- 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.
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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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- 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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- 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.
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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 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.
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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 (AIR
TRANSPARENCY MONITOR, XENON FLASH TRANSMITTER) 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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- Charge Coupled MOSFET Relay
This circuit acts as an AC/DC relay with a rating up to 50 volts peak and up to 10 amps of current. The differential oscillator supplies voltage to the gates of the two FETs with
good isolation will drawing only 1.5ma of current.
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CHARGE COUPLED BI-DIRECTIONAL POWER MOSFET RELAY
The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to
drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power
to a load.
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- CIRCUIT PROTECTS FROM BATTERY POLARITY REVERSAL
This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device
to the battery only when the polarity is correct. The circuit shown was designed for a device powered from a single 1.5 volts button cell battery. However, the circuit will
operate with higher voltages as well.
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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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- High Impedance JFET Buffers
I have used these circuits many times. They are great when you need a low gain AC signal amplifier with a very high input impedance. It is good to 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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- N-CH AND P-CH TRANSISTORS FORM PUSH-PULL DRIVER
This circuit can produce high speed output signals with fast rise and full times. The unique change pump action allows the voltage of the upper P-ch device to range from millivolts to
hundreds of volts. The output current is only limited by the rating of the transistors. I have used this circuit beyond 2MHz.
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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 new
products section.
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- 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.
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- 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.
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- 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.
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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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