Canon EOS hot shoe pinout

[ylazimy]

Has anyone figured out the functionality of the four small pins on the Canon EOS hotshoe? I'd like to at least know their direction and voltage levels, so I can build a repeater system for long-range wired flash operation using the full ETTL-II feature set. Of course, the easy way to do this is to bypass the hotshoe altogether and wire directly to the LED driver (which transmits all the relevant information for wireless operation), but this would require hacking into an expensive flash unit, which then needs to be bought instead of rented or borrowed.

Here are my thoughts on the matter from a purely inductive analysis - please check my logic here:

At least one of the pins must be a serial comm port from the camera to the flash, and another must be a serial comm from flash to camera. The other two must then either be: a) the inverse phases of these signals in a balanced transmission system; b) some sort of 2-bit designation code for either flash or camera; c) additional serial lines; d) handshaking or clock lines for the first two comm ports; e) directly connected to the first two comm ports; or f) reserved for future use. Option (a) is unlikely since Canon states the maximum recommended transmission length is only 10 meters. Option (b) would only allow for 4 different codes, and I doubt they would have limited themselves so severely - heck, there's already four different flash protocols out there (TTL, A-TTL, E-TTL, and E-TTL II). Option (e) makes sense if they had to run a lot of current and wanted to save space by using two pins instead of one big one, but if they were running that hot, they wouldn't have the 10m range limitation. This leaves options (c), (d) or (f). The strange thing is that no voltage shows up between the hotshoe rim on my 20D and any of the pins, which tells me that these are all powered by the flash. If this is correct, then all the signals are from the camera to the flash. However, I believe there are some E-TTL features that indicate the flash is communicating with the camera.


I should eventually figure this all out myself once I get access to some cabling I can psit off and place on an o-scope. I'll make sure and post my findings incase any of you other hackers are interested in this sort of thing.

[nkg]

I've never seen anyone who has posted the reverse-engineered specs for the flash protocol. I'd love to hear from you if you do!

[skowerr]

do you know any way of making ttl macro flash (canon macro ring lite ml-3) work witk a rebel xt camera???

[nkg]

[Guest]

thanks for fast reply
maybe you know the pinout of canon hot shoe and ttl and e-ttl signals???

[nkg]