band pass filter

[javed007>co>uk]

As part of my final year project i need to detect only 1 of 4 transmitted frequencies at any one time. The four frequencies are 300 Hz, 600 Hz, 1200 Hz and 2400 Hz. Depending on which frequency is detected, a different output occurs. The problem i have is which is the best method of detecting these frequencies but bearing in mind that these frequencies are to be transmitted along telephone cable. I know that only frequencies up to about 3200 Hz may be transmitted along telephone cable. I have looked at bandpass filters but i am running out of time and i am having technical diffculties with single op-amp based band pass filter circuits i have used. Is anyone able to offer a solution to these problems that would be doable?
Thankyou.

 

[crust]

How are you supposed to do it? Analog parts? Using a micro? a PC? You could build a set of filters, 2 bandpass, a low pass, and a high pass? You could do a _very_ easy modified FFT in software (since you know the frequencies, you dont need to compute the whole thing). You could use three high pass filters, then use logic to deduce which signal showed up ...

there are lots of solutions to this problem ... please post some more information about how you plan to do it, what you are supposed to use, etc.

 

[Nigel Goodwin]

Have you considered using LM567 PLL chips?, these work as tone detectors, you just need to wire four of them up from a common input, and have each one tuned to a different frequency.

 

[mozikluv]

filter

hi,

how about a tunable variable filter

 

[javed007>co>uk]

thanx guys it helped