How to Build a Sine Wave Generator with a 555 Timer Chip

Sine wave

In this circuit, we will show how we can build a sine wave generator with a 555 timer chip.

A sine wave generator is a device which can generate sine waves.

Sine waves are waveforms which alternate in values during a cycle. It has a peak value, the highest amplitude it attains and a trough value, the lowest amplitude it obtains. The sine wave in between the peak and trough takes on an infinite number of values in between the peak and trough value.

Sine waves are actually very common. One of the most frequent places you will find them is in household electricity sockets. Out of household electricity sockets comes out AC sine voltage signals.

In the United States, the sine waves have a frequency of 60Hz, meaning there are 60 cycles in a second. In countries throughout the world, the frequency is either 50Hz or 60Hz. In the United States, the amplitude of AC voltage is 120V or 240V. Throughout the world it varies from as low as 110V to 240V.

You will also see sine waves in function generators. Function generators usually can output AC signals in sine wave, square wave, or triangle waveform.

Sine waves are also used a lot in acoustics.

In this circuit we will use a 555 timer to create a sine wave signal that can be used for a variety of purposes.

Components Needed

  • 555 Timer Chip
  • 2.2KΩ resistor
  • 100nF ceramic capacitor
  • 10nF ceramic capacitor
  • 1μF ceramic capacitor
  • 470μH inductor

The 555 timer can be obtained very cheaply from pretty much any electronic retailer.

The 555 timer is an 8-pin chip.

If you want to know all the pinout of the 555 timer, what each pin is and what each pin does, see 555 Timer Pinout.

In this circuit, we will connect the 555 timer to be in astable mode.

In this mode, the 555 timer will go from HIGH to LOW, HIGH to LOW, HIGH to LOW.

The connections are shown below.

Sine Wave Generator Using a 555 Timer

The sine wave generator circuit that we will build is shown below.

Sine wave generator circuit with a 555 timer

The breadboard schematic of the above circuit is shown below.

Sine wave generator breadboard circuit with a 555 timer

So, first, for the power requirements of this circuit, we use 4.5V to the 555 timer chip. This 4.5V goes to pin 8 and pin 4. Pin 1 is grounded.

This 555 timer is in astable mode.

Astable mode can produce digital square waveforms that go back and forth between HIGH and LOW.

In this circuit, the RC netowrk is composed of a 2.2KΩ resistor and a 10nF capacitor. Doing the math for this RC network using the formula, F= 1/2πRC, we obtain a frequency of approximately 7237Hz (F= 1/2(3.14)(2.2KΩ)(10nF)= 7237Hz).

So our square wave signal with the current values of the resistor and capacitor used has a frequency of approximately of 7.2KHz.

But we want this signal to turn into a sine wave.

How do we do this?

We use an LC resonant circuit at the output where the square wave signal is produced.

With an LC resonant at the output of the 555 timer, the square wave signal is converted into a sine wave signal, a signal that is very much sine wave like.

But in order for this to happen, the right values must be chosen for the LC resonant circuit, or else it will not work.

The whole purpose of a resonant circuit is that with the right values, the output signal resonates. In mathematics, a sine wave is the perfect model representation of resonance. When resonance is achieved and it can be through an LC circuit, the output signal will be a sine wave, because a sine wave represents resonance.

So with an LC network, we're able to resonant the square wave produced by the 555 timer chip into a sine wave.

But, again, in order for this to occur, we must choose the right values of the inductor and the capacitor in the LC network in order to achieve resonance.

So, before, as we did the math for this circuit, the output square wave is approximately 7.2KHz, so we have to create an LC network that resonants at that frequency in order to get a sine wave output.

So we need to calculate values for the LC network where the resonant frequency is just about 7.2KHz.

So there's a formula to calculate LC resonance. This formula is, frequency= 1/2π√LC. With this formula, we can calculate the values needed in order to calculate a frequency that is just about near 7.2KHz. So I did the math and I arrived at the values of 470μH for the inductor and 1μF for the capacitor. Plugging these into the formula, the frequency is 7.34KHz, which is very close to the 7.2KHz output by the square wave. So the values are close enough so that this circuit works. Obviously, the closer you get these 2 values to match, the more perfect of a sine wave you get at the output. But, again, this circuit works, as evidenced by the video you can watch below.

So that's how this circuit operates.

A 555 timer chip can produce square wave signals easily. It's very good at producing square waves. You simply have to put the 555 timer in astable mode and it outputs square waves.

Then after that, all you have to do is place an LC resonant circuit at the output of this square wave to have it change into a sine wave.

And that's all that's required to get this to work.

Realize that this circuit is precise. Like I said, you have to use the right values for the LC network to achieve and you also have to use the right voltage. This circuit gets 4.5V to the chip. The circuit won't resonate if the voltage is off. 4.5V is right where it needs to be to achieve resonance. If you vary the voltage much from this, the circuit won't work. So you have to watch a lot of parameters. But the circuit works very well if you're in the right range of value. Anywhere near 4.5V works very well.

Obviously, there are modifications you can do to this circuit. You can change the frequency of the output signal by changing the values of the RC network. If you increase the values of the RC network, this decreases the frequency. Likewise, if you decrease the values of the RC network, you increase the frequency.

To create a 6Hz signal, R1= 10MΩ and C= 10nF.

To create a 600Hz signal, R1= 100KΩ and C= 10nF.

To create a 134Hz signal, R1= 470KΩ and C= 10nF.

To create a 1.7KHz signal, R1= 33KΩ and C= 10nF.

To create a 43KHz signal, R1= 1KΩ and C= 10nF.

To create a 180KHz signal, R1= 150Ω and C= 10nF.

To create a 252KHz signal, R1= 100Ω and C= 10nF.

But remember if you modify the frequency of the square wave signal, you have to change the values of the LC network, so that resonance can be achieved for that frequency.

So it requires a good deal of math.

But this is how a sine wave generator circuit can be built with a 555 timer chip.

To see how this circuit works in real life, please see the video below.

Related Resources

How to Build a Square-to-Triangle Wave Converter Circuit

How to Build a Square-to-Sine Wave Converter Circuit

How to Build a Triangle Wave Generator Circuit with a 555 Timer

How to Build a Sine Wave Generator Circuit with a Single Transistor

How to Build a Ramp Generator Circuit with Transistors

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