4046

A PLL will decode pure tones. To use the 4046 you'll have to square up the audio into a logic signal. Once you've done that set up the 4046 to lock on the tone of interest, use the VCO drive as a frequency reading and (if it's pure enough) the lock pulses to tell you if the tone is really there.

Having said that, there are probably _much_ better ways of doing this, particularly since you could probably do some DSP Lite in some little microprocessor.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Amazed to see it still exists...decades ago I built telex and morse decoders with it, using the same oscillator in the 567 to generate telex / morse signals.

(dreams of using the Commodore 64 to decode funny agressive anti-capitalist Russian propaganda telex...damn - I get old)

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 - René

Heh...my C64 is sitting on the shelf only a few feet away. Used it for the same things and controlling a DX440 : )

The XOR phase detector will work with a fair amount of noise. You need to prevent huge spikes from getting to the PLL chip so there is likely to be a resistor in the input signal path. You will also need a capacitor in series to allow the PLL input to self bias.

Vcc ! --- 1N914 ^ ! 2.2nF ! --/\\/\\---+--+-------+-----!!----! Sig in 22K ! ! ! --- --- 1N914 ^ --- 22nF ! ! GND GND

You will want a counter chip so that the VCO output can be made to run at

4 times the 440Hz input. Assuming there is enough noise, you can decode the "I'm locked" signal with a quad XOR gate chip.

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kensmith@rahul.net   forging knowledge

No, the 4046 will do the squaring up for you. You just need a capacitor to let is self bias.

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kensmith@rahul.net   forging knowledge

Yep!, the same dreams. Used the XR2211 demod chip. Vary, Baud, shift, damping, centreF. Components calculated on the Sinclair Spectrum then in turn programmed to do datastream to text. Then add inline audio notch filtering and amps. Move then onto communications receivers ... Happy days. Learnt a lot stuff but mainly the niceness of Z80 machine code and the need for fast, efficient programs. Won't throw the kit out as there's 6 months of my locked life in it :) john

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Oh, thanks... Can you help me qith the design ? What capacitor ? 220nF ?

See the ASCII art I did. Look at a 4046's data sheet. Do a bunch of calculations like:

F = 1 /(2 * PI * R * C) or C = 1 /(2 * PI * R * F)

You'll catch on.

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kensmith@rahul.net   forging knowledge