Using AVRcam hardware with ov7620

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Using AVRcam hardware with ov7620

Postby tlclotus » Sat Dec 04, 2004 12:27 pm

Thank you very much for open source releasing the details of AVRcam.

I am studying the documentation to determine if the hardwave will support my existing ov7620 prior to purchasing the hardware.

It is truly a joy to read properly written and documentated source code.
tlclotus
 
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Joined: Sat Dec 04, 2004 12:14 pm
Location: Newtown Connecticut

Postby Guest » Sun Dec 05, 2004 4:39 pm

Hello,
When I first started working on the AVRcam about nine months ago, I was planning on using the OV7620 since I really wanted to be able to view the NTSC output from that camera. I was planning on having to play some subsampling games with the data, since VGA was far more data than I wanted to have to process with the AVRcam. At this point, I hadn't stumbled on to the idea of clocking the AVR and the camera with the same clock source to provide the synchrnonization that I needed. As soon as I realized that this was the way to go, the 27 MHz crystal that is part of the common OV7620-based camera board was going to be too fast for the AVR to keep up. So I gave up on the NTSC output and switched to the OV6620, which uses the 17.7 MHz clock that could be used to clock the AVR directly, and thus provide this synchronization that is needed to make the system work.

The other potential way to make it all work is to run the OV7620 clock output (the 27 MHz signal) into a divide-by-two circuit (could be as simple as a flip-flop), and then clock the AVR with the resultant 13.5 MHz signal. This is obviously in the range of usability for the AVR, and you'd have to be subsampling the data anyway (again, VGA data is just too much for the AVR to do the tracking). It would require more investigation to see what kind of signals would potentially be missed if your AVR was executing an instruction at half the rate the camera was being clocked (i.e., if the camera produced a signal that was asserted for only one single period of the 1/27 MHz clock, it could be missed).

My wife is bugging me to go to the grocery store....I'll think more about it and post back if I come up with any other ways to make it work...
Guest
 


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