A regular PLL could probably detect two signals, but the problem is that when the frequency of the two signals are the same, the output does not stay the same. This can be because both square wave signals are not in sync (Like square wave A is rising about 1 second sooner than square wave b). The reason why I want to use a 555 is because I want to reset it so that I can shift the wave and eventually have wave A rise at the same time as wave B.

Here is an example. Say I started the local clock, and the remote clock (that is to be compared with the local one) starts 1/2 a second later. If both run at 1Hz, the PLL's output will not stay the same all the time. I want to somehow obtain the same output, just because the frequencies are the same.

I think either Resetting the 555 or triggering it will help.

I'll give you a diagram of what I am trying to achieve if you need it.

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The CD4046 using the type 1 phase detector (XOR) maintains a 90 degree phase angle but you can get an in phase signal with a divide by 4 Johnson counter. You will need several CD4046 to cover the frequency range, or perhaps a frequency detector and switch to change range.

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Aren't you using frequency-shift-keying so the higher frequency is a logic high and the lower frequency is a logic low? Like an old-fashioned modem.
Then frequency is important, not phase nor sync. Also, then you don't need a clock in the receiver.

What is the nonsence about using a clock frequency of only 1Hz?

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I don't think he's ever mentioned what he's trying to do?, however, as usual, it's probably complete nonsense?.

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I will show you a diagram to avoid all confusions. (see attachment)

The diagram is divided into 2 groups. A and B.

Group A shows completely equal waveforms in every aspect from two oscillators.

Group B shows waveforms of the same frequency, but they are not in sync.

Now here is my request in the simplest terms:

I want to make a circuit that has two inputs and one output. The inputs will be the waveforms coming from each oscillator. The output will be a logic high if the oscillators produce the waveforms like group A (everything synchronized). The output will be a logic low if nothing is in sync. For example, group B.

A PLL will not work for this task because the output oscillates when the inputs to it are equivalent to group B.

Do you get what I am saying yet?

It's more like a wave matching circuit, that works better than a PLL.

Attached Images

wf_930.gif (465 Bytes, 304 views)

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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.

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

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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.

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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.

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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.

That is what I have coming out of the transmitter.

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

This is the part I need help implementing.

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

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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?

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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:

 

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.

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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?

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Yes

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.

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