Hot-shoe signal to external GPS

ProfHankD wrote:

DPR_gio wrote:

I have a Nikon D3300, and I have connected, thorough a specific accessory (http://www.seagulluav.com/product/seagull-sync/?v=cd32106bcb6d), the hot-shoe 'signal' to the 'external-event' time-mark pin of an Ublox M8T GPS receiver: this way, every time I shoot a picture the shutter activation, through the above hot-shoe circuit, sends a signal to the GPS which then records the precise time when the image was taken.

The hot shoe adapter is supplied by (a 3.7 V Li-Po battery connected to) a 3.3 V regulator, and hardware-wise things seem to work: the issue I'm facing though is that not all the 'shutter activation pulses' are detected and logged consistently by the GPS unit, and I suspect this depends on the hot-shoe signal duration (being too short at times...?? not sure) - the GPS time mark pin operates at TTL level, can detect falling or rising edge pulses, and it's fairly flexible and reliable.

The hot shoe on most modern cameras is an electronic switch that can handle at least 5V and usually 24V; older cameras used mechanical switches and could tolerate much higher voltages (and significant currents). I believe it switches between connected and not connected, not logic low (ground) and logic high (3.7V? 5V?). If so, the problem is that switching between logic high and floating will not give a clean edge However, I don't have a copy of ISO 518:2006... you should really trust whatever that says we are supposed to use, not my memory....

ISO 518:2006 only specifies the physical dimensions of camera accessory shoes. The electrical specifications are in ISO 10330. For electronic switches, it states that whatever voltage (max 24 V) that is asserted on the center pin by a flash, should be pulled down to 1.5 V or lower in one µs or less and be kept there for at least ten µs.