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Electronics => Electronics => Topic started by: 555 timer chip guy on March 20, 2007, 05:40:01 PM

Title: Recognizeing a frequency
Post by: 555 timer chip guy on March 20, 2007, 05:40:01 PM
Dos any one have a circuit that can recognize a specific frequency.
Title: Re: Recognizeing a frequency
Post by: Kohanbash on March 20, 2007, 07:44:42 PM
do a google search for a notch filter or bandpass filter.
you can use an op amp or a simple RLC circuit.
Title: Re: Recognizeing a frequency
Post by: robot321 on March 20, 2007, 07:48:49 PM
the G8870 decodes DTMF Freqs.
Title: Re: Recognizeing a frequency
Post by: 555 timer chip guy on March 21, 2007, 01:37:41 PM
It needs to be able to recognize square wave forms.
Title: Re: Recognizeing a frequency
Post by: Kohanbash on March 21, 2007, 08:15:44 PM
maybe a DAC before the notch filter. Or use a cap in parallel with the receiver to convert to sinusoidal. I don't know of any offhand but they make tone decoder IC's which also might work
Title: Re: Recognizeing a frequency
Post by: trigger on March 21, 2007, 08:42:40 PM
why don't you ADC your signal, and then filter in software? (e.g., use DSP).  Much easier to find a square wave. 
Title: Re: Recognizeing a frequency
Post by: 555 timer chip guy on March 22, 2007, 02:06:12 PM
thanks but I don't know how to do that yet. :(
Title: Re: Recognizeing a frequency
Post by: Kohanbash on March 22, 2007, 03:01:30 PM
You will need to play with the values a lot but here is a basic circuit that should work.
Title: Re: Recognizeing a frequency
Post by: 555 timer chip guy on March 24, 2007, 09:13:50 AM
You will need to play with the values a lot but here is a basic circuit that should work.
Thanks for that schematic I was looking at some thing very similar a littel wile ago
do you haze any basic starting values I could use for maybe 100Hz , and also I heard you could use a comparator and a crystal to recognize a frequency.
Title: Re: Recognizeing a frequency
Post by: ed1380 on March 24, 2007, 09:18:53 AM
<-noob
Isn't that what an osciliascope is for?
Title: Re: Recognizeing a frequency
Post by: zamboniman60 on March 25, 2007, 06:26:28 PM
well, if you don't have an extra $160 laying around for an oscillosope, you could use the "inductor in series with an LED brightness test" or the "speaker and function generator guesstimation".