| 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 Drawing to view PDF |
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