FREQUENCY TO VOLTAGE CONVERTER using ADC?

i have a certain sine wave input in the 480 khz range.i would like to
make a pseudo frequency to voltge converter by using the ADC of my
pic16lf876a..

any reaction?is this possible?

thanks!

> i have a certain sine wave input in the 480 khz range.i would like to
> make a pseudo frequency to voltge converter by using the ADC of my
> pic16lf876a..
>
> any reaction?is this possible?

Yes it's possible.  Depending on numerous unstated requirements, using
an ADC might be overkill.

JJS

thanks..
assuming an 8-bit resolution,how will it relate to my input freuquency?

my application is a metal detector. i have an lc tuned copitss
oscillator where my loop antenna acts as my variable inductance..the
common practice is beating this with a certain frequency and extract
the difference..
for my part, i would like simply to have some ways to translate the
frequecny change in to a voltage change the simplest way.i tried f>v
converter but they have low frequency input...

"electro" <electromagnetic377@yahoo.com> wrote in message 
news:1144334524.180706.50700@t31g2000cwb.googlegroups.com...
>i have a certain sine wave input in the 480 khz range.i would like to
> make a pseudo frequency to voltge converter by using the ADC of my
> pic16lf876a..
>
> any reaction?is this possible?
>
> thanks!
>
You can use the ADC if you put a frequency to voltage converter in front of 
it. What I'd use is a phase lock loop.

Or just run the signal through a signal conditioner and comparator into an 
interrupt pin and measure the wave period. If you count a decent number of 
cycles over a fixed time period you should be able to get your frequency 
measured as accurate as you want.

Peter 

"electro" <electromagnetic377@yahoo.com> wrote in message
news:1144335447.002808.28420@v46g2000cwv.googlegroups.com...
> thanks..
> assuming an 8-bit resolution,how will it relate to my input freuquency?
>
> my application is a metal detector. i have an lc tuned copitss
> oscillator where my loop antenna acts as my variable inductance..the
> common practice is beating this with a certain frequency and extract
> the difference..
> for my part, i would like simply to have some ways to translate the
> frequecny change in to a voltage change the simplest way.i tried f>v
> converter but they have low frequency input...

And what do you want to do with the voltage? Drive a meter? produce a tone?
or use the signal in the digital domain. I suspect that just want the
frequency shift a a numerical value in which case feeding the osc into a
counter sampled regularly to get a frequency number, then just subtract base
frequency. You could have a push-botton that tells the micro to take the
current measured frequency as the base. Just make sure the micro has a
stable clock source i.e use a crystal not an RC osc or ceramic resonator.

As for analog output - an DAC, PWM or counter driven square wave (for freq
out).

Peter

On 6 Apr 2006 07:42:04 -0700, the renowned "electro"
<electromagnetic377@yahoo.com> wrote:

>i have a certain sine wave input in the 480 khz range.i would like to
>make a pseudo frequency to voltge converter by using the ADC of my
>pic16lf876a..
>
>any reaction?is this possible?
>
>thanks!

Sure. For example, you could trigger a 1us monostable from the input
waveform, low-pass filter the CMOS output and feed that to your ADC.
Only a few parts, depending on the input amplitude. 



Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

i would like to use the voltage as an indication of a change in ambient
frequency due to a close metal...
my initial idea was to full rectif the sine wave signal and extract its
dc content...
but since i wil be using a pic with adc capabilities..im now looking
for ways to use that..
do i really need an interface between my instanteanous analog 478khz or
say 296khz sine wave and the ADC port of my pic?isnt it it is an analog
to digital converter?so why still need an interface?

thanks!

On 6 Apr 2006 08:55:41 -0700, the renowned "electro"
<electromagnetic377@yahoo.com> wrote:

>i would like to use the voltage as an indication of a change in ambient
>frequency due to a close metal...
>my initial idea was to full rectif the sine wave signal and extract its
>dc content...
>but since i wil be using a pic with adc capabilities..im now looking
>for ways to use that..
>do i really need an interface between my instanteanous analog 478khz or
>say 296khz sine wave and the ADC port of my pic?isnt it it is an analog
>to digital converter?so why still need an interface?
>
>thanks!

The ADC measures analog voltage, not frequency. Which do you want? 

You can also measure the frequency directly with a PIC using on-chip
counter/timer hardware, but I fear you are in well over your head on
this one. 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:
> On 6 Apr 2006 07:42:04 -0700, the renowned "electro"
><electromagnetic377@yahoo.com> wrote:
>
>>i have a certain sine wave input in the 480 khz range.i would like to
>>make a pseudo frequency to voltge converter by using the ADC of my
>>pic16lf876a..
>>
>>any reaction?is this possible?
>>
>>thanks!
>
> Sure. For example, you could trigger a 1us monostable from the input
> waveform, low-pass filter the CMOS output and feed that to your ADC.
> Only a few parts, depending on the input amplitude. 

Looking at some of his other posts on the topic I think it's critically
dependent on input aptitude, which I fear is low :-)

-- 
Nobby Anderson

electro wrote:
> i would like to use the voltage as an indication of a change in ambient
> frequency due to a close metal...
> my initial idea was to full rectif the sine wave signal and extract its
> dc content...
> but since i wil be using a pic with adc capabilities..im now looking
> for ways to use that..
> do i really need an interface between my instanteanous analog 478khz or
> say 296khz sine wave and the ADC port of my pic?isnt it it is an analog
> to digital converter?so why still need an interface?
>
> thanks!

The short answer to your question is that you need circuitry to provide
a proper electrical (signal) interface between the signal source and
the ADC.  The ADC has specific requirements of what it expects to be
driven with, and if these requirements are not met, you will get, at
best, erroneous results.

I agree that, based on some of the questions you are asking, it appears
that you are in over your head on at least some portions of this
design.  It happens even to the best sometimes.  You might, however,
wish to see if you can find a consultant who may be able to help you
along with some of the portions you are having trouble with.