Strobe Quench Controller Operational Theory
I now needed to transform my Sea & Sea TTL converter into an open loop manual power controller for my YS110 strobes. This would provide a single point of power level control so that I did not need to individually adjust the built-in power knob on both of my strobes. Supporting the Canon eTTL protocol was shuffled to the back burner for a while.
The physical TTL converter provided the following features:
- 2 Nikonos bulkhead connections for my strobes
- a user replaceable battery compartment
- a power level control
- 2 "strobe type" selector controls
This converter does not have an optical sensor of any sort, so creating a closed loop system was not easily feasible. I also preferred an open loop system that delivered a consistent amount of light. This would allow predictable results as I altered other physical aspects like strobe position, orientation and distance from the subject.
At first glance the settings required to use an external manual controller seemed counter-intuitive. External manual control is actually fairly simple:
- set the strobes to TTL mode (what??)
- quench the strobes from the controller based upon the controller power knob setting
Setting the strobes to TTL mode seemed wrong. My goal was manual control. Seems like everything should be set to manual?
Nope! Setting the strobes to manual means that you have instructed the strobes to ignore any external control signals (other than fire) and to rely upon the built-in power setting knob of the strobe. In order to centrally control the strobes they must be placed into an operational mode that allows external control. That would be TTL mode. In TTL mode the strobes expect to be controlled by an external source - generally a camera.
In manual mode the strobes only monitor the X line and then deliver power according to their built-in power knob setting. Any external control signal via the Q line is ignored. So the strobes need to be set to TTL mode for external manual control. In TTL mode the strobes will respond to both the X and Q signals and will (mostly) ignore their built-in power knob. My YS110 strobes support a feature where the built-in power knob provides "micro adjustment" of power output when using a fibre optic sync cable in TTL mode. The built-in power knob is totally ignored when using a wired sync cable in TTL mode.
This reduces our manual controller to a few simple concepts:
- monitor the strobe X lines (pass this to the camera X)
- monitor the camera X line
- monitor the controller power level control (more on this later...)
- when the camera asserts X, assert the strobe X
- delay based upon the controller power level and then assert the strobe Quench line
Sounds simple! But not really.
I was fortunate to have some spare ancient YS50 strobes as well as a spare DX-1G camera that I could
punish use in my research. I whipped up a quick Arduino program and hooked it to a YS50 strobe. The initial results were less than awesome. I had some practical learning to do...