I am developing a little circuit to control a servo linear actuator that is used to control fine injection onto a microscopy set-up. I am using a 555 circuit (see below) to generate the PPM signal required to control the actuator position with a couple of slide pots.
It contains three pots, a "coarse" slide pot to control the servo position, a "fine" slide pot (with audio taper) and a pot that sets the range of the "Fine" pot. The user will preset the coarse and range pots and then, at a particular time-point, gradually slide the fine pot over its full range until it reaches zero resistance. When it reaches zero resistance I would like an LED, positioned close to the microscope, to give a brief flash (~35ms). This way we can align the moment of injection with the video recording of our microscope slide. Does anyone have an idea how to add that to this circuit?