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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.
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.
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.
COLOR FILM
MAKES OPTICAL FILTER
This isn’t an electronic circuit but the file shows the curve for an optical
filter made from exposed color film. The material blocks most visible light but
is very transparent to 880nM infrared light. Kodak 100ASA is exposed to "cool
white" fluorescent light for about 5 seconds. Then, the film is developed in the
usual way. The color negatives form the filter material and does a fine job of
blocking visible light wavelength and passing the longer near infrared
wavelengths. Published in Electronic Design, Dec
2, 1996.
Makes Visible
Light Blocking Filter from Color Film Negative
This isn’t an electronic circuit but the drawing below shows the curve for an
optical filter made from exposed color film. The material blocks most visible
light but is very transparent to 880nM infrared light. Kodak 100ASA is exposed
to "cool white" fluorescent light for about 5 seconds.
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.
Pigeon
Scarecrow
I have an area on my roof where a large flock of pigeons like to roost.
Their nesting materials and droppings really make a mess. Often there is enough
junk from them that it clogs my roof gutters. Perhaps one way to scare
them away is with a device mounted on the roof near their favorite roosting
spot. The device....
Reflected Infrared Light Switch Infrared light
reflected off a finger is used to activate this switch circuit.
Drawing only 30uA from a 3v supply, this circuit
will detect a human finger with a range of about 1 inch. The sensor uses
an inexpensive infrared LED and a matching photo diode.
(added 7/06)
Shadow
Activated Motion Detector Circuit
There are many ways one can detect nearby human or object motion. This
circuit demonstrates one way. It detects motion by noting the changes in
the shadow cast by the moving object. The hobby circuit below works quite well
in typical indoor room lighting. I would not recommend its use in direct
sunlight. Two small PIN photodiodes positioned about one inch apart form a
shadow detector. With no shadow cast on the devices, both devices produce
nearly identical current levels. The current is converted to a voltage
with a load resistor in parallel with the photodiode....
Short Range
Reflective Object Sensor
Drawing only 30uA from a 3v supply, this circuit will detect a human finger with
a range of about 1 inch. The sensor uses an inexpensive infrared LED and a
matching photo diode.
TV/VCR Infrared
Remote Booster
This circuit will boost the signal from any infrared TV or VCR remote, extending
the range by a factor of 3X.
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 my
Handbook of
Optical Through the Air Communications.
