4 Wire vs 5 Wire TTL Strobe

My old Sea and Sea YS50 strobe has a 4 wire cable. My newer Sea and Sea YS110 strobes use a 5 wire cable. I needed to understand the difference so that I could adjust my quench controller to operate the YS110.

Cameras Underwater has a great write up about the cable pinouts and operation of several strobe interfaces. I had focused on the minimal 3 signal wires (Ground, X & Q) as I was not interested in any of the "extra" features that may be available. So I went back to this to see what I had missed.

The extra wire in the 4 pin YS50 Sea and Sea Motormarine II interface was the S (integration) signal that was used to control the exposure circuitry in the Motormarine camera. I definitely did not need this. 3 wires was enough for the YS50.

The extra wires in the 5 pin Nikonos interface were SP and RDY. There was some confusion since the 5 pin Sea and Sea Duo flash interface was documented as well. And it uses the same strobe connector as the YS110. The extra pins in the 5 pin Sea and Sea Duo interface were SP and RDY/S. Where the Nikonos and Duo interfaces different? Which one did my YS110 use?

Some quick google research regarding the Sea and Sea Duo interface provided an answer. Sea and Sea marketed a series of strobes that talked both the Motormarine II protocol AND the Nikonos protocol. The YS120 Duo  is one example. I could safely ignore the Duo interface and concentrate on the Nikonos interface.

The SP signal is used by the strobe to indicate to the camera that the strobe is capable of TTL operation. Handy but not of any use to me since I already know that my strobes can support wired TTL.

The RDY signal line is used by the strobe to indicate that it is ready. Doh!

The X signal line on the YS50 is dual purpose: it indicates the strobe is ready and it is used by the camera to fire strobe. The good folk at Nikon separated these and provided a dedicated wire for each function in the Nikonos interface. Problem identified. The solution proved trivial as I had used a separate Arduino analog input to monitor the strobe ready condition. A small modification to my test rig wiring harness for the YS110 and the standalone RDY signal could be routed to the analog input I was using to detect the strobe ready.

I could now reliably detect when a single YS110 strobe was ready to fire.

Subsequent inspection of the Sea & Sea TTL converter revealed that life may not be as simple as I thought. The stock converter only used 3 wires (Ground, X & Q). It ignored the strobe RDY signal. Seems like some additional investigation may be required?