Low Frequency Waveform Generator

A function generator is an important piece of equipment used in every electronics laboratory. It is widely used to test op-amp circuits, digital to analog converters and vice versa. Here we demonstrate the construction of a low frequency function generator whose range is from 1Hz to 1KHz and can synthesize various types of waves. This is an inexpensive form of a function generator. The output obtained from the device is spectrally pure as verified using a spectrum analyzer. Here are a few snaps of development and final stages of the project.

The circuit uses AT89S52 as the central brain. It also houses a DAC, an op-amp, an LCD and a set of switches. The LCD and switches are for user interfacing. The  circuit employs a method called DDS (Direct digit Synthesis) for generating analog signals. The low frequency limitation of the project stems from the operation of 8051 controller used in the project. It has a clock frequency of 11.0592 MHz but since it contains 12 T-States for every instruction; the instruction cycle duration becomes 9.02 us. Unlike many of its contemporary micro controllers like PIC AVR MSP 430 etc. 8051 also has many instructions that occur in multiple instruction cycles which further degrades the speed of operation.

The circuit can generate all types of analog signals like square wave, sawtooth, ramp, staircase, etc. with variable amplitude (from 0 - 5V) and variable time period (1 - 1000 ms)

Low Frequency Waveform Generator in action....producing a sawtooth wave of of amplitude 4V and frequency ~1 KHz.