Lomax
Posts: 189
Joined: Wed May 20, 2015 9:43 pm

CSI FPC DIP15 to round cable

Thu Feb 09, 2017 6:39 am

I'm trying to design and build an as small as possible enclosure for a RasPi camera board, and I was planning to use these HDMI adapter boards to extend the cable. But having modeled the layout it's clear that significant space saving could be achieved if rather than going to an HDMI socket the FPC went to solder pads, for soldering the extension cable to. HDMI connectors are pretty fat (~7-8mm), and I would have to allow space for the male connector housing as well - in all it adds over a centimetre to the depth of my enclosure, or about 1/4 of the total depth. I've never snipped an HDMI cable, and can imagine the wires are quite thin, but maybe a 6-pair (individually shielded) cable such as this one? The maximum cable length we're talking about is three or four meters. I've looked at the pinout for the CSI port - it ought to be possible to use just 12 conductors, and perhaps even fewer? Another reason why a soldered cable is preferable is that the camera is going to be outside; it's easier to make the cable entry watertight, and a soldered connection won't degrade due to moisture. What do you guys think? Does anyone know where I might find a FPC DIP15 breakout board with solder pads?

RareHare
Posts: 89
Joined: Thu Jun 20, 2013 7:17 pm

Re: CSI FPC DIP15 to round cable

Sat Feb 11, 2017 8:45 pm

You are right in that you only need 12 conductors. You could get away with not connecting CAM_CLK, as it is used to control the red LED on the v1.3 camera module, but the other 11 are necessary. Therefore, I would just do all 12.

Indeed, all the GND wires are electrically connected. If you want to go with a super-flat cable concoction, it is OK to remove the wires from their jacket and solder them directly to a (very short if desired) 15-pin FFC cable. Then, the 6 pairs could be laid flat, and enter directly into your enclosure. That is probably as flat as you can get it. Naturally, on the other end of the pairs, you'd have another solder to 15-pin FFC.

The pairs that you want to be careful with are the two data pairs and the clock pair. You want to endeavor to keep these three pairs the same length to minimize clock skew, where the clock signal, now coming from the camera module (whereas before, it came from the RPi), establishes when the RPi should start sampling chunks of data from the data lanes. Especially if you are using electrodynamically-advantageous twisted pair, you also want to do something to keep two wires of a critical pair from separating (I know...I know...That's what the JACKET is for!...one says...), because the lobes of the twists are important, in that they assist in noise self-cancellation.

The CAM_GPIO, CAM_CLK, SDA, SCL, Vcc, and GND require less care. This is obvious for Vcc, GND, CAM_GPIO, and CAM_CLK (remember, LED, not a clock). For SDA and SCL, the maximum 1st harmonic of signal is 400kHz, IIRC, so you can be abusive somewhat with their conductors.

Lomax
Posts: 189
Joined: Wed May 20, 2015 9:43 pm

Re: CSI FPC DIP15 to round cable

Tue Feb 14, 2017 6:16 am

RareHare wrote:You are right in that you only need 12 conductors. You could get away with not connecting CAM_CLK, as it is used to control the red LED on the v1.3 camera module, but the other 11 are necessary. Therefore, I would just do all 12. Indeed, all the GND wires are electrically connected.
Thanks, that's great to hear. I really do need the LED line though, since it controls the IR filter on my camera. I also need a 13th line to control the tilt servo I'm using, and a 14th one for +5V. I see the HDMI connectors have 19 pins, which is how there can be an additional 4 control pins on the adapter boards. It sounds like an individually shielded 8-pair cable is the way to go, with ~0.2mm2 conductors. Won't be cheap though!
RareHare wrote:If you want to go with a super-flat cable concoction, it is OK to remove the wires from their jacket and solder them directly to a (very short if desired) 15-pin FFC cable.
Can you solder directly onto FFC cables then? I thought they would melt as soon as you look at them with a soldering iron in hand. Another option would be to get hold of some DIP15 FPC connectors, and knock out my own adapter boards - would be nice to have something you can screw down.
RareHare wrote:The pairs that you want to be careful with are the two data pairs and the clock pair.
Noted.
RareHare wrote:For SDA and SCL, the maximum 1st harmonic of signal is 400kHz, IIRC, so you can be abusive somewhat with their conductors.
Good to know, I worried I2C wouldn't work at all! Should I run these as a pair though, or are they best kept separate?

Lomax
Posts: 189
Joined: Wed May 20, 2015 9:43 pm

Re: CSI FPC DIP15 to round cable

Tue Feb 14, 2017 12:32 pm

I found some cheap 1mm pitch FFC 15-pin connectors on eBay, so will give the PCB route a go.

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