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Freespace Communication Circuits, Page 3
(Light Beam Communication Circuits)
Circuits designed by David Johnson, P.E.
Last Updated on:
Friday, March 12, 2010 12:08 PM
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Dave's FreeSpace (Light Beam) Communication
Circuits:
Page 1,
Page 2, Page 3,
Page 4 |
- 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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- 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. t
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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- Low power 100KHz
Light Receiver
By starving a high speed logic inverter for current,
this circuit can produce a sensitive 100KHz light receiver circuit, which is immune
to ambient light, but only drawing 100 microamps from a 3 volt supply.
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| Dave's FreeSpace (Light Beam)
Communication Circuits: Page 1,
Page 2, Page 3,
Page 4 |
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More Freespace Communication
Circuits
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