Re: [Gumstix-users] Long camera cable

[Simon K. <sim...@pg...>]

Hi itodroid and Jason,

On 14/01/2012, at 4:06 AM, itodroid wrote:

> Simon,
> 
> Depending on your definition of "some distance", you may have a challenge on
> your hands.  We switched from the 3" cable to a 6" cable and immediately
> found that there were EMI/noise issues.  While shielding does help, I'm not
> sure if it scales to your distance.  (Thank you, Reynolds Wrap Heavy Duty
> Aluminum foil)

We're looking at around 6"–12" (unsure of the exact length yet). Hmm, this doesn't look hopeful. 

> FYI, we used Gumstix's recommendation of contacting Flexconn
> (www.flexconn.com.tw).  They also have a shielded version of the FFC cable
> that we are looking into using as well.

Thanks for that link, I hadn't seen that recommendation. Their finest pitch seems to be 0.5 mm though?


On 14/01/2012, at 7:27 AM, Jason C. Mecham wrote:

> On one project I used the FIN212ACMLX SerDer (available from Digikey for around $3.0EA)
> 
> It's only major limitation is that its only capable of 40MHz. So that limits the pixel clock to that.

Yes, that approach had crossed my mind. I think I'll try to find a long cable first and if it's too susceptible to EMI I'll try this. 

> Note - I did design a prototype (for the beagleboard-XM) using that chip, but I found that the OMAP ISP was too sensitive to EMI/ESD events to be really usable with that solution. Any interruption of the vsync/hsync lines causes the video (in preview mode) to lose sync. It doesn't always just resync up to the next vertical sync like you'd expect it to. I'm not ruling out that I could have made a mistake in design/layout that made the FIN212 not work as well as just a parallel shielded interface. It will work for days, and then one cold dry day you touch some nearby large metal object and then suddenly the video is shifted by a few vertical lines, and the debayer is off. 

Useful info, thanks.

> Regardless of what camera interface you use I would highly recommend testing it with an ESD gun (to simulate a nearby esd event using +/-8KV) as early in the design cycle as you can if this will be used in an actual product. In my experience with it any small length was okay (a few inches), and anything around 18inches was just more sensitive than I wanted.
> 
> 
> I'm really hoping someone can come out with gumstix/beagleboard/omap3 camera that's meant to work at 6ft, and not only generates low EMI but is also very immune to nearby EMI events. 

That would be great, but I don't think it's going to be me! 


Thank you both for your advice.

Regards,
Simon.