|
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.
.(designed by David A. Johnson) |
|
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.
.(designed
by David A. Johnson) |
|
1us Light Pulse Receiver Plus Post Amp - 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 receiver section of Dave
Johnson's Handbook of Optical Through the Air Communications. (this link is off-site)
.(designed by David A. Johnson) |
|
20MHz VCSEL 3mW Laser Test Circuit - This circuit takes advantage of some new vertical
cavity surface emitting lasers (VCSEL) that dont 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.
.(designed by
David A. Johnson) |
| 30kHz Light Receiver Amp - 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 battery.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
40kHz Light Detector With High Ambient Light Immunity - 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....
.(designed by David
A. Johnson) |
|
40kHz Light Detector with Sunlight Immunity - 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.
.
.(designed by David A. Johnson) |
|
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 current.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by
David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
Air Transparency Monitor, Xenon Flash Receiver, Page 2 - This is Page 2 of the air
transparency monitor receiver circuit.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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 (added 02/05) |
| Laser Light Detector, 10mhz to 20mhz - This circuit was
originally designed to detect laser light pulses for an optical Ethernet communications
system. It has good ambient light immunity.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David
A. Johnson) |
|
Low Power 40kHz Light Receiver New - Drawing only 100uA, this circuit provides high
sensitivity with excellent ambient light immunity.
.(designed by David A. Johnson) |
|
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.
.(designed by David A.
Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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)
.(designed by David A. Johnson) |
|
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.
.(designed by David A. Johnson) |
|
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 rooms walls
and ceiling is usually enough to trigger the circuit. The entire circuit draws only
3 microamps from a 6 to 9 volt battery.
.(designed by David A. Johnson) |
