I'm working on a project, a ballistics chronograph. Basically a light sensor which will send a certain voltage to the Arduino until it is tripped by a bullet. Then the voltage will change very briefly while the bullet is between the light sensor and the light source. The ADC is far too slow, so I am trying to use the digital pins.
Using direct bit reads, I can sample the pin plenty fast enough to detect the bullet. However, due to the pin hysteresis, the ATMEGA's digital pins can't actually read the small change in voltage very well. Is there some way to eliminate the input hysteresis so that it always trips at a certain voltage? Or do I have to move to a different controller (like a Teensy)?