cmos camera with a pic

On 24 Jul, in article
     <1153788222.114025.278700@b28g2000cwb.googlegroups.com>
     beto.barba@gmail.com "peres" wrote:

>which microcontroller will be good for the job?, just need to store a
>320*240 8-bit grayscale still image ... thats 76,800 bytes. which
>controller do you recommend?

How the problem is approached depends on MANY factors

        1/ pixel resolution and depth (bits per pixel)
        2/ Is the object moving or not (not = rock solid still)
        3/ how many images are to be captured (update rate)
        4/ How fast does the individual images have to be captured
           bearing in mind lighting levels, exposure time, lenses
           and object characteristics.
        5/ How the image is transferred and to what device or comms link
           is another issue determining system configuration and hence
           controller.

>im seeing the rabbits which had lots of RAM but i dont have any
>experience in them... what do you recommend for the job?

Most 8/16 bit controllers do not have a bus or ports fast enough to
capture continuous data at 5MB/s and greater so the choices are

        a) use external frame grabber/field memory to grab whole frame
           into fast memory and readout slowly. Can be done with CPLD
           and SRAM chip.

        b) Use some form of successive capture using fifos for n lines
           at a time, often needs CPLD or similar to accurately time
           acquisition of line starts to fifo.

        c) Use some form of successive capture to grab specific pixels
           in multiple lines which requires accurrate timing to grab the
           pixels on each frame from different portions of a line.

The controller really must have the ability to address memory either as a
large window of the memory of the external stored frame or the whole frame.

Considering the delays and complexities of dealing with windowed frame stores
or successive frame capture it is generally easier and overall cheaper in time
and money to use an external whole frame store.

It is usually easier to use a controller that has an address bus larger than
16 bits and be able to access the memory via a CPLD from the controller or
by the CPLD writing to the memory when acquiring the image. It does not
require a large device to do this. The amount of special registers that have
to be created to control the grabber/dual port frame store is miniscule and
adding an interupt o/p to signify end of frame capture is useful.

By using bidirectional buffer chips (e.g. 74xx245) between the SRAM and the
controller and the camera interface only a few enable signals are required
from the CPLD to control data flow if size of CPLD is an issue.

The controller really needs to have 4KB or more of internal RAM for your
system and buffering or conversions of data prior to transmission

The main thing is keep the Video data memory as external to the controller
chip for most small controllers. If you have some fancy large chip with
a camera controller ensure its bus can transfer the data and will not
cause other issues like watchdog or similar problems. The other issue
with larger controllers is which memory is being written to (internal/external)
and does it require to go through special memory controllers (e.g.SDRAM)
and what effects that will have.

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.gnuh8.org.uk/>              GNU H8 & mailing list info
<http://www.badweb.org.uk/>             For those web sites you hate

"peres" <beto.barba@gmail.com> wrote in message
news:1153590062.042147.200630@h48g2000cwc.googlegroups.com...
> Hi, i need only to store a picture when an event happens, i want to do
> it with a pic16f876A, i dont need to do any kind of image processing i
> think, just take a picture and store it into a flash, so my question is
> what cmos camera do you recomend for this?
>
> thank you in advance
>

Erm, think dsPIC and dumping the image straight into SRAM.  Aside from that,
a 16f pic can do 20Mhz tops which is 4,000,000 single cycle instructions per
second.  Definitely would need a dsPIC to handle this, and then you have to
put the data somewhere.  Some of the top end pics 'could' store this
internally as they have enough RAM, and also you can write to the program
ROM, although the problem there is EEPROMing into that ROM.

dsPIC and SRAM.  Might just be possible with one of the 18f's overclocked at
60Mhz, that'd give u....  60,000,000 / 4 = 15,000,000 single cycles
instructions per second.  For a 5MIPS stream as has been already mentioned
that only gives you 3 cycles per chunk of data coming from the camera.

yep, dsPIC and SRAM, using the dsPIC to simply oversee the control lines of
the SRAM as the data is being dumped into it.  Then you're in a position to
chug that data out over a 9,600 RS232 line if you really wanted.  16f's will
barely keep up with anything data intensive, a 16f628a can barely manage a
PS2 mouse.

peres wrote:
> Hi, i need only to store a picture when an event happens, i want to do
> it with a pic16f876A, i dont need to do any kind of image processing i
> think, just take a picture and store it into a flash, so my question is
> what cmos camera do you recomend for this?

A number of years ago I used a black and white (well, 8 bit grayscale
actually) module with a PIC. The module (sorry, can't find a link) had
8 data bits out and a pixel clock which I was able to use to clock a
binary address counter. The address counter was interfaced with a
static RAM so the data was copied into the RAM in real time. The PIC
then read the data out of the RAM at it's much slower speed and
compressed and sent the data over a serial port at up to 56Kbaud. I
would think that with the 18 series PIC's you could do better.

have you looked at the CMU cam?
http://www.cs.cmu.edu/~cmucam/home.html
there is another one like this out there but I cant remember what its
called.
-howy

peres wrote:
> Hi, i need only to store a picture when an event happens, i want to do
> it with a pic16f876A, i dont need to do any kind of image processing i