A function generator is one among the necessary gadgets of an electronic hobbyist. It is very useful in producing audio signals and even in inverter circuits. Since it is not affordable for hobbyists, I decided to make one myself with easily available and cheaper components.
I chose LM324 to generate various waveforms. It is a quad operational amplifier IC. It just needs a bunch of resistors and capacitors to build the entire circuit. It could be assembled in just 15 minutes in a bread board. I was able to produce square, triangle and sine wave with this.
Step 1: Step 1: Parts list
1. Bread Board --1x
2. LM324 --1x
3. 100K POT --1x
4. 10K (1/4 W) --7x
5. 100K(1/4W) --3x
6. 0.1uF - 2x
7. 0.01uF -1x
8. Battery --1x
Step 2: Step 2: Schematic
LM324 consists of 4 operational amplifiers. All the four op-amps are used to generate square, triangular and sine wave.
First op-amp is used to produce a square wave and it shaped into triangle wave by integrating it with second op-amp. The second op-amp is an integrator circuit.
The third and fourth op-amps are the wave shaping circuits which are used to remove the sharp edges of the triangle wave and shape it to a sine wave.
Step 3: Step 3: STAGE 1:
Stage 1 is a simple op-amp square wave generator wired as astable multivibrator. It is used just as a comparator. A fraction of output is fed back to the non-inverting(+) terminal as reference voltage. The capacitor C can charge through the trim pot R.
When the output is high, the capacitor C starts charging and once if the voltage across the capacitor reaches the reference voltage, the output is driven to negative region.
The capacitor now charges with negative polarity and once it reaches reference voltage, the output is driven to positive region.
This cycle continues and a square wave is obtained as output.
The frequency of this oscillation is given by F= 1/(2RC).
Therefore, by varying the trim pot R the frequency can be changed.
Step 4: Step 4: STAGE 2:
The stage 2 comprises of an integrator made of op-amp.
When a square wave is provided to an integrator, the square wave is converted into a triangular wave with no change in frequency.
Therefore a triangle wave is obtained as output at the end of second stage.
We have to make sure that R5 is at least ten times higher than R3.
Step 5: Step 5: STAGE 3
The stage 3 is a wave shaper stage consisting of two op-amps.
This stage is used to remove the sharp edges in the triangle wave and to make it a sine wave.
Thus the output of entire circuit is a sine wave.
The frequency of all the three waves are identical and can be varied by varying the trim pot R.
Step 6: Step 6: Breadboard Assembly
Assemble each component in the breadboard as per the circuit diagram.
If you decide to use this circuit for future use, it is better to assemble in a dot board or in a PCB.
The output may not be a pure waveform. It might have some disturbances but it is not bad when comparing the cost of buying a new one.
I hope you find it easy to understand and useful. Since the entire setup costs less than 1$(excluding bread board and battery), it is worth to give a try.