Redwood Shores, 14 mei 2007.

Sparkfun electronics (http://www.sparkfun.com) has several CMOS cameras, and
even had a challenge on interfacing with one. I read the results, and it
actually is relatively simple to interface: generally you apply a clock
signal, and on the databus you get each pixel's value, and signals that
indicate it goes to the next line or the next frame. Sometimes there is a
separate I2C interface (usually at 3.3V) which allows you to select how the
pixel data is formatted. Most cameras aren't at all critical about the speed
of the clock. So far the easy part. The hard parts are the following:

1) Even the most simple CMOS camera generates an image of 640*480. That is
307200 bytes of data, if you want grayscale output, and double that at
16-bit colour. Even if you take only a quarter of that (some cameras allow
you to reduce the resolution using the I2C interface, but you could just
take every other sample and skip lines) that is still more than your PIC
will ever be able to store.

2) The fact that the camera isn't critical of the clock speed doesn't mean
you shouldn't be. The slower you read the clock, the more the image can
change while you are reading. If you want to capture a completely static
image, that is fine, but if there is anything moving on the visual (and
usually moving things, like cats and people, are the more interesting things
for a camera) you really want to capture a full frame within 1/25th of a
second. That implies a consistent data rate of at least 4 MB/s, which is
generally not something PICs are known for.

All solutions I've seen use a simple FPGA and external memory chip to buffer
the image, and then allow the PIC to read the memory at leisure.

Greetings,
Maarten Hofman.



2007/5/14, Dario Greggio <adpm.to@inwind.it>:
>
> Lind, Allan wrote:
>
> > Anyone had experience interfacing a PIC with a low cost CMOS camera such
> > as found in cell phones?
>
> there was a thread on the Forum some time ago:
> http://forum.microchip.com/tm.aspx?m=236199&mpage=3&key=
>
> take a look at it
>
> --
> Ciao, Dario
> --
> ADPM Synthesis sas - Torino
> --
> http://www.adpm.tk
>
>
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