Time Shift???

ok.... i would like to show to you one circuit that i got from a particular site.... it was a pitch detector.... but i did not understand how it works.... i understood the first part of the design.... that is the given waveform is converted to a square wave using an op-amp... but couldn understand after that.... can you explain the working of this circuit??? (we do not want to copy that idea, but if it works, we would like to do something similar to that...) i have attached the circuit for reference...

moreover when listening to FM radio, while tuning a particular station frequency, i have seen a LED glow up.... that means my circuit has latched on to the particular frequency rite?? how it works?? and is it of some relevance to my project???

Measuring the frequency of a single tone is relatively easy. Measuring the fundamental frequency of a signal that contains high-level harmonics, with an analog circuit, is extremely difficult if you have no defined bounds on the frequency and amplitude of the fundamental and the harmonics.
The scheme you are suggesting is a comb filter. If you could do this in analog fashion (e.g., using a CCD bucket brigade circuit), you would still have to deal with the fact that the output matches the input at time T, and 2T, and 3T, and ..., where T is the period of the fundamental frequency of your input.

if you look at my previous posts... we thought of this idea of shifting the given signal by small intervals of time and each time compare this time shifted signal with the original signal....

but how to shift the signal by some small amount of time??? are their any circuits or ICs that can do this?? and wether this idea will work???

I heard of TIME DELAY RELAYS...... is it of relevance to what i have discussed??? please help.... can i use them to shift the signal???

The problem you've got is that even if you could time shift the signal, how are you hoping to compare it? You'd need to compare a distinct time-slice of both signals, not the instantaneous value of both signals because otherwise you could easily get a false trigger that the waveforms are the same when infact they are not.

To my mind, the only way to compare a "time slice" of two signals is to digitise them both and do some maths on them. ie a microcontroller or a DSP, which you have already specified as not being allowed.

I think my earlier suggestion would be a better route to investigate, but it seems I was right to question whether my idea would work for complex waveforms. You'll need to research into breaking a signal down to it's fundamental - have a look at comb filters as RonH has suggested.

Brian

hey thanks brian.... you have been of great help to me.... can you please also explain how this idea of comb filter works??? or what does this comb filter do??? otherwise, please suggest me some sites that can help me out.....

and it is not that i cannot use a microcontroller.... the point is if i use a microcontroller or say i perform an analog to digital conversion at some point of my circuit i will lose more points, if some other team has come out with a better design....

but please do help me in digital domain as well.....

The obvious analogue solution as far as I can see is an oscilloscope.

JimB

I was thinking about that earlier JimB. An oscilloscope manages quite easily to determine the frequency of any signal, provided it's periodic. That's not to say that the circuit designs behind it are simple, but I wonder how it works? I've never looked into oscilloscope design before.

raviram87:

If you can do some research into how an oscilloscope works, you might well turn up a few ideas on how you can accomplish this with analog designs.

Brian

k guys.... let me go thru this oscilloscope, if i find the resources for the same... but plaese continue to post ur ideas as well....

raviram87 said:

hey thanks brian.... you have been of great help to me.... can you please also explain how this idea of comb filter works??? or what does this comb filter do??? otherwise, please suggest me some sites that can help me out.....

Click to expand...

If we can Google,you can Google.
Try "ccd bucket brigade" and "analog delay line".
Here are a couple of good hits:
**broken link removed**
http://www.geofex.com/sad1024.htm
I saw one price quoted: US $40.

and it is not that i cannot use a microcontroller.... the point is if i use a microcontroller or say i perform an analog to digital conversion at some point of my circuit i will lose more points, if some other team has come out with a better design....

but please do help me in digital domain as well.....

Click to expand...

hey thanks..... the links were of real help to me.... thank you so mcuh....

but can you also help me out with the FM tuning??? i.e, in my radio set, i have observed that as i tune and when i match a particular station frequency then a red LED glows up.... is it of some relevance to our project?

I'm afraid the SAD-1024 is too long for your application. The minimum delay is about 340 usec, which means your maximum fundamental frequency would be about 3 kHz. I don't believe you have said what range of frequencies you have to detect.

raviram87 said:

but can you also help me out with the FM tuning??? i.e, in my radio set, i have observed that as i tune and when i match a particular station frequency then a red LED glows up.... is it of some relevance to our project?

Click to expand...

No, it's merely a signal strength indicator.

the rules of the competition say that, the higher the frequency range i can measure, we get more points!!! but as you said we need a certain limit.... the minimum has been specified as 100Hz.... so if we are able to go up to a appreciable range in the KHz range, think it will be good!!