Help Needed

[raviram87]

Hi to every one out there....

I want to build a circuit that has the capability of measuring the fundamental frequency of an incoming periodic wave. I do not want to use any microcontroller.
Initially i thought of using the concept of peak detection and comparison.. The distance between the two peaks will give the period. But what if the signal has multiple peaks in the same period???
I REQUEST EVERYONE TO PLEASE SUGGEST ME CIRCUITS FOR THIS CONCEPT...
PLEASE... PLEASE

 

[Analog]

Well... You need to be more specific about the frequency range of the incoming signal, and the voltages seen... A low pass filter will generally eliminate the harmonics and produce a fundamental, but the specifics mentioned above are important. If you don't want to use a microcontroller, what are you suggesting? A purely analog circuit, or the use of discrete TTL chips? Need more details here.

 

[raviram87]

ya... thanks for the reply... i am suggesting a purely analog circuit...

are such circuits possible??? say using the help of op amps??

i got one idea.... say i have a sinusoidal signal as the input. now i go on time shifting the signal and use a comparator to compare the original signal and the times shifted signal.... and measure the time shift to give an indication of the period....

will this idea work?? are there any such circuits that shift a signal?? how do you measure such time shifts???

 

[Nigel Goodwin]

You need to be FAR more specific about EXACTLY what you're wanting to do, it's much too vague so far!.

 

[raviram87]

ok sir.... let me try...

my aim is to build a circuit that is capable of measuring the frequency or period of a given periodic signal. The signal can have multiple zero crossings or multiple peaks in the same period. and i need to display the period of the signal in say a bcd display unit.

i do not want to use a microcontroller. i learnt in the internet that this process is known as PITCH DETECTION. but they have explained using DSP processors which i do not know about.

are there simple circuits available to accomplish this task?? say using op amps or devices about which i have an idea of...

THE INPUT SIGNAL IS PERIODIC AND I NEED A CIRCUIT THAT CAN MEASURE THE FREQUENCY/PERIOD OF THAT SIGNAL USING SIMPLE ELECTRONIC DEVICES...

Thank you sir.... hoping a positive reply from you!!!

 

[Nigel Goodwin]

You still haven't said what it is?, are you trying to build a guitar tuner or something of that sort?.

 

[RadioRon]

This sounds quite difficult to implement in a circuit without using a processor/dsp. The problem is that we have a complex spectrum consisting of a fundamental, its harmonics and potentially other fundamentals and harmonics as well.

Hmm, one approach might be to create a sort of simple spectrum analyzer circuit, one that tunes a detector through a range of frequencies. As the frequency is swept, the circuit notes where the maximum output amplitude is and records what frequency that occurred at. Then reports the period for that frequency. Not easy to do without a processor.

Another approach might be to create a tuneable low pass filter. You sweep the clock for this filter from highest to lowest frequency and note when the output level drops more rapidly. I would imagine this point is around the fundamental. Then you use a simple zero crossing period counter to measure the period of what is coming through the filter. Also sounds difficult.

 

[Russlk]

A PLL might solve your problem, if the extraneous zero crossings are random, the PLL will latch onto the fundamental and you can measure the VCO frequency to determine the input frequency.

 

[raviram87]

sir, this is not with regard to any guitar tuner...

all i am trying to do is to build a circuit that can measure the frequency of any given periodic signal..

i have attached a picture of a signal... say this is the given signal... then i want to design a circuit in such a way that this circuit can tell me the fundamental frequency of the signal.... i am not using any CRO to view this signal... so my circuit should do the entire operation.

is this possible???

 

[akg]

since you are talking about any signal . Then you have to implement it in the DSP domain. take the FFT .

 

[raviram87]

sir.... since i am a second year undergrad student, i have just begun the process of learning DSP... i do not have any idea about implementations in the DSP domain.... sir, are such circuits not possible with normal electronic components say such as opamps, comparators etc???

 

[raviram87]

sir i am new to this concept of PLL... after you suggested i read about it... and i know the basics now.... can you please explain in detail as to how a PLL will help in my project??? please!!! or do mention some websites or books that i can refer to!!! please

 

[Roff]

If you can specify frequency and amplitude ranges (minimum, maximum), someone here can probably help you.

 

[demokesola]

are you displaying the frequency with LCD, 7-seg, or diodes(calibrated)... You'ld need to know the max. and min frequencies your ckt can accomodate

 

[Russlk]

If you rectify and filter, the frequency is easy to measure:

 

[raviram87]

sir.... thank u for the circuit.... once i get the output waveform how do i measure the frequency??? i will not be viewing it on the cro also.... and more over i wish to display the period of the wave on a 7 segment display unit!! how can i do that???

sir... i am sorry if am annoying you.... since i am a new comer to electronics, i seek your help..... thank u....

 

[Roff]

If you rectify and filter, the frequency is easy to measure:

You know what they say about great minds.
That's the reason I asked about frequencies and amplitudes.

 

[raviram87]

hello sir.... in the circuit that you have given me.... what does that V1 represent???

 

[akg]

If you rectify and filter, the frequency is easy to measure:

but how can it get the 'fundamental' freq w/o freq analysis?

 

[raviram87]

i want my circuit to measure frequencies from say 100Hz to 10KHz..... and the amplitude levels of the input signal are +5V and -5V.....