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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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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 my Handbook of Optical Through the Air Communications. Note: The LF357 op amp is no longer available, this
circuit is for reference only. |
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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. |
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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 Light Detector with
High Ambient Light Immunity
This circuit is designed for detecting infrared light modulated at around 40KHz. It’s feedback scheme cancels much of the DC component from ambient light. It’s conversion factor is
about 100 millivolts per microwatt of 900nm light. |
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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. |
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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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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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BROAD BAND 2MHz OPTICAL FIBER
RECEIVER
If you need more sensitivity than the above circuit this circuit provides about ten times more gain. It too is designed around an inexpensive plastic optical fiber detector. |
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BROAD BAND 50MHz OPTICAL FIBER
RECEIVER VERSION A
If the above circuit it still too slow, you can try this circuit. What it lacks in sensitivity it makes up for in speed. The circuit attaches a plastic fiber optic PIN photodiode assembly to a
small box containing a small 3v battery and a standard BNC plug. When the box is plugged into to the input of an oscilloscope with a 50-ohm termination resistor, it can detect light pulse
frequencies beyond 100MHz. |
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BROAD BAND 5MHz OPTICAL FIBER
RECEIVER
This circuit is a simple broad band light detector that uses a very inexpensive IC and a PIN photodiode that is packaged for use with plastic optical fibers. It has a bandwidth from 1KHz to
over 5MHz. It is great for experimenting with various modulated light sources. |
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CASCODE LIGHT RECEIVER CIRCUIT
This page provides a detailed explanation of how the modified cascode light receiver circuit operates. The cascode technique in conjunction with an inductive load provides very high
current to voltage conversion as well as very high speed. |
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Clear Fluid Detector
This circuit detects when a clear fluid is inside a piece of clear plastic tubing. It can be used for fluid level control and monitoring. |
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Clear Fluid Detector -2
Using an ultra low power technique, this circuit detects when a clear fluid is inside a piece of clear plastic tubing. It can be used for fluid level control and monitoring. |
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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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HONEYBEE COUNTER
I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive. The low power circuit uses a slotted opto-sensor to detect
the passing bees. The circuit advances an electronic counting module whenever a honeybee passes through the sensor. The device only counts the number of bees going through the sensor. A
different circuit would be needed to count the number of bees only going out or only coming into the hive. |
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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 RECEIVER WORKS FROM 1KHz TO
OVER 70MHz
This circuit uses one tiny C-MOS inverter IC to form a modulated light receiver with a very fast response. It is designed around a PIN photo diode that is packaged for use with plastic optical
fibers. It can be used as an optical fiber receiver. By using the open end of the optical fiber it can "sniff" out any modulated light signals. |
- Modulated Light Monitor
This battery powered circuit will work from DC to 500KHz. It is designed to connect to an oscilloscope to monitor the light level changes and modulated signals. (added 7/06)
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OPTICAL INTERRUPTER DRAWS
MICROAMPS
This circuit is great for battery-powered systems that use slotted type optical interrupters. It draws only 10uA from a 3v battery that should allow up to 5 years of operation from a lithium
battery. |
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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 products
section. |
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Photo Transistor Interface
Circuits
This page shows different ways to improve the response time of a photo transistor circuit. |
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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 a 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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TIME TO DUST INDICATOR
I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough. I have not yet built and tested this circuit
completely but in concept it should work. The circuit draws very low current from a +3v battery and could be housed in a package similar to a small ashtray. The assembly might be placed in a
suitable out of the way area to collect dust. It would alert a maid when it was time to dust the room. The circuit detects dust with an infrared LED that is pulsed so its light shines onto a
smooth flat plate. Any dust settling onto the surface is detected by a phototransistor, mounted at a 90-degree angle from the LED. When the dust reaches a particular level, sufficient light is
reflected into the phototransistor to change the logic state of the circuit to an alarm condition. The alarm output could be connected to a beeper, a flashing LED or to one of the LED flashing
circuits in this hobby circuit section. |
- Xenon Lamp Flash Amplifier
This circuit has a very low standby current requirement yet has very high sensitivity toward the light flashes from a xenon lamp. When connected to a
flip/flop it can serve as an on on/off Controller.
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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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- 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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- 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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