frequency detector

[mackrackit]

thanks Mac are you thinking that, that is my problem?

Yes, The signal would need to be around 4 volts for the pic to detect it.
Alan has a good solution too.

[grounded]

think to you both.
I'm a little green this stuff and have never used the comparators part of these
little big boy toys. (and gals) so I will start learning what I can. if there is anything that yo care to share on the matter I'm all ears.
I'm just a hobbyist and enjoy learning from this forum and I'm trying hard not to be a pain in the butt.

[timmers]

Hi,

The PIC lives in a digital world where evrything is between 0v and 5v. Video lies in the analogue world, a strange and wonderful world it is too... But everything in analogue video does not live within the 0v to 5v parameter.

Video feeds are often AC coupled through a capacitor and require an amplifier and a DC clamp circuit before they can be sampled. Easiest way to interface to video is to use a dedicated sync seperator which can perform all the analogue processing and output into the digital domain. Take a look at National LM1881 for example.

PAL video sync is 300mV with the video sitting a further 700mV above that. Total amplitude is 1v peak to peak. The sync is a composite sync containing short pulses for line sync, longer pulses for frame sync and equalising pulses between the two. There is a good description of video sync structure in the LM1881 data sheet.

Tim.

[grounded]

thanks
so it data sheet, Google and print PDF time.
like I said using the NE567 work fine just thinking it would be easy todoall with 12f629 but look a lot more than I thought
any search tips?
thanks as always

[fronkensteen]

thanks
so it data sheet, Google and print PDF time.
like I said using the NE567 work fine just thinking it would be easy todoall with 12f629 but look a lot more than I thought
any search tips?
thanks as always

You want just the 15.75Khz signal and you're trying to count just that 15.75Khz signal to detect the presence of a video signal.
One of the problems is the fact that there's a lot more going on than just that 15.75Khz signal, so you're probably counting a heck of a lot more than just that.

Maybe add a fairly tight bandpass filter in front of your input/amplifier and see what happens.
Mostly though I think I would put an o-scope on the input pin and see what you actually looking at.