SINGLE IC FORMS SENSITIVE MODULATED LIGHT RECEIVER (15)
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
40KHz LIGHT RECEIVER IS IMMUNE TO AMBIENT LIGHT (16) (40krvr1)
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.
1uS LIGHT PULSE RECEIVER PLUS POST AMP (27) (500krvr3)
This circuit is designed to detect very weak light pulses
lasting 1uS. It uses a tuned LC feedback network to provide high
sensitivity while giving high ambient light immunity. A post
voltage amplifier is included with a gain of about X20. The
circuit is described in more detail in the of Dave Johnson's
of Optical Through the Air Communications. (this link is
1uS LIGHT PULSE DISCRIMINATOR PLUS F TO V CONVERTER (28)
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 of
Handbook of Optical Through the Air Communications.
VOLTAGE TO FREQUENCY CONVERTER + 1uS LED PULSE DRIVER (34)
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
of Optical Through the Air Communications. (this link is
40KHz TV-VCR LIGHT SOURCE REPEATER (35) (40kvcr)
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.
MICRO POWER 40KHz BURST LASER DIODE DRIVER (36) (40klrl)
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.
9v POWERED XENON PHOTOFLASH CONTROLLER (42) (xenflsl)
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.
SIMPLE NITROGEN SPARK GENERATOR (43) (spark4)
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.
LINE POWERED XENON FLASH TRANSMITTER (44) (xen2xtr)
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.
20MHz VCSEL 3mW LASER TEST CIRCUIT (58) (20mhzlsr)
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 MODULATED LIGHT DETECTOR (59) (40krvr2)
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.
40KHz LASER BURST DETECTOR (60) (40krvr3)
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.
10MHz TO 20MHz LASER LIGHT DETECTOR (61) (20mrvr2)
This circuit was originally designed to detect laser light
pulses for an optical Ethernet communications system. It has
good ambient light immunity.
PULSED LED TEST CIRCUIT (63) (testled)
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.
FET INPUT HIGH SPEED LIGHT DETECTOR (69) (fetamp0)
This circuit is yet another design that converts current from a
PIN photo diode to a voltage. It has a bandwidth that extends
AIR TRANSPARENCY MONITOR, XENON FLASH RECEIVER (70)
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
AIR TRANSPARENCY MONITOR, XENON FLASH RECEIVER (71)
This is page two of the receiver circuit above.
AIR TRANSPARENCY MONITOR, XENON FLASH TRANSMITTER (72)
This is the matching transmitter for the above receiver. The
transmitter launches powerful 1000-watt light pulses that last
about 20 microseconds.
5W FLUORESCENT LAMP INTENSITY MODULATOR (75) (5wlamp)
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
LASER/LED LIGHT OUTPUT INTENSITY METER (80)
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.
LIGHT DETECTORS WITH AMIBIENT LIGHT COMPENSATION (83)
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.
OPTICAL RFID TEST CIRCUIT (87) (opiddemo)
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
WIDE BAND ZERO CROSS DETECTOR (109) (zerocross1)
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
40KHZ LED TEST SIGNAL GENERATOR (111) (40khzref2)
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.
XENON LAMP FLASH DETECTOR (112) (xenonflsdet1)
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.
30KHZ LIGHT RECEIVER AMP (121) (30khzamp1)
This circuit uses NPN darlington transistor to amplify the
signal produced from short light flashes, as detected by a PIN
photo diode. The circuit draws only about 330uA from a 6v
40KHZ LIGHT RECEIVER AMP
This circuit is similar to number 121 but provides more gain and
operates up to 40KHz. However it draws more power supply