Hello guys

I have an old training kits for FM and FSK modulation and demodulation experiments.
These kits are missing the 566 IC's, and both of their demodulation circuits are based on LM565.
I did try and ordered from a couple from different sources, but unfortunately all were fake.

I was wondering what would you guys advise to get these kits running again.

FM modulation:

FSK modulation:

 

Try a CD4046 or 74HC4046

 

FM modulation:

That circuit needs some resistance in series with the DC input, otherwise that input will short the Audio input signal to ground.

 

The CD4046 as old as it is, it is not as ancient as the 566 and therefore still widely available.
EDIT, additionally because the 4046 already has a frequency offset provision, the FSK circuit is greatly simplified, one only requires to inject the 0 and 1 directly to the VCO input.

 

The CD4046 as old as it is, it is not as ancient as the 566 and therefore still widely available.
EDIT, additionally because the 4046 already has a frequency offset provision, the FSK circuit is greatly simplified, one only requires to inject the 0 and 1 directly to the VCO input.

INDEED!! I did find the LM566 in my 1978 National Semiconductor book. The 4046 certainly is a better choice.
I am wondering why the T chose the LM566. I suspect that it is no longer available, but maybe it was in stock somewhere.

 

Well he did mention ;
“I have an OLD training kits for FM and FSK”

 

Thank you guys.
I have found some schematics for the mentioned based on the 74HC4046. And I would like to know what you guys think.

FM Modulation:

FM Demodulation:

FSK modulation:

FSK demodulation:

 

It's got to be a really low frequency FM signal it if can get through a 741!

 

It's got to be a really low frequency FM signal it if can get through a 741!

I guess so, it is just for experimentation and proof of concept..

 

A 741 will be very limited with a supply of only +/-5v. Use at least 12 or preferably 15 volts.
Same with the PLL itself. It does work, but linearity and range will be constrained with 5 volts, again use either 12 or 15v.
Additionally; although I don’t have access to the data sheet, if I recall correctly pin 10 is an open source, which requires a 10k or higher resistor to ground.

 

@Shamoooot
dont know where you are based ,
but
as far as I can see the texas instruments TLC556, is in production , pin fit , and available ( at price) from distributeres such as cpc.farnell.com

 

@Shamoooot
dont know where you are based ,
but
as far as I can see the texas instruments TLC556, is in production , pin fit , and available ( at price) from distributeres such as cpc.farnell.com

Thank you. I think you mixed up between 556 and the required 566 ..

 

Thank you. I think you mixed up between 556 and the required 566 ..

My apologies, sorry , yes your right !

 

@Shamoooot
dont know where you are based ,
but
as far as I can see the texas instruments TLC556, is in production , pin fit , and available ( at price) from distributeres such as cpc.farnell.com

 

This chip is long obsolete

 

a suitable replacement is the LM331 which is still in production but will need circuit modifications to use it

 

The 556 is a dual timer, equal to two type 555 timer ICs. The CD4046 is a PLL IC with an internal voltage controlled oscillator. It is good for quite a few MEGAHERTZ. In addition, it can operate on either 5 volts or 12 volts very well. There may be some issues at 3.3 volts, depending on the device manufacturer. AND CERTAINLY you do not want to use a 741 op-amp. They are antiques.

 

Hello again
I was trying to simulate the circuits but seems like there's a problem in the output stage that I can't figure out.
I attached the Proteus project file if someone could take a look at it.
Project

 

I think that if the TS writes out a DETAILED DESCRIPTION of the operation of the last section of the circuit, that the problem will become clear. (Asking for a detailed description is my common trick for bringing out problems with ideas.)
I do see what look to me like problems.

 

I think that if the TS writes out a DETAILED DESCRIPTION of the operation of the last section of the circuit, that the problem will become clear. (Asking for a detailed description is my common trick for bringing out problems with ideas.)
I do see what look to me like problems.

The final stages for the demodulation parts are:
-Low pass filter for the FM.
-Comparator for the FSK.
If that what you meant.