Here is a suggested starting point for the optical sensor circuit. When light is blocked to the sensor the collector resistor raises the output HI. The sensor outputs are each fed to a Schmitt trigger to give a clean transition. The Upper Sensor transition is high-pass filtered to give ~10 μsec negative pulse to trigger the monostable which generates the speed limit pulse (pulse width is set by varying the resistor in the 555 RC time constant - not shown). If the Lower Sensor signal appears before the limit pulse terminates, then a trigger pulse is generated during the overlap interval. Note that no monostable pulse can be generated unless the lift pipe is first raised high enough to activate the Upper Sensor.
![EP-69.png EP-69.png](https://maker.pro/forums/data/attachments/19/19677-642cd541bfb1840ce4b2edb0cbe30ef5.jpg)
![EP-69.png EP-69.png](https://maker.pro/forums/data/attachments/19/19677-642cd541bfb1840ce4b2edb0cbe30ef5.jpg)