- 1 WATT FLUORESCENT LAMP NIGHT LIGHT
If you are tired of replacing small night light lamps, try this circuit. The line powered circuit uses a long life cold cathode fluorescent lamp. A simple charge pump technique runs the lamp without any transformer. - 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. - 12v Light/Dark Lamp Switch
At night, this circuit will route current to a 12v lamp, turning it on. (added 7/06) - 60 Watt Lamp with Auxiliary 14v LED Lamp
This circuit controls power to a standard 60 watt lamp plus generates an auxiliary 14v DC supply which can power an automotive style 12 LED array. (added 7/06) - Incandescent Lamp Inrush Current Limiter
This circuit limits the large inrush current often associated with large incandescent lamps. With the components shown the current is limited to 1 amp, but it could be scaled to any desired current. (added 7/06) - 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 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. - 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. - Laser Used as Vehicular Traffic Counter
This is an illustration how a laser could be used to count traffic and measure the speed of each car passing through the sensor area. (added 7/06) - 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. - Modulated Laser Diode Tester
This circuit can either be used to test laser diodes or as a general purpose modulated light source. The circuit has an adjustable diode threshold current and an adjustable modulation frequency. The frequency can be adjusted from below 30KHz to above 50MHz. It is powered from a 9v battery. - Low Voltage Latching Relay Driver
Using some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source. By using a latching relay, power can be controlled to a load with a tiny battery. - PUSHBUTTON ONESHOT AND LATCH
This circuit uses a single IC to convert a noisy pushbutton switch signal into a clean pulse or a sustained push on-push off signal. It can operate from 3v to 18v. - Ultra Low Power Latching Relay Circuit
The circuit below takes advantage of some inexpensive small super capacitors. The circuit pumps 6 volt pulses into the separate 5 volt latching and unlatching relay coils. A short 25ms pulse is all that is needed to flip the relay states. A third super capacitor is used to supply a higher peak current than a small lithium cell might otherwise be able to supply. - Universal Flasher using Latching Relay: This circuit is powered by a 9v battery and controls any AC to DC load through a set of relay contacts, rated at 10 amps. To conserve power, the circuit uses a latching relay. A variable frequency oscillator controls the flashing speed from 0.2Hz to 2Hz. A pair of pulse generators first latch the contacts closed then unlatches them open. The power consumption is so low that a 9v battery will last for several months.
· 0.5V Negative Supply
Although not very efficient, this simple circuit, consisting of two LEDs and a photo diode, generates a negative voltage with a current level of a couple milliamps. It is ideal for supplying a negative rail to low power “rail to rail” op amp circuits, which need to have a true zero volts output.
· 1 LINE TELEPHONE LINE STATUS INDICATOR
This circuit is similar to the above circuit, but only monitors one phone line.
· 1.5V LED FLASHER VERSION A
Many published circuits that Flash LEDs need 3 volts or more. This circuit uses only a single inexpensive C-MOS IC and Flashes the LED for a full year on a single 1.5 volt AA alkaline battery cell. The circuit uses a charge pump technique to provide the LED the needed voltage.
· 1.5V LED FLASHER VERSION B
To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5 volt alkaline N cell should Flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage.
- 1W White LED Night Light NEW
As many of you know, I have a pet peeve with poorly made LED night lights. Often, the light from the LED quickly fades, so within months, the light is useless. I have posted several versions of modified night lights using higher quality components. This circuit is yet another version, which produces much more light than those other designs. The circuit brings together two high power white LEDs made by Cree with a compact AC to DC power supply from Bias Power..... - Wireless LED Driver NEW
The circuit solves this problem by sending power to the LED through the plastic, using a magnetic coupling technique. The circuit below can route power through plastic enclosures as thick as ¼ inch. The circuit will not work through metal boxes.....
· Wig/wag LED Flasher
This simple circuit will flash two LEDs in an alternating fashion.
· WHITE LED NIGHT LIGHT
This simple circuit is designed to plug into a standard AC electrical outlet. It uses four super bright white light emitting diodes (LED) in conjunction with a capacitor coupled full wave rectifier circuit. The LEDs are mounted in a box and are angled slightly to bounce the light off of a nearby wall. The light should last about 10 years. The circuit draws less than one half of one watt of power and can therefore run continuously. In spite of the low power, the LEDs provide sufficient illumination for most night light applications. Circuit component values for both 120vac and 240vac are shown.
