Thanks to the S6986, the circuit is very simple and requires few components. D2, D3, D5 and D6 forms a bridge rectifier allowing to plug the sensor connector brick in any direction. C1 filters power supply, it must be connected near to IC1 to bypass it properly. IC1 is the Hamamatsu S6986 sensor, the `heart` of this sensor. LED output drives the laser with a 1/16 duty cycle, and the included photodiode collects reflected light. Internal processing circuitry correlates the received light to the emitted light, this enables very reliable detection even with high ambient light.
When S6986 receives enough reflected light, its output goes to the low level (R1 limits the current), and the RCX sensor input becomes "true". Note that this sensor only returns a boolean value, "true" if the target is in laser beam, &