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frequency converter circuit

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Mridu

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Hi all,
i am doing a biomedical project on breath analysis.........i need to change my 1.5Hz breath signal to about 200hz inorder to give as input to the soundcard
how to design such a frequency to frequency converter circuit?
 

matthai

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Hi,
you have some missing parameters,
please specify waveform?,square,sin etc.
we can use two methods
using PLL & frequency doubler using gates

best wishes,
matthai
 

andre_teprom

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The sugestion above could fit your need with a LM565 IC .
However, if you intend to change the beep sound proportional to hartbeat, a more precise way could be achieved using a very small uC.

No need of timer-capture module and D/A module, but just an 2 order RC filter.

+++
 

Mridu

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Hi matthai,
my waveform is random signal..............it is the actual breath signal..........it mainly appears as a pulse.....i need to change frequency from 1.5 Hz to about 200Hz.............can i do this with a pll how to i design it?
 

andre_teprom

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Taking a more accurate analysis, now I don´t believe that a PLL could solve this problem anymomre.
It is because PLL circuits needs a relativelly stable input frequency, and it must fit into a small variance range.

Think about microprocontroled sugestion above.
I already used that at ECG monitoring equipment.

+++
 

jpanhalt

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I am not clear on your question. Are you counting respirations? If so, 1.5 Hz is quite high (90 respirations per minute). A normal rate might be closer to 0.3 Hz (i.e., 18 to 20 per minute).

If you are talking about respiration sounds, I suspect there are some very low frequency ones. I don't know what the lowest measurable frequency for them is, but certainly physicians do not rely on anything below the audible range in normal physical diagnosis.

Can you clarify what your project is intended to do?

John
 

andre_teprom

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1,5Hz to 200Hz is compatible with BPM rate.
I assumed it based on the range above.

+++
 

Mridu

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Hi andre.......

so what you are suggesting is that i could use a micro-controller program for changing the frequency..........i can do that in pic16f877A right?
@john.....what i am observing in dso is my breath sound .............from my nose......it seems as a pulse..........
 

jpanhalt

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1,5Hz to 200Hz is compatible with BPM rate.
I assumed it based on the range above.

+++
What is BPM? Do you mean breaths per minute? Wouldn't a breath rate of 1.5Hz (if that is the correct unit) equate to 90 breaths per minute?

Normal respiratory rate in adults is usually less than 20 breaths per minute (Respiratory rate - Wikipedia, the free encyclopedia). 90 breaths per minute would be unhealthy, if continued for a long time. Such panting can lead to excessive loss of CO2 and respiratory alkalosis.

@Mridu
My question had to do with whether you were trying to distinguish the various sounds made when breathing as a diagnostic measure -- which is usually done by listening to the chest with a stethoscope -- or whether you are just counting breaths. Since you mention the noises from your nose, I assume it is just for monitoring the number of breaths. What are you using to pick up the sounds? If the device is for other people too, have you considered that not everyone breaths through his nose all the time.

Have you considered another technology, such as measuring the temperature change of a heated wire, which would depend on whether air was flowing over it or not, or CO2 concentration? I assume you have decided against physical methods, such as sensors around the chest.

John
 

andre_teprom

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What is BPM? Do you mean breaths per minute?..
John, sorry for do not clarify. I meant "beat" of heart ( that acronym is usual in my country )

Hi andre.......

so what you are suggesting is that i could use a micro-controller program for changing the frequency..........i can do that in pic16f877A right?
Exactly

+++
 

Mridu

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hi andre,

can u give ur sample program that u did in microcontroller...........my problem is my frequency being in such a low range........i think i have to add zeros into the wave inorder to make it 200 HZ.......is that possible?
 

BradtheRad

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About the closest thing to what you want would be to modulate a 200 Hz sine wave. You could use amplitude modulation, or frequency modulation.

With AM you would vary the intensity of the 200 Hz tone between, say 0.1 V to 1 V in the period of one breath.

With FM you would vary the frequency. This method is more involved than AM. The range needn't be only 199 to 201 Hz. It could be 190-210, or 180-220, etc.

It's still not clear what your 1.5 Hz signal is. Is it a single pulse at a particular moment of exhale or inhale?

Is it a gradually changing voltage? AC? DC? Is it pulse width modulated? Etc.
 

Mridu

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Hi brad...........my signal is like pulse at the moment of inhalation/exhalation.......it is bipolar and like AC..........so is FM advisable/should i implement in microcontroller?
 

betwixt

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Assuming it's the audio frequency spectrum you are trying to analyze, you could try using the audio to modulate a low frequency oscillator (say 1MHz) then listen on a domestic FM radio to one of it's harmonics. The modulating frequency will increase along with the carrier.

As you are dealing with very low frequency signals I would have thought a simple ADC would be the easiest way though. Even the cheapest microcontrollers can take hundreds of samples per second and store them in memory. From there you can either directly analyze the samples or transfer them to a PC as a WAV file and manipulate them with Audacity or a similar program.

Brian.
 

BradtheRad

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Hi brad...........my signal is like pulse at the moment of inhalation/exhalation.......it is bipolar and like AC..........so is FM advisable/should i implement in microcontroller?
Since you intend to send audio to your soundcard, it would be simplest to turn on a 200 Hz oscillator only during the positive section of your pulse. Or else to increase the volume.

That would be the AM method. The change in waveform would be obvious as you examine it with sound processing software.

To use FM you would produce 200 Hz during the positive cycle, then a different frequency during the negative part. The amplitude would not change.

As to which is better, it would pay to experiment with both AM and FM to determine which works best for your purposes.
 

andre_teprom

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hi andre,
can u give ur sample program that u did in microcontroller...
It was done in assembly for Z84 microprocessor.

The application were a little bit different from your.
The SPO2 value were subtracted from Timer, according specific algebraic rule, in order to modulate ECG beat in an audible sounds to speaker, wich determines if occured some change at that parameter, without need to nurse keep looking everytime displayed value.

+++
 

matthai

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hi mridu,

if you only intended to give this signal to sound card ,then you only need a 555 ckt to make that.
you only need to design a 200hz astble & give pin 5 to your signal,then you will get 200hz modulated with 1.5hz
you can also input this to uc.

matthai.
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Mridu

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Hi brian.........
i had same idea as this before but do not have time to implement this...and also i thought it as making the whole thing is more complex......simply giving to the sound card is far more easier.............
 
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