- White LED Night Light using a 1W LED NEW
As many of you know, I have a pet peeve with poorly made LED night lights. Often, the light from the LED quickly fades, so within months, the light is useless. I have posted several versions of modified night lights using higher quality components. This circuit is yet another version, which produces much more light than those other designs. The circuit brings together two high power white LEDs made by Cree with a compact AC to DC power supply from Bias Power..... - Universal 3v LED Flasher
The circuit below will flash any LED color with fixed current pulses powered by a 3v battery. It uses a charge pump approach, which routes a constant current pulse through the LED, regardless of the LED voltage requirement. Using this approach, white and blue LEDs, which normally require about 3.6v can be flashed with a 3v battery. With the component values selected, the LED is hit with 15ma current pulses lasting about 10ms every two seconds. This keeps the average current draw from a 3v battery to about 200uA. The circuit relies on a cheap 74HC14 hex Schmitt trigger inverter IC. One inverter forms a pulse generating oscillator. Other inverters are ganged together to increase the drive current. A two transistor circuit forms a constant sinking current controller. - Ultra Low Power LED Flasher
The efficiency of some newer LEDs is amazing. Some of the latest green LEDs can launch blinding light with just one milliamp of current. I take advantage of one of these newer devices in the circuit below. The flashing circuit uses a classic multivibrator oscillator, made from a tiny National Semiconductor’s LMC7215 low power voltage comparator. The circuit produces a short 10ms pulse every two seconds, drawing power from a 3v supply. I suggest using a surface mounted green LED from King bright..... - Remote LED Indicator Light -- NEW
There are times when you would like to transmit a signal from one LED indicator light to second LED at another location. The circuit below works well for this application. It takes advantage of the fact that the internal infrared LED inside an opto-isolator has a lower voltage drop than the visible LED being tapped into. Using a Darlington type opto-isolator also means very little current needs to be diverted to the isolator..... - Table Lamp with auxiliary 12v Automotive Style LED Light
This circuit provides about one watt of non-isolated DC power for an automotive type 12v LED array lamp in addition to a standard incandescent table lamp. - Universal LED Flasher
This low power LED flasher circuit draws about 100ua from any DC power supply ranging from 3 volts to 24 volts. The 1.0Hz 10ms LED pulsed current is held to a constant 10ma. - Ramping LED Driver
The circuit below was designed to drive a LED with an intensity ramping mode. Two 555 timers generate two different triangle waveforms. The upper device generates a 10KHz signal while the lower unit produces a 1Hz signal. The two signals are fed to a voltage comparator. The result is a pulse width modulation (PWM) signal, which with the aid of the FET, drives the LED in such a way that its average light output slowly ramps from about zero light to maximum and then slowly dims back down. The circuit should operate over a supply voltage ranging from 3v to 12v. You can easily vary the ramping time by changing the value of the 1M resistor. For an interesting effect, you can place a 1N4148 diode in parallel with the 1M resistor, with the cathode (banded end) side connected to pin 3. - Reduced Power Sequential LED Flasher NEW
The 74HC4017 is a neat decade counter which has 10 decoded outputs. When supplied with a low frequency clock and with a LED attached to each of the outputs, an interesting ten step sequential flasher effect can be produced. The LEDs can be configured in a wide variety of patterns of loops, lines or arrows. But, these circuits can often be power hogs. To reduce the average current needed to produce the same effect, you can strobe the individual LEDs with a short 10mS pulse. - High Power LED Flasher
Power LEDs are becoming more popular these days. The DC input power to these devices ranges from 1 watt to 5 watts. Normal LEDs only receive about 0.05 watts. At this higher power, these devices can emit a lot of light. You can buy them in just about any color in the rainbow but white seems to be the most popular. One application for these devices is a flashing light. If the flash duration and flash rate is kept low, the average current can be low enough that even a small battery can last quite a while.....
· Lighthouse LED Flasher
This was originally designed for a model in a HO train set. It simulates the behavior of the light from a lighthouse. The LED intensity gradually increases, then flashes with a bright light and finally decreases slowly in intensity.
· 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.
- Fake Car Alarm Light
Whenever the car’s ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system.
· FLASHING LED POWER INDICATOR DRAWS LOW CURRENT
This circuit Flashes a power indicator LED to keep the average current low.
- High Intensity Line Powered LED Flasher
There are times when you would like to generate an intensely bright flash of light using electrical power from the AC line. The circuit below can drive a one to three watt power LED with about 350ma of peak current. Since the circuit drives the LED with a constant current, any LED color can be used. I have also shown how you could use an array of 7 LEDs, wired in parallel. This array may not produce as much light as the single power LED but the array would be cheaper to build. .... - Battery Charge Current Indicator
This circuit turns on a LED whenever it detects at least 25ma of battery charge current.
· Constant Current LED Driver
Bob Pease from National Semiconductor came up with this circuit and I have used it many times. It maintains a constant current through one or more LEDs. A single resistor controls the desired current.
· FLASHING LED ADVERTISING BADGE #1
I have seen numerous Flashing light badges at trade shows and conventions. They are often handed out as gifts to promote some business. The devices often use inefficient circuits, which cause the battery power source to be quickly depleted. My circuit is simple but efficient enough to provide months of continuous LED Flashing. It also has a tiny push-button switch to turn on and off the light Flashing, extending battery power.
