larger than the Schmitt triggers upper threshold voltage.

When this happens the Schmitt trigger will output a voltage of 0V which will result in the output of the integrator to fall. This process results in the constant production of both a square wave and a triangular wave, in other words, it oscillates.

The rate at which the oscillation occurs (i.e. the frequency), depends on the resistance of the POT and the capacitance of C1. Since a variable capacitor would not be ideal in this situation (as they are only available with small ranges), a potentiometer is used instead. By adjusting the resistance of the POT the frequency of the produced wave will change.

Component List

Component	PCB Reference	Quantity	Looks Like
8 DIP Socket	U1, U2	2
LM358 Dual Op-Amp IC	U1, U2	2
100nF Ceramic Disc Capacitor	C1, C2, C3	3
47K Resistor	R2	1
100K Resistor	R1, R3, R4	3
100K Linear Potentiometer	RV1	1
Red Wrire	VCC	1
Green Wire	TRI	1
Blue Wire	SQUARE	1
Black Wire	GND	2

PCB

PROJECT IDEAS

Bench Function Generator

Function generators are extremely expensive pieces of equipment that will likely contain many features you don't need. As such, the Simple Function Generator Kit provides an excellent alternative that is not only much cheaper but easier to use and interface with. If you require more complexity, you can add extra circuits to the output of each waveform, and enclosing the Simple Function Generator in a case can make a very neat and practical project!

Synthesiser

The Simple Function Generator produces both square and triangle waves which are both highly popular with old consoles. As such, the Simple Function Generator kit can be used as a synthesiser either on its own, or combined with external analogue voltages. Furthermore, both the square and triangular waves can be mixed together to create some really unusual sounds!

Sine Wave Source

Did you know that if you pass a triangular wave through several low-pass filters you can create a sine wave? As such, a sine wave source can be made from the Simple Function Generator, and this can be used for creating inverters, modulation systems, and so much more!

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