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Light Dependent Resistor Circuits / Photocell Circuits
Light Dependent Circuits:  #'s - D      E - L      M- Z


Last Updated: October 24, 2017 02:55 PM

Circuits Designed by Dave Johnson, P.E. :

Laser Burst Light DetectorThis 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. . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Laser Light Detyector-10Mhz to 20MhzThis circuit was originally designed to detect laser light pulses for an optical Ethernet communications system.  It has good ambient light immunity . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

LED/Laser Light Output Intensity MeterThis 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 b . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2000

Light DetectorThis 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.  This hobby 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. . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

Light Detector with High Ambient Light ImmunityThis 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.. . . Circuit by David Johnson P.E.-July, 2006

Light Monitor CircuitThe circuit below takes advantage of a low power op amp with a “rail to rail” feature.  The single resistor R1 defines the light sensitivity of the circuit.  The output voltage is directly proportional to the intensity of light striking the small photodiode . . . Hobby Circuit designed by David A. Johnson P.E.-August, 2010

Light Pulse Receiver + Post AmpThis 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. . . Circuit by Dave Johnson P.E.-March, 1999

Light Receiver 30Khz AmpThis 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 . . . Hobby Circuit designed by Dave Johnson P.E.-March, 2002

Light Receiver Front-End CircuitIf 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.  Note: The LF357 operational amplifier is no longer available this circuit is for reference only. . . . Hobby Circuit designed by David Johnson P.E.-March, 1999

Light Receiver Works from 1Khz to Over 70MhzThis 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. . . Circuit by David A. Johnson P.E.-June, 2000

Light Receiver-10MHz to 20MHzLight power to volts conversion = APPROX.15mV per microwatt at 850nM . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Light to Frequency ConverterThis 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 . . . Hobby Circuit designed by David Johnson P.E.-May, 2008

Light/Dark 12V SwitchOften, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day.  Most commercial day/night switches are designed for AC lighting.  The circuit below was designed for a 12v DC system.  But, it could be modified for other voltage as well.  It uses an inexpensive phototransistor as the light detector.. . . Circuit by David A. Johnson P.E.-June, 2008

Line-Powered Xenon Flash TransmitterThis 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. . . Circuit by David Johnson P.E.-June, 2000

Low Power 40KHz Light DetectorThis 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.. . . Circuit by David A. Johnson P.E.-July, 2006

Low Power Amp Monitors LightThe circuit below takes advantage of a low power op amp with a “rail to rail” feature.  The single resistor R1 defines the light sensitivity of the circuit.  The output voltage is directly proportional to the intensity of light striking the small photodiode. . . Circuit by David A. Johnson P.E.-August, 2010

Low-power optical interrupterThis 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. . . Circuit by David Johnson P.E.-June, 2000


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Lamp Flasher -  This circuit adopts the rather unusual Bowes/White emitter coupled multivibrator circuit.  The oscillation frequency is about 1Hz and is set by C1 value.   __ Contact: Flavio Dellepiane, fladello @ tin.it

Laser Burst Light 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. . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Laser Light Detyector-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 . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

LDR light/dark activated relay Switch -  We wanted to do a light/dark switch as a kit.  But we found there were several types of basic circuit.  This is one type of circuit.  Two other types may be found in Kits 79B and 79C.   __ Designed by R. M. Marston

LED Photo Sensor -  Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary LED.  The LED voltage is buffered by a junction FET transistor and then applied to the inverting input of an op-amp with a gain of about 20.  This produces a change of about 5 volts at the output from darkness to bright light.  The 100K potentiometer can be set so that the output is around 7 volts in darkness and falls to about 2 volts in bright light __ Designed by Bill Bowden

LED/Laser 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 b . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2000

Light / dark activated relay -  The potmeter adjust the trigger 'on' level.  The diode in the diagram shows to be 1N914.  This is ok if you have a light-duty relay, also the 1N914 is a signal diode so actually does not qualify.  Use a 1N4001  (Tony van Roon's or better) instead.  A couple of substitutes for the 2N2222 transistor are: NTE123A, ECG123A, PN100, etc __ Designed by Tony van Roon  VA3AVR

Light Activated Relay -  This is same circuit as above with the addition of a photo resistor to trigger the flip flop instead of a push button.  The bias resistor in series with photo resistor was chosen so that sufficient voltage is present at the base of the 2N3904 to supply current to the circuit in ambient lighting conditions __ Designed by Bill Bowden

Light Activated Relay with 555 IC -  This light activated relay circuit presented here uses the 555 timer IC and a light dependent resistor or LDR to form a light sensitive relay in an intruder alarm system or for switching on a lamp at Sun set and off at Sun rise.  Potentiometer R1 value must be chosen and then adjusted that under normal conditions when the light __ Designed by Popescu Marian

Light Activated Siren -  This light activated siren could make an unknowing “victim” wet his pants when turning on the lights in a dark room.  This thing is LOUD! Power into the module is 3W and produces a 123db sound level from its 50mm diameter diaphragm.  It wavers between 2kHZ and 4kHZ.  An LDR senses ambient light level and switches on __ Designed by Jim Keith

Light Dependent Resistor -  Find out more about LDRs and their use in renewable energy projects.   __ Designed by REUK-Renewable Energy UK website

Light Detector -  This circuit detects light falling on the Photo-cell  (Light Dependent Resistor) to turn on the 555 and create a tone that is delivered to the speaker.  Pin 4 must be held below 0.7v to turn the 555 off.  Any voltage above 0.7v will activate the circuit.  The adjustable sensitivity control is needed__ 555-Timer

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.  This hobby 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. . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

Light Detector -  NOTE :  Variable resistor R1 adjusts the light threshold at which the circuit triggers.  R1's value is chosen to match the photocells resistance at darkness.  The circuit uses a CMOS 4001 IC.  Gate U1a acts as the trigger, