Transmissive Optical Slot Sensor

Sensor comprising an infrared emitter and phototransistor on opposite sides of a 3.1mm gap.
Applications include limit position sensor, encoder, counter, optical switch, etc.
Emitter: Ifmax = 60mA, Vf = 1.25V.
Transistor output: Ic=4mA with If=20mA & Vce=5V. Icmax=200mA pulsed <20ms.
Example circuit: