| I do a lot of
optical electronics work. Often I need to test a modulated light detector hobby
circuit at a particular frequency. The device below has come in handy many times.
I can adjust the frequency of the modulated infrared laser light from about 10KHz to
over 50MHz. 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.
Click on Schematic below to view PDF
version of this Circuit |
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