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Freespace Communication Circuits, Page 4
(Light Beam Communication Circuits)
Circuits designed by David Johnson, P.E. Last Updated on:
Thursday, December 01, 2011 07:15 AM The contents & graphics
of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB
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MICRO POWER 40KHz BURST LASER DIODE DRIVER
Some laser tag or simulated combat games can use this circuit to send short bursts
of modulated laser light at the opponent's vest, equipped with a matching light
receiver. The circuit operates from three 1.5v cells (4.5v) that should provide
enough energy for about 200,000 shots.
OPTICAL RFID TEST CIRCUIT
I designed this test the concept of using light techniques to send identification
data instead of RF. A more detailed discussion on this scheme can be found in the
Imagineered new products section.
PULSED LED TEST CIRCUIT
This circuit is designed to test visible and infrared LEDs in pulsed mode
operations. It can drive the LED with peak currents in excess of 10 amps. A light
detector nearby can monitor the response time and intensity of the LED under test.
SIMPLE NITROGEN SPARK GENERATOR
Nitrogen or air sparks are very powerful light sources that produce flashes that
last only a few nanoseconds. This line powered circuit generates a continuous series
of very small sparks across electrodes with a 0.05 inch gap.
SINGLE IC FORMS SENSITIVE MODULATED LIGHT RECEIVER
The circuit uses a very inexpensive C-MOS IC that is connected to a small
photodiode. Using an unique inductive feedback network, the circuit provides high
sensitivity under high ambient light conditions. It is a great circuit when you want
to extend the range of an optical remote control transmitter.
VOLTAGE TO FREQUENCY CONVERTER + 1uS LED PULSE DRIVER
This circuit receives the signal from the above amplifier and launches powerful 1uS
infrared light pulses from a low cost LED that are frequency modulated by the audio
information. The 10KHz center frequency of the pulse stream is low enough so a
standard infrared LED can emit ten times more light than conventional long pulse
techniques. The circuit is described in more detail in the transmitter section of
Dave Johnson's
Handbook of Optical Through the Air Communications. (this link is off-site)
WIDE BAND ZERO CROSS DETECTOR
This circuit was designed to convert a low amplitude 40KHz signal into a clean
square wave signal. It will work with inputs as small as 5mv peak to peak or
as large as 3 volts peak to peak. The input frequency can range from a few
kilohertz to about 150KHz.
XENON LAMP FLASH DETECTOR
This circuit uses a small 2.5mm square photo diode in conjunction with a 100mH coil
to detect the short light flashes from a xenon lamp. The coil makes the
circuit immune to normal room lights. Its 10mv sensitivity can detect light
flashes from a range of over 100 feet. Reflections from a room’s walls and
ceiling is usually enough to trigger the circuit. The entire circuit draws
only 3 microamps from a 6 to 9 volt battery.
