I need some project help.

[ChristianCMcKay]

So be gentle with me. I haven't been doing electronics for very long. Just about two years now at school and I've never really done anything that involved a PWM.

I want to start a project where I take the RCA output from the head unit in my car and change the signal to a pulse width modulated output into a fiber optic cable where it will then be converted back to analog RCA at the amp.

So I have quite a few questions, but I'm going to start with the first one. I know that for pulse width modulation, I will need a triangle wave. Can anyone tell me what frequency the oscillator will need to be? I would like for the frequency response to be between 10 Hz to 22 kHz (I want to go a little over what it needs). Any ideas on what oscillator circuit I should use for this?

 

[crutschow]

Just buy a analog-to-toslink converter and a toslink-to-analog converter. It's a lot easier, transmits stereo, and likely will work better than anything you could make.

If you want the fun(?) of making you own, then you will should use a pulse frequency of at least 5 times the highest frequency you want to transmit or 110kHz minimum.

Do you want to transmit a stereo signal? If so you will need two of everything.

 

[ChristianCMcKay]

I'm mostly wanting to do this for the fun. So would raising the oscillator frequency increase the number of samples per cycle?

I'm sorry, I just thought about that for a little while and realized that was a stupid question. Of course it does.

So would there be any disadvantage of using a significantly larger oscillator frequency frequency than 110 kHz?

 

[crutschow]

.....................
So would there be any disadvantage of using a significantly larger oscillator frequency frequency than 110 kHz?

The only problem is if you reach the frequency response limits of the circuits, such as the one generating the sawtooth or triangle wave. The flat part of the wave must be linear to minimize distortion in the modulated signal.

Otherwise a higher frequency is better since it minimizes the filter requirements at the receiver when you recover the audio signal.