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