Frequency to Voltage con on sx28 ???

Gold_Daddy · 2007-02-09 02:40

Hi Everyone

·· I am looking for a way to input a·varying sine wave·frequency (from 5 Hz to 3000 Hz) and assign either a voltage or a number to it.· I would like to compare it to a table of pre-set frequencies and output an alert when certain frequencies are hit exactly.· I need to use an sx28 @ 50 Mhz.·

·· Would I need an ADC or an FVC·or can the sx28 handle the conversion?
·· Do I need to filter the signal to eliminate harmonic overtones and how can I do this?
········ (RC filters maybe???)

Any ideas or help with programing and hardware design would be greatly appreciated !

Gold_Daddy

Peter Verkaik · 2007-02-09 03:05

Here is an example of frequency detection
http://www.sxlist.com/techref/ubicom/lib/math/dsp/freqdet/index.htm

regards peter

Gold_Daddy · 2007-02-09 05:28

··· Peter --- Thank You·---· This will help!!!

· The only problem with the code you referenced; it is single ended.

· It only finds the amount of a single frequency chosen by the user.· I need the (program/hardware) to·differentiate between over a hundred different frequencies!·

Peter Verkaik · 2007-02-09 08:42

To detect varying frequencies a spectrum analyzer is needed.
See next article about an analyzer using a pic. This could possibly be·adapted
to a sx if you leave out the display code.
http://www.circuitcellar.com/library/print/0998/Lacoste98/lacoste98.pdf

Here is the pic source code for the·above article.
ftp://ftp.circuitcellar.com/pub/Circuit_Cellar/1998/Issue_98/
download picspectrum.zip

The·code is also interesting for just the math (FFT,sin.logarithm,fixedpoint)!

regards peter

Bean · 2007-02-09 12:07

Are you inputting a single frequency or multiple frequencies ?

If it's a single frequency, then I would just use the Schmitt trigger option for the input pin and time the pulse.

FreqIn  PIN RB.0 INPUT SCHMITT
 
cnt     VAR WORD ' Holds period in 2.56uSec; freq = 1/(cnt * 0.00000512); cnt = 65 = 3004Hz; cnt = 39062 = 5.0001Hz
 
 
' Clear period counter
cnt = 0
 
' Wait for input to go low
DO
LOOP UNTIL FreqIn = 0
 
' Wait for input to go high
DO
LOOP UNTIL FreqIn = 1
 
' Increase period counter while input is high
DO
  PAUSEUS 2.56 ' Tweak this value down to account for program overhead
  INC cnt
  IF cnt = $FFFF THEN EXIT ' Abort if counter is at max
LOOP UNTIL FreqIn = 0

Bean

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Cheap used 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com
SX-Video Display Modules www.sxvm.com
Stuff I'm selling on ebay http://search.ebay.com/_W0QQsassZhittconsultingQQhtZ-1

"USA Today has come out with a new survey - apparently, three out of every four people make up 75% of the population." - David Letterman

Post Edited (Bean (Hitt Consulting)) : 2/9/2007 12:19:44 PM GMT

Gold_Daddy · 2007-02-10 21:52

······ DON'T YOU GUYS EVER SLEEP ? ! ? !
·
· Like I should talk

····· Peter;· Thank you again for your input

·HOW DO YOU FIND THIS STUFF?·
I haven't had a chance to go over the links you refer to, but they sound very helpfull!

······ Bean;· Think of the source as a violin played by a beginner (my daughter is learning

·)· The sine waves vary from moment to moment but they may not be true to notes desired.· Similarly, I am trying to determine when a stream of varying waves hit certain frequencies but I only have to denote when the frequency matches/ or does not match, a set of predetermined frequencies.· I would be happy with a green led for hit and a red led for not true to data set.

Thanks again,·I'll need some time to absorb the files you mentioned

Peter Verkaik · 2007-02-10 23:09

To find stuff for the sx, you should always include pic.
I just googled for pic spectrum analyzer

regards peter

Frequency to Voltage con on sx28 ???

Comments