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LM567 decoder

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freddy_uk

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is it possible to get a single LM567 chip to detect tones between 500hz and 3000hz?

if so how do i work out the values of the resistors and capactiors required??

thanks
 
The datasheet says the maximum detection bandwidth is 10% of center frequency. If your center frequency is 1.2kHz (geometric mean of 500 and 3000), then the maximum bandwidth you can get will be 120Hz. It won't work.
Why do you think you need a filter before your detection circuitry?
 
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The datasheet says the maximum detection bandwidth is 10% of center frequency. If your center frequency is 1.2kHz (geometric mean of 500 and 3000), then the maximum bandwidth you can get will be 120Hz. It won't work.
Why do you think you need a filter before your detection circuitry?

may be i dont need a filter, how would i cover the full bandwidth 500hz to 3000hz, is there another chip more suitable??
 
What do you mean cover?

Do you need an amplifier?

If so what gain?

What power output?

Load impedance?

Does it matter if it amplifies other frequencies as well?

What's wrong with a simple op-amp?
 
Hi Freddy.

What is your end application for such frequency detection? If you're after a sharp cut-off frequency for your detector, it could be tough. An extreme solution would be to use the 567 with an analogue switch or digital pot to sweep the center frequency across 500 to 3000Hz, and a latch on the output to detect any output pulses. But its response would be slow.

There may be other solutions using a 555 timer as a sort of pseudo missing pulse detector. But as I said it really depends on what you are using this for.

Blueteeth
 
Can we please see the bigger picture?

Why do you want to do this?
 
Freddy has 3 separate threads on this same topic. :eek:

Freddy, I hope you realize that was a bad idea.:(

If you are trying to detect the presence of signals on a phone line, I don't think it will support frequencies much outside the 500Hz-3kHz range. You shouldn't have a problem unless you get interference from the mains, which I suppose is a possibility, depending on where you place your inductive pickup and how much bandwidth it has.
 
Creating multiple threads is a bad idea.

Multiple threads do not increase your chance of a helpful response but only reduce it, as people get confused and can't always see what others have suggested in the other thread(s).

I'm through with this, I'm not going to bother trying to keep track of the numerous threads, I'll just ignore them.
 
Hi Freddy.

What is your end application for such frequency detection? If you're after a sharp cut-off frequency for your detector, it could be tough. An extreme solution would be to use the 567 with an analogue switch or digital pot to sweep the center frequency across 500 to 3000Hz, and a latch on the output to detect any output pulses. But its response would be slow.

There may be other solutions using a 555 timer as a sort of pseudo missing pulse detector. But as I said it really depends on what you are using this for.

Blueteeth


thats blueteeth, i dont require such a sharp cut off im jst tryin to only detect the tones present on the cable and no interferance, are you reffering to the lm567, ive been told its obselete now.

its to test any audio cable, i dont want to make contact with the conductors

thats for keepin withit i will not make anymore theads on this, i just thought previous theads were goin no further.

thanks for your replys
 
is it possible to get a single LM567 chip to detect tones between 500hz and 3000hz?
Detecting tones in such a wide range will be VERY prone to falsing on noise and will trigger on any voice traffic.
If you still want to do this you could cascade multipole filters, one 500Hz highpass and one 3Khz lowpass, followed by a simple diode detector.
Now if you are just trying to detect two tones, 500Hz and 3Khz, then a reliable detector can be made with just two LM567s and some simple logic.
 
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So this is about testing audio cables, and looking at their frequency response? Is this in system? Or can you build a box where you plug in each end to check? I'm afriad my telecoms knowledge is sparse so I need more info.

kchristie made several good points. :) But he idea of a bandpass filter, with a diode detector is probably your best bet for covering the entire range. Also, adding a comparator on the end would be useful in adjusting the sensitivity of the circuit. Enough to prevent false triggering at least.

If you want to see the complete frequency response a pseudo spectrum analyzer might do, using a frequency sweeped oscillator but you'll need to be able to put a specific signal into the cable and listen to it at the other end. I'm just spouting idea's here.

Blueteeth
 
Detecting tones in such a wide range will be VERY prone to falsing on noise and will trigger on any voice traffic.
If you still want to do this you could cascade multipole filters, one 500Hz highpass and one 3Khz lowpass, followed by a simple diode detector.
Now if you are just trying to detect two tones, 500Hz and 3Khz, then a reliable detector can be made with just two LM567s and some simple logic.

sounds ideal, just what i need, but where do i start, can anyone help with circuit diagrams and values of components, its been a while since ive done anything like this and i dont really know what to do next

thanks for your replys
 
hi freddy,
Would detecting any frequency between 500Hz and 3Khz be acceptable.?

In other words if a frequency was detected between these limits a 'detect flag/bit' or 'alarm' was given
OR
do you need to know the frequency being detected.?
 
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hi freddy,
Would detecting any frequency between 500Hz and 3Khz be acceptable.?

In other words if a frequency was detected between these limits a 'detect flag/bit' or 'alarm' was given
OR
do you need to know the frequency being detected.?

thanks for the reply, don't need to know the freqency...
what ideas have you got?

thanks
fred
 
sounds ideal, just what i need, but where do i start, can anyone help with circuit diagrams and values of components, its been a while since ive done anything like this and i dont really know what to do next
Here is a link to some software for designing the filters:
Active Filter Design Application - FILTERPRO - TI Software Folder
The more poles you add to the filters, the steeper the skirt becomes.
To design the rest of the circuit, you need to know the min/max voltage level of the tones you want to detect and how long you want the LED to be on after detecting tones.
 
thanks for the reply, don't need to know the freqency...
what ideas have you got?

thanks
fred

hi freddy,
Its possible to use monostables and gates to give out a 'logic signal' when a frequency is within set limits.
 
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