To use the OPB885CZ sensor with an opaque target, adjust the phototransistor load resistance to 2.5 Kohm by placing the shorting bar on the board between pins 1 and 2 of the header. Insure that no object is blocking the sensor gap, and then initiate the calibrating process by momentarily grounding pin 4 of connector J1. After approximately 2-3 seconds a green LED should flash three times to indicate a successful calibration. There should now be no LEDs lit if the board calibrated successfully. If instead the red LED is on, change the load resistor to a larger value and repeat the calibration process.