The light from the laser can be directed toward the
detector using a plastic fiber optic light pipe, connected to the laser.
The CA3140 circuit forms a laser light power control
circuit, using the PIN photo diode inside the laser assembly. The
photo diode collects a bit of the laser light launched producing a current at the
3.3K resistor, which is proportional to the laser light power. The circuit
maintains a constant bias current through the laser.
The 74HC14 circuit is a combination of an
oscillator and a laser driver. The driver increases and decreases laser
diode current, producing light pulses matching the oscillator signal. This
electronic circuit can be used with visible red laser diodes as well infrared.