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Light Beam Communications Circuits
Last Updated on:
Tuesday, April 22, 2008 04:20 PM |
| Circuits Designed by Dave Johnson, P.E. : |
5W FLUORESCENT LAMP INTENSITY MODULATOR
The circuit was designed to experiment with using small fluorescent lamps as a broad pattern source of modulated light. The circuit hits the small lamp with narrow 1us pulses at a rate of 10KHz.
Each pulse launches about 10 watts of visible light. The lamp starting method is a bit crude but the circuit does work.
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9v POWERED XENON PHOTOFLASH Controller
This 9v battery powered circuit is designed for remote control flash needs. A charge control circuit turns off the high voltage generator when the photoflash capacitor is fully charged. A neon
lamp is included to indicate when the system is ready to flash.
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10MHz TO 20MHz LASER LIGHT DETECTOR
This circuit was originally designed to detect laser light pulses for an optical Ethernet communications system. It has good ambient light immunity.
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- 20MHz VCSEL 3mW LASER TEST CIRCUIT
This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that don’t require light output control circuits. The circuit shows how to drive the device from a single
high speed CMOS IC. The circuit can easily be modified to transmit signals from kilohertz to about 50MHz.
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40KHz LASER BURST DETECTOR
This circuit was originally designed to detect weak flashed of laser light bounced off of a fabric video projection screen. It was used as part of a firearm training system. It generates a 100mS
output pulse whenever it detects a 3ms to 5ms laser burst, modulated at 40KHz. It is very sensitive and could be modified for long range laser communications.
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- 40KHZ LED TEST SIGNAL GENERATOR
This 40KHz crystal controlled oscillator circuit drives an infrared LED with powerful 40ma pulses. The circuit can be used to test optical communications circuits, designed to receive
40KHz modulated light signals.
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40KHz Light Detector with Sunlight Immunity NEW
The circuit below was designed to turn on an external 12v relay, whenever it detects light from a nearby LED light source, modulated at 40KHz to 50KHz. This circuit was originally designed
to operate from a fast moving vehicle. The light transmitter was positioned at a stationary position, while the matching receiver was mounted on the vehicle. The circuit has high ambient
light immunity and in most cases, can operate in direct sunlight.
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- 40KHz LIGHT RECEIVER IS IMMUNE TO AMBIENT LIGHT
If you want even more sensitivity than the above circuit, try this design. When used with a one centimeter square photodiode, you can achieve a range of several hundred feet with a standard TV
or VCR remote control module.
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40KHz MODULATED LIGHT DETECTOR
This circuit uses a unique cascode amplifier circuit to convert the current from a PIN photo diode to a current without any feedback network. It is very stable and very sensitive. The
circuit shown has the potential for a conversion factor of 10 volts per microwatt at 900nm. I included a simple JFET post-amplifier with a gain of about 20.
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40KHz TV-VCR LIGHT SOURCE REPEATER
This circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times
more powerful. Using the device, the remote can operate a TV or VCR over three times the normal distance.
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- 1uS LIGHT PULSE DISCRIMINATOR PLUS F TO V CONVERTER
This circuit is designed to detect the narrow 1uS pulses produced by the above amplifier circuit. The clean logic type pulses produced by the discriminator are then sent to a frequency to
voltage converter. The circuit is designed to process a pulse frequency of 10KHz that is frequency modulated by voice audio signals. The circuit is described in more detail in the receiver
circuit section of Dave Johnson's Handbook of Optical Through the Air Communications.
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AIR TRANSPARENCY MONITOR, XENON FLASH RECEIVER
I designed this circuit many years ago to monitor the quality of a mile long column of air for future optical communications experiments. The transmitter system (circuit 72 below) uses a
powerful xenon flash in conjunction with a large 12 inch fresnel lens at the transmitter end and a matching 12 inch lens with a PIN photo diode at the receiver. The receiver system was connected
to a weather station and a computer to collect the changes in intensity of the light flashes under different weather conditions. It has the potential for a 30+ mile range. I have also used this
system to conduct cloud bounce experiments.
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AIR TRANSPARENCY MONITOR, XENON FLASH RECEIVER, Page 2
This is Page 2 of the receiver circuit above.
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AIR TRANSPARENCY MONITOR, XENON FLASH TRANSMITTER
This is the matching transmitter for the above receiver. The transmitter launches powerful 1000-watt light pulses that last about 20 microseconds.
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- FET INPUT HIGH SPEED LIGHT DETECTOR
This circuit is yet another design that converts current from a PIN photo diode to a voltage. It has a bandwidth that extends beyond 50MHz.
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LASER/LED LIGHT OUTPUT INTENSITY METER
This circuit uses a large 1cm X 1cm silicon PIN photo diode and a transimpedance amplifier to measure the light power output of infrared and visible LEDs and laser diodes. It can be modified to
produce almost any milliwatts to volts scale factor. It can be connected to either a multi-meter or an oscilloscope.
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- LIGHT DETECTORS WITH AMIBIENT LIGHT COMPENSATION
These circuits were taken from a few application notes on infrared remote control devices. They use a current compensation method to separate the modulated light pulses from ambient light. They
appear to have limited bandwidth and may only work at the 30KHz to 50KHz frequencies often used by TV and VCR remotes. I have not yet tested the circuits.
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Light to Frequency Converter
This circuit uses a CMOS version of the classic 555 timer, to form a light intensity to frequency converter. A small PIN photo diode is used as the light detector. The pulses
produced are short, so in some applications you may want to stretch them or feed them through a flip/flop to produce a square wave signal. Although the circuit shown is designed for a 5v
supply, it could operate from almost any voltage from 3v to 15v.
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- LINE POWERED XENON FLASH TRANSMITTER
This line powered xenon flash circuit drives a small camera type flash tube. It has an optical isolator to allow the flash to be safely triggered from some remote device. A flash rate of 2Hz is
possible with the circuit.
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- 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.
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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.
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- 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.
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- 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.
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- 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.
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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)
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- 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.
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| Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:
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| Laser Communication System: This is a simple Laser communication system. It can transmit and receive signal from any audio
device.Communication distance is few meters. All components are not critical. Transistor 2N2222 may be on the coolrib. Laser diode is from laser pointer (Electronic circuit design added 02/05) |
| Laser Link Communicator: audio transmission
up to few hundred meters (Circuit / schematic design added 6/06) |
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