frequency feed through MUX

[amitaiwe]

Hi to all,
I'm trying to build an oscillator (frequency of ~400hz) using a LC tank and I have a few questions connected:
1. Is it possible to do that when one leg of the LC tank (a parallel one) is wired through a MUX (a TC74HC4051 analog 8 to 1 bidirectional )?
The frequency is supposed to be oscillated using a 555 timer.
2. will the same be for a shift register? Is the SR suitable only for digital bus or that it can
be fed with an analog signals?
Thanks, Amitai

 

[Audioguru]

You forgot to post the schematic of your 555 somehow driving an LC tank.

A MUX works with analog or digital signals.
A shift register is digital only.

 

[amitaiwe]

Thanks for the quick answers.
I tried to draw an idea of a schematic for the circuit:

Amitai

 

[Audioguru]

The input and outputs of a Cmos MUX must be able to swing up and down within the power supply voltage. Since your inductors connect to ground then the outputs that drive the inductors must be able to swing positive and negative which is impossible with a single positive supply voltage.

Your circuit does not make sense since an LC is a resonant high impedance but the MUX and maybe your signal source are low impedances.
Why do you have TWO LC tanks?

Nobody uses an LC to make an audio oscillator, it is used to make a radio frequency oscillator. You should use a Wien bridge, phase-shift or Bubba oscillator instead.

 

[amitaiwe]

Thanks Audioguru,
I didn't understand a few things in your answer:

Can you explain whats the high-low impedance problem exactly?
you mean that it's not effective enough and to mach energy is lost, or
that no current will pass throw in such design?

You have mentioned the oscillator types because that I mentioned the 400hz frequency?
I am told to use in the mean time only an LC tank oscillator and I have successfully build up one
without the MUX in between.

Is there any way to overcome these problems which you have mentioned?

For now I can't be more specific and give more details about
the project, I hope i will be able soon enough.
Thanks again,
Amitai

 

[Audioguru]

1) Can you explain whats the high-low impedance problem exactly?
you mean that it's not effective enough and to mach energy is lost, or
that no current will pass throw in such design?

An LC tank at resonance is a high impedance that needs a high impedance source and load. Your simple circuit has no load.
If the input of the MUX is connected to the output of a 555 squarewave oscillator then the 555 output impedance is so low that the tank will not do anything.

You have mentioned the oscillator types because that I mentioned the 400hz frequency?

The circuits I mentioned make good sinewave audio oscillators. Your 555 makes a squarewave and an LC tank is used in a radio frequency circuit.

I am told to use in the mean time only an LC tank oscillator and I have successfully build up one
without the MUX in between.

Please post your schematic of a 555 driving an LC tank.