· 2 LINE TELEPHONE LINE STATUS INDICATOR
Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. The circuit is line polarity insensitive.
- 9v Battery Voltage Monitor
This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts. It uses a LTC1440 comparator, which also contains a 1.18v reference diode. In standby mode, the circuit draws only 4uA. - 12v Lamp Current Indicator
This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp.
· 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.
- AC Line Powered LED Pilot Light
This simple circuit can be used to light a LED indicator lamp, powered from the 120vac line. I have included component values for 240vac lines as well. - AC Powered White LED Strings NEW
A while back a guy by the name of Ken Schultz sent me a simple drawing of how he connected a string of 30 LEDs, to make a nice under the counter accent light, powered by 120vac. He wired the strings in two series sections of 15 LED each, but wired in opposite directions. He then used just one capacitor to limit the AC current through the two stings. I looked at the circuit and decided that it seemed quite reasonable. The only change I decided to make was to add a metal oxide resistor in series with the capacitor, to act as fuse and to limit the peak current, should there be a voltage spike on the AC line. With the two strings of 15, the current is first pumped through one series string, then as the AC line polarity changes, it flows through the second string. ... - 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. - 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. - 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. - 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. - 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. - 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. - 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. - 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....
· 40KHz Light Detector with Sunlight Immunity NEW
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.
- 40KHZ LIGHT RECEIVER AMP
This circuit is similar to 30KHZ LIGHT RECEIVER AMP but provides more gain and operates up to 40KHz. However it draws more power supply current. - 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. - 40KHz MODULATED LIGHT DETECTOR
This circuit uses a unique cascade 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 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. - 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) - 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. - AIR TRANSPARENCY MONITOR, XENON FLASH RECEIVER, Page 2
This is Page 2 of the receiver circuit above. - 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. - 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. - 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 - 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. - 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. - LINE POWERED XENON FLASH TRANSMITTER
This line powered xenon flash circuit drives a small camera type flash tube. t 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. - Low Power 40KHz Light Receiver
Drawing only 100uA, this circuit provides high sensitivity with excellent ambient light immunity. - 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 micro amps from a 3 volt supply. - 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. - 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. - 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. - 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. - 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) - 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. - 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 micro amps from a 6 to 9 volt battery. - Dark Activated 12v Power Supply Switch
Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down. (added 7/06) - 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. - 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. - 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. - 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 mill volts per microwatt of 900nm light. - 40KHZ LIGHT RECEIVER AMP
This circuit is similar to 30KHZ Light Receiver Amp but provides more gain and operates up to 40KHz. However it draws more power supply current. - 40KHz MODULATED LIGHT DETECTOR
This circuit uses a unique cascade 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. - 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. - 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. - 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. - CASCODE LIGHT RECEIVER CIRCUIT
This page provides a detailed explanation of how the modified cascade light receiver circuit operates. The cascade technique in conjunction with an inductive load provides very high current to voltage conversion as well as very high speed. - 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. - 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. - 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. - 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. - 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. - 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. - 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. - 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 micro amps from a 3 volt supply. - 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) - 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. - 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. - Photo Transistor Interface Circuits
This page shows different ways to improve the response time of a photo transistor circuit. - 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. - 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. - 40KHz Limiting Amp
This circuit has a gain of X20 at 40KHz. The amplifier output level is limited to 2.5v peak to peak. Limiting action begins with a 50v peak to peak input. (added 7/06) - Incandescent Lamp Inrush Current Limiter
This circuit limits the large inrush current often associated with large incandescent lamps. With the components shown the current is limited to 1 amp, but it could be scaled to any desired current. (added 7/06 ). - 40KHZ LIGHT RECEIVER AMP
This circuit is similar to 30KHZ Light Receiver Amp but provides more gain and operates up to 40KHz. However it draws more power supply current - 3KHz LOW PASS FILTER PLUS AUDIO AMP
This circuit uses a switched capacitor filter IC from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio. The schematic includes an audio amplifier that is designed to drive a standard audio head phone. 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) - AUDIO AMP + 3KHz FILTER
This circuit is the audio amp section for a complete optical transmitter. The circuit amplifies and filters the voice audio signals from an electret microphone. The circuit is described in more detail in the transmitter circuit section of Dave Johnson's Handbook of Optical Through the Air Communications. (this link is off-site) - ELECTRIC FIELD DISTURBANCE MONITOR
This schematic is the power supply and front-end sections of the field monitor that is discussed in more detail at Electric Field Disturbance Monitor. The system can detect human and animal motion by the electric fields they disturb. - LOW PASS ACTIVE FILTER DESIGN COLLECTION
This is a collection of inverting and non-inverting active low pass filter circuits. I included one, two, three, four and six pole filter circuits. You can change the component value ratios shown, to achieve any frequency cut-off you may need. The circuit does not specify an operational amplifier. The circuits should be used to select the needed resistor and capacitor components for a particular frequency knee and roll-off slope.
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