[Kinda SOLVED] Custom camera module for CM3+: cables and crypto chip

[zontar]

I am building my first project with CM3+ , and designing a custom PCB carrier board. I've prototyped the final board with various breakout boards and smaller PCB and the overall project works.
Now I need to complete it: the project requires an external camera, placed a few feet away from the CM board, let's say 4 to 5 feet.

In an earlier prototype I've managed to use a raspberry Pi Zero + HDMI adapter from Petit Studio . It works with a pair of smallish(1"x1") PCBs with a FPC connector on one end and a HDMI female connector on the other, and by using the data pairs in the HDMI spec to pass the data pairs in the camera, it actually works. I've tested with 10 feet HDMI cables and it's ok with 30fps at VGA resolution (which is my use case).

Now I wanted to get rid of the cumbersome HDMI plugs and the above small adapter PCBs and I'd like to design my own camera module with the Sony IMX219 sensor directly attached to either a micro HDMI female socket or mini Displayport socket. On the CM carrier board I'd replicate the socket and by connecting to the correct GPIO pins it should work.

I have two questions:

• is it correct that I can build my own camera module with the Sony IMX219 skipping the ATSHA204A crypto chip, and by replicating the rest of the PCB layout copying the relevant bits from the Camrea v2 schematics?Reading the docs and the forums it seems so, but the sentence says "it is NOT necessary to incorporate the crypto chip used on the Raspberry Pi–designed camera boards when attaching the OM5647 or IMX219 Camera Modules directly to the CM carrier board." and in this case the camera is not technically attached directly to the CM...
• does anybody know of other robust and cheap cables that carry three differential pairs of data signals plus ground N=and at least a handful of other signals? Ideally the cables would have smallish plugs and be readily available. I've searched for mini HDMI <-> mini HDMI but have found none. I've only found mini Displayport over mini Displayport which carry 20 signals and at least 3 pairs of signals and should be equivalent to HDMI for my purposes. Maybe USB-C? But maybe there is the problem that the cable can be inserted either way?

Thanks,
Z

[stuartclark]

Technically you can use any connector you like, but presumably you are hoping to use pre-existing cables rather than making your own?

The general problem with using any of your suggestions is twofold:

1. Those cables all have a specific usage which presumably you wouldn't be respecting - so people may plug in things you aren't expecting (e.g. for USB-C many cables actually contain active electronics, rather than just being bits of wire) possibly breaking things (if someone plugged the camera into the displayport on their laptop would it break either?)

2. All differential pairs are not equal - the different cables are designed for the specific specification which may not agree with what you actually want. For example different specs may expect different impedances or levels of allowed shielding/crosstalk. Equally there may be different versions of a spec which have slightly different characteristics (e.g. different versions of USB and the associated cables).

I would be quite cautious about reusing existing complex cables, especially if this is intended for use by non-technical users - the last thing you want are people breaking the system or other equipment due to mistaking it for a "real" USB or HDMI cable, or problems caused by cables of varying qualities and stated conformance from different retailers.

[zontar]

Hi stuartclark,

yes, i want to use commercially available cables with typical cost under 10$ for 4 ft..

1. you are right. especially for USB-C i am worried that there could be additional electronics involved. But as far as HDMI is concerned I am sure it works, 'cause I've tested it since a couple of years, and besides I will furnish a basic cable inside the finished product, just telling users that it can be replaced by any cable etc..
As for inserting the camera via a cable into a display port on a Laptop, I don't think it will come any harm to the laptop, but maybe it will fry out the PCB camera, this will be at the owner's risk. But nice point, I will keep it in mind to put a big disclaimer

2. i know, and i will test it, of course. I don't see given my knowledge how else I could do.

At the moment my best bet, yet untested, is mini Displayport. It should be sufficiently dumb, and has an asymmetrical socket.
But the real killer cable would ne mini-HDMI to mini-HDMI which I am sure will work, since it's just a repackaging of the tested HDMi, but unfortunately I am not able to find any..

Thanks
Z

[gsh]

I can confirm that on the compute module products no crypto device is required.

[zontar]

Thanks gsh.
I will then design my PCB camera carrier board!

Z

[MarkDaniels]

Hi zontar

I'm not sure if this is what you are looking for, but CPC appear to offer mini HDMI to mini HDMI cables, 1 metre long at this link:

https://cpc.farnell.com/pro-signal/psg9 ... mi%20cable

They may have longer ones. I just searched mini HDMI cable on their web site.

[zontar]

Hi MarkDaniels,
that was exactly what I've been looking for. Thanks for the info and the link!

At the moment I've sent in printing some miniDisplayport components, since mini DP <-> miniDP are more widely available, but should the whole setup fail, I know I have a backup plan!

On their site I've found also a 6feet cable: 6 feet cable by CPC so this could be viable, even though a 4 or 5 foot should be enough.

Thanks for the link!
Z

[zontar]

Just a quick sum up:
I've managed to use a minDP <--> miniDP cable to connect a custom pcb Camera Board (v.1.3 at the moment) to a CM3+ (Compute module 3+) with a breakout board and a symmetrical miniDP socket.

As per the schematics of camera module v1.3, since they are not officially available, I've been inspired by
https://hackaday.io/project/167794-dual-camera-board-for-ov5674

See picture

IMG_7095.jpg (75.55 KiB) Viewed 200 times

Thanks for all the help on this wonderful board
Z