Anyone know about PWM?

Thread Starter


Joined Feb 17, 2008

Im about to start a project on it and want to put some background into my introduction which i have to do before doing the practical.

I have hypothesised on most of the experiments im going to do but im unsure what to predict on this...

Using pwm to encode an audio signal into digital form in order to send it down a fibre optic link and decode it using a filter.

You will connect an mp3 into a headphone socket AUDIO IN, set SW1 to AUDIO IN and SW2 to DIRECT etc. Connect your headphones to AUDIO OUT.

(a) Observe the waveform as the music chnages between quieter and louder passages and see the movement of the waveform. What do you think will happen and why is this happening?

(b) Using a fibre optic transmitter and reciever you will send a signal down a 1m cable. A filter will convert the digital signal back to an analouge one..

If you unplug the fibre optic cable from the receiver, the filter input disappeers. The light output should be glowing red. Now vary the dc potentiometer and observe the light output . What do you observe and why? (Can you explian what is providing the filtering action here? Hint- think why movie films dont flicker despite being made up of individual frames.

Real tough, and kinda stupid questions but they got me
Thanks for any ideas.


Joined Jul 17, 2007
Well, this sounds like homework - and if it is, really should've been posted in the homework section.

Is this homework for a school assignment?


Joined Apr 20, 2004
Does to me, too, so I moved it.

Your big problem is in figuring out how to do the audio to PWM conversion. Made any progress on that?

One thing you do not make clear - are you expected to make this stuff in hardware, simulate it, or just do block diagrams on paper?