[Metalab] Cheap (Web)cams?

[Herbert Poetzl]

On Sun, Mar 03, 2019 at 06:11:38PM +0100, leopold zyka wrote:
> Hi,

Hey Leopold,

> I have some usecases where I would need a lot of cheap webcams.

What resolution and what framerate are we talking about?

> One application is 3D scanning. 
> The project 3DScan uses 100 Raspberry Pi cams:
> http://www.pi3dscan.com/
> Here you find the costs of the hardware:
> http://www.pi3dscan.com/index.php/cost

> So I am thinking how we could make this cheaper.

Really depends on the number of cameras as well as the
resultion, framerate and total bandwidth you have in
mind.

> *MIP CSI2*
> The raspberry PI cams and all the cams used in mobile phones
> don’t use an USB interface. They use CSI-2 (*Camera* Serial
> Interface Type 2) with a 15 pin ZIF 15 socket.

> A widely adopted, simple, high-speed protocol primarily
> intended for point-to-point image and video transmission
> between cameras and host devices

> https://www.mipi.org/specifications/csi-2

Yeah, unfortunately it is also proprietary and somewhat
problematic to handle, but definitely doable.

> *USB Webcams?*
> An alternative to the would be to use USB-Webcams and don’t
> have 100 hundred decentralized CPUs (Raspberries). 

> The challenge is you need a multi-port USB interface like 
> this:
> https://plugable.com/products/usb3c-hub97xxx/

> One problem with this approach is that there are no 
> multi-port solutions available.

You can actually stack USB hubs to quite some depth
(7 hubs deep device tree) and quite a number of devices
per USB port (127 or 255) so you can use a tree of
powered (this is important) USB hubs or some of the
more expensive 16/28/54 port hubs.

https://www.amazon.com/Adapter-Charging-Individual-Switches-Windows/dp/B07FSJ33X6
https://www.amazon.com/Manhattan-Port-USB-Hub-161718/dp/B0074024XU

Note that you are still limited to the total of 5 Gbps
for each USB 3.0 port, so your bandwidth for 16 devices
will be below USB 2.0 (~300 Mbps) and even less for more

> Due to high demand the above product is unfortunately sold out
> indefinitely.

> I assume that there would be also a bandwidth-problem on the PC
> side.

Yep, see above, you can probably get about 40 USB 2.0
devices at full speed on four USB 3.0 ports.

> *Use Raspberry PI Zero?*
> Using a Raspberry PI Zero would save some money:
> *https://www.pi3dscan.com/index.php/blog2/45-raspberry-pi-zero-v2
> <https://www.pi3dscan.com/index.php/blog2/45-raspberry-pi-zero-v2>*

> https://electronics.semaf.at/Raspberry-Pi-Zero-W-Camera-Kit

> *Use an ESP32-PICO? *https://www.youtube.com/watch?v=B8Jq0G17WgQ

> Maybe it would not work with a cam which has more than 2 MPixels
> resolution.

This would mainly be limited by the Wifi/BT interface
which will not allow you to run more than a few of
those at the same place.


> *Summary*
> For me the best would be to have a module where the cam-module
> already sits on the PCB. 

> This would save connectors, cables (15pin!) and adaptors.
> Also I would prefer to have a waterproof case for outdoor usage.

> *Any Ideas???*

Let's first specify the resolution, frame rate and
total bandwidth required for your applications, then
we can talk interfaces and sensor/camera solutions.

Best,
Herbert

> _______________________________________________
> Metalab mailing list
> Metalab at lists.metalab.at
> https://lists.metalab.at/mailman/listinfo/metalab