[cpia] Can I use multiple cameras???

[sbertin@mindspring.com]

On  7 Apr, Carlos Ernesto López Natarén wrote:
> I want to make a kindergarden monitor for five classrooms using
> 5 Web cams II, my main concern is in how to connect them in the
> server

You'll need 1 parallel port for each camera.  The kernel can support up
to 8 parallel ports.

> assuming I can connect them all in
> the computer, just inserting the cpia and cpia_pp (cpia_usb) modules
> the cameras will be detected??? I mean how many cameras can be
> detected???

The cpia_pp driver supports as many cameras as the kernel supports
parallel ports.  Video4Linux supports up to 64 video capture devices, so
that would probably be the limit for USB.

Those are code limits, there are practical limits also.  With more that
2 or 3 parallel port cameras, you will run out of DMAs.  That means that
additional cameras will need MUCH more CPU time to read from the port,
and a faster CPU may not help much. At that point USB is probably a
better option.

USB also has its limits. Each camera needs at least 2.5Mb/s. With 12Mb/s
available bandwidth, that means a max of 4 cameras active at once.  To
get that low bandwidth usage would probably require hardware and driver
modifications.  The current driver with most cameras will need 7.4Mb/s,
so only 1 active at a time.

> the next problem is assuming I can put them all in the "hub" how can
> I amplify the signal from the cameras because the five rooms are
> separated and I need some extra cable to concentrate all the cameras
> ports.

I have seen devices to extend the cable length for printers, but I doubt
they would work with cameras.

Scott J. Bertin
sbertin@mindspring.com