Waveform Type Detector

[etumcen]

Hi.I have a project,i haven't an idea yet,firstly i want to receive your ideas and then design my circuit.If you have an idea about this,please share with me so i can evaluate these and make my circuit more accurate.Project is as following.
WAVEFORM TYPE DETECTOR
The circuit will detect the given input waveform.The input waveform will be a triangular,sine or square wave,with a frequency of having 1000-3000 Hz and having an AC amplitude of 2V to 4V and a DC offset of -5 to 5 volts.In this circuit project,using an multimeter,voltmeter,oscilloscopes or any instrument which measures voltage or current is not allowed.But,red and green LEDs can be used as indicators.

 

[audioguru]

Didn't your teacher teach you the differences between the triangle, sine and square waveforms? Aren't the differences in your textbook? Can't you hear the differences?
Then make a circuit that lights LEDs with those differences.

 

[kchriste]

You would basically make a filter to filter out 1000-3000 Hz (A slightly larger band will be more practical) and then detect any harmonics that remain. I'll leave it to you to figure out which waveforms will produce the least and most harmonics.

 

[etumcen]

I don't know the harmonic notion in circuits.Can you explain what you mean?

 

[etumcen]

Additionally,i don't know how i can calculate harmonic of a wave.Is it possible for you to explain some how it's calculated?

 

[etumcen]

I searched but i want to ask a question.Does a filter only work with regarding to frequency and also does it depend on waveform to pass a signal?

 

[audioguru]

There is nothing to calculate. A sine-wave is just a single fundamental frequency without any harmonics. The 2nd harmonic is two times the fundamental frequency. The 3rd harmonic is 3 times the fundamental frequency. The 4th is 4 times etc.

All you need to do is learn about harmonics from your teacher, textbook or Google. Then learn about sine, triangle and square waves and you will know how to detect which type is which.

 

[audioguru]

Does a filter only work with regarding to frequency and also does it depend on waveform to pass a signal?

There are lowpass, bandpass and highpass filters:
1) A lowpass filter passes the lower frequencies and reduces higher frequencies. You need to detect if the waveform has higher frequencies (harmonics) so you don't want a lowpass filter.
2) A bandpass filter passes a few frequencies and reduces lower and higher frequancies. You don't need one.
3) A highpass filter passes higher frequencies and reduces lower frequencies. Then it will pass the harmonics and reduce the fundamental frequency, so its output will have a different signal level for the different types of waves. You are on the correct path.

 

[etumcen]

I cannot imagine this.I understand that a sine wave and square wave input with same frequencies can pass from a highpass filter.So how can i seperate them by looking to the output signal?Sorry,i cannot understand.

 

[audioguru]

A 1000Hz sine-wave is only 1000Hz. It has no harmonics.
A 1000Hz square-wave is 1000Hz plus odd-numbered harmonics which are 3000Hz, 5000Hz, 7000Hz, 9000Hz etc.

If a 1000Hz sine-wave is passed through a 3000Hz highpass filter then only a little 1000Hz gets through so the output level will be low.
If a 1000Hz square-wave is passed through a 3000Hz highpass filter then all harmonics will be passed and will create a high output level.

You know that a low output level from the highpass filter indicates a sine-wave and a high output level indicates a square-wave.
Then learn the levels of the harmonics of a triangle wave and your project is nearly done.

 

[etumcen]

Ok,thanks for your help.I don't know anything about filters.We don't learn such a thing.I'm a second year student and ı only study circuit theory one in this term.But i will try to learn filters and design my circuit.If i will have a question again,i can call a help from you.

 

[etumcen]

İ ve designed a different circuit with two differentiator and leds other than highpass filter..Each Led is after the dİfferentiator.If we give a sine signal as input then it can pass away from each differentiator.İf we give a triangular wave it an pass first differentiator and output in here is a square wave and tihs cannot pass second one ,that is output will be zero.If we give a square wave it cannot pass any differentiator.So,for a sine wave 2 leds will light,for triangular only one and for square wave none of them will light.Is there a false thing in this circuit or is it absolutely false?If you share with me your ideas about circuit please tell me.It's some urgent.

 

[audioguru]

A differentiator is the same as a highpass filter that I have been talking about. It reduces the level of lower frequencies including the fundamental frequency, so it will have a low output level for a sine-wave input.
If a triangle-wave is the input to a differentiator then its output is a low level of the fundamental frequency and a higher level of the harmonics.
If a square-wave is the input of a differentiator then its output is also a low level of the fundamental frequency and a higher level of the harmonics.

The harmonics in a square-wave are at a higher level than the harmonics in a triangle-wave.

 

[etumcen]

Please don't tell me with harmonics and don't use complex terminology.If you can explain more simple with understoodable words,it will be more benefit to me.I cannot underestand because i am a beginner in circuit design and electric-electronics field.Does this circuit make sense,does it work,is it logical?

 

[audioguru]

If we give a sine signal as input then it can pass away from each differentiator.

What do you mean by "pass away"? A low frequency sine-wave has its level reduced by a differentiator.

İf we give a triangular wave it an pass first differentiator and output in here is a square wave and tihs cannot pass second one,that is output will be zero.

No. The harmonics of a triangle wave will pass through the differentiator.

If we give a square wave it cannot pass any differentiator.

No. The harmonics of a square-wave will pass through a differentiator.

So,for a sine wave 2 leds will light

No. The output level of a low frequency sine-wave will be low.

for triangular only one and for square wave none of them will light.

No. The harmonics of a triangle-wave are strong and the harmonics of a square-wave are stronger, so the LEDs will light.

Please don't tell me with harmonics and don't use complex terminology.If you can explain more simple with understoodable words,it will be more benefit to me.I cannot underestand ...

the differences beween the waveforms are their harmonics. I used simple terminology. Your project is way above your understanding about waveforms.

 

[Hero999]

Please post schematics of all the circuits you've tries and details of what frequency(ies) you're using.

Are you just using one frequency or many?

What about the amplitude?

 

[etumcen]

I've given the values of given signals to the circuit.The circuit have to work for all the values of these,not a particular signal.A signal will be chosen between the given values randomly,then circuit will anlayse the signal waveform taht we understand by looking whether leds are ligthing or not.