555 as a PLL?

audioguru · Dec 18, 2005

The oscillators won't have exactly the same frequency, so their periods also won't be the same. Therefore when they are sync'd, their gated output will have the difference and cause a logic low when you don't want it.

The phase detector in a PLL will give an output (or invert it if you want) when their frequencies are close enough, regardless of their phase.

Nigel Goodwin · Dec 18, 2005

mstechca said:
Do you get what I am saying yet?

Yes, but WHAT are you trying to do it for?.

mstechca · Dec 18, 2005

Nigel Goodwin said:
Yes, but WHAT are you trying to do it for?.

I have a transmitter that produces random pulses to my receiver.
I want the receiver to produce a logic high output when the pulses are received. If anything different is received, the output will be low.

Nigel Goodwin · Dec 18, 2005

mstechca said:
Nigel Goodwin said:

Yes, but WHAT are you trying to do it for?.

Click to expand...

I have a transmitter that produces random pulses to my receiver.
I want the receiver to produce a logic high output when the pulses are received. If anything different is received, the output will be low.

If the pulses are 'random', then by definition you can't distinguish them from anything else!.

What you need is a simple tone transmitted, and a PLL tone detector in the receiver (set to the same frequency) - when it receives the tone the PLL sets the output, when it doesn't receive the tone it doesn't set the output.

However, this crude type of signalling ISN'T terribly reliable, random noise could easily trigger it - it's more common these days to use a digital code with suitable modulation schemes.

mstechca · Dec 18, 2005

If the pulses are 'random', then by definition you can't distinguish them from anything else!.

And that is when I want a PLL to produce a logic low output. If the pulses are equivalent to what comes from the transmitter (a constant pulse running at one frequency), then I want a PLL to produce a logic high output.

What you need is a simple tone transmitted,

That is what I have coming out of the transmitter.

and a PLL tone detector in the receiver (set to the same frequency)

I can generate a tone at the same frequency with a 555 timer.

- when it receives the tone the PLL sets the output, when it doesn't receive the tone it doesn't set the output.

This is the part I need help implementing.

However, this crude type of signalling ISN'T terribly reliable, random noise could easily trigger it.

That shouldn't matter unless the random noise is the same signal.

Russlk · Dec 18, 2005

Let's see if I understand: The transmitter puts out noise until something happens to produce a constant tone. The circuit output should be high when noise is received and low when the tone is recieved. Correct?

akg · Dec 18, 2005

And that is when I want a PLL to produce a logic low output. If the pulses are equivalent to what comes from the transmitter (a constant pulse running at one frequency), then I want a PLL to produce a logic high output.

if the tone duration(which u require to decode) is long enough(ref the manul) , then a pll like 567 ( or others explained above) can produce the reqd o/p, and these pll have internal vco , so why use external 555??.. also if u require to decode only a limited nof separate tones , then using plls listed above is the low cost soln:

mstechca · Dec 19, 2005

Russlk said:
The transmitter puts out noise until something happens to produce a constant tone...

No

The transmitter puts out a continuous tone, and the tone never changes.

The receiver gives a logic high output if it can detect that the transmitter is sending the correct tone.

Russlk · Dec 19, 2005

OK, the transmitter puts out a continuous tone but sometimes the receiver is not able to detect it, and in that case you want an output of zero (if I remember correctly)? Why do you want a 1Hz to 1 kHz range? Does the transmitted tone change frequency?

mstechca · Dec 20, 2005

Russlk said:
OK, the transmitter puts out a continuous tone but sometimes the receiver is not able to detect it, and in that case you want an output of zero (if I remember correctly)?

Yes

Why do you want a 1Hz to 1 kHz range? Does the transmitted tone change frequency?

This will be the range of frequencies I will be experiementing with on the transmitter. I want the fastest detection with the lowest priced, and fewest components.

Nigel Goodwin · Dec 20, 2005

As previously mentioned you want an NE567 tone detector PLL IC - simple to use, and does just what you need.

mstechca · Dec 20, 2005

Nigel Goodwin said:
As previously mentioned you want an NE567 tone detector PLL IC - simple to use, and does just what you need.

I'll try it then. thanks.

Russlk · Dec 20, 2005

You will need several 567s to cover the range. I worked up a design using the CD4046, it takes 3 circuits to cover the range of 1 hz to 1kHz. If you build it, please let me know how well it works. Oops I forgot, use a coupling capacitor to pin 14 unless the signal is logic level.

akg · Dec 20, 2005

i was wondering that, is (s)he is trying to cover the entire range of 1hz to 1K using PLL(s)!!

Nigel Goodwin · Dec 21, 2005

akg said:
i was wondering that, is (s)he is trying to cover the entire range of 1hz to 1K using PLL(s)!!

No, he's only wanting to detect a single frequency, either ON or OFF, the (rather silly) range he specified was only so he could try for the optimum frequency.

akg · Dec 21, 2005

hmmm....

" You will need several 567s to cover the range. I worked up a design using the CD4046, it takes 3 circuits to cover the range of 1 hz to 1kHz. ""..

this comment inspired me to think like that..

Gaddy · Jun 2, 2008

It is possible

yes you can make a pll with a 555, but i doubt that in the frec that you want to, thas was my first desing of pll, a xor gate, a low pass, an amplifier, an that was done, i was quite amazed, was in lock even when they have differen duty cycles, in this case you may do it, digitally, with a rate of meassure, with a computer, example if you want to buil a tacometer.

Gaddy Alcalà

Gaddy · Jun 2, 2008

with a PIC, maybe 1hz is too much

slifer88 · May 3, 2009

cant find 4046 in orcad 9.2 i need it for the simulation..plz help

555 as a PLL?

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