I want to read rpm of an engine flywheel. I thought of either doing this with a hall effect sensor and magnet on the flywheel, or somthing else I have seen done is the flywheel painted black with a white line. There is a IR led directed at the flywheel and a IR sensor, when the white line passed the sensor it reflects the IR light to the sensor.
But I do not know which type of sensor to use. I have sensors used for IR remotes, and I also have another setup from a robot for "line detection".
The one from the robot is from a cybot. http://en.wikipedia.org/wiki/Real_Robots
From what I can tell it has an IR led, and another 2 pin device that looks like an led. My guess is, that its resistance changes with the amount of IR detected.
What is the best way to measure the rpm of the flywheel?