Previous Posts:
TI and Würth Elektronik LED RoadTest+ application and un-boxing - Blog 1 - Nov 10
LED Road Test - Software issues - Blog 2 - Nov 26
LED Road Test - LED PCB issues - Blog 3 - Dec 5
Related links:
search for a PCB for Würth power leds
Introduction
Today I like to explain timing issues related to my project. As explained in my first blog the concept of the controller is to operate in pulsed mode in which the lighting is switched on only when required. The controller receives a trigger signal when a pulse is required. The delay from the trigger to the output pulse, the length of the pulse and the intensity of the pulse all needs to be configurable.
Timing diagrams
Lets go into more detail. After an internal or external trigger pulse, the LEDs needs to be switched on for a certain duration, and switched off afterwards.
But commonly the camera electronics are not immediately ready after a trigger pulse, so it can be that the image capture starts to late, resulting in less light, or even no light at all when it takes longer than the duration value (remember we are talking about pulses of micro seconds). Therefore a configurable delay time is needed.
The trigger pulse can be generated internal in the flash controller, or come from outside the controller, generated by the camera or an external event. In case it doesn't come from the camera, that also needs to be triggered. Therefore the flash controller will also have a trigger output to the camera. This trigger also needs a configurable duration and delay time.
By using these four parameters (flash duration and delay, camera duration and delay) we have a very flexible solution.
Lets also draw the external trigger.
This gives us our fifth parameter, the selection between an external or internal trigger.
Finally, after the first internal trigger pulse we like to give a second one and a third one etc. So we also need to set the internal trigger pulse interval.
Below is the complete picture, with all six configurable parameters marked yellow. (internal/external trigger is counted as one parameter).
Next post I will start implementing this in a software user interface.
stay tuned.
