THE SIMPLEST FUNCTION GENERATOR BUILT ON a BREADBOARD

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Introduction: THE SIMPLEST FUNCTION GENERATOR BUILT ON a BREADBOARD

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
9. Wires.

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.

Good luck....

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    28 Comments

    Hi, thanks your your instructable. Could you please include the gnd and power supply to the shematic? I don't know where these go

    Hi, can I replace LM324 with LT1079CN? What should I take into account? Thx!

    Please Help. How do I make the connecting interface to connect the board to an oscilloscope?

    This link https://www.efxkits.us/square-wave-generator-circuit-using-op-amp/ describes a nearly identical project and contains a more detailed schematic. I've included that schematic here, in case the link goes bad in the future. It refers to the LM1458 op amp, but I suspect than the LM324 can also be used. The LM324 is getting on in years now and there are better ones, but one of the advantages of the LM324 is that it's cheap and can be powered by a single source. I've been using the MC34074AP as a plug-in replacement for the LM324 and have been very happy with it.

    6[1].jpg

    From the LM324 Datasheet, Page 17, Figure 27:
    TI shows a square wave oscillator without the pot. In their schematic they show a resistor to the + pin (3,5,10,12 on LM324) from a v+ source. As soon as I connected v+ in this way stage 1 worked like a champ!
    The reference resistors from TI schematic are 100k.

    I've only got stage 1 working right now, but going to make the other stages next.

    Can i also run this from a 24Vdc power supply ?

    Builders can use a small Radio loudspeaker or Earphone to hear the Signals, if you want to view them obviously you need to look for an Oscilloscope or an i pad App and adapter.

    Can you please show me the setup of stage 1 alone. The other sections are working, but stage 1 isn't.

    One more thing, how do u connect the battery??

    What's the purpose of R6 on step 5: stage 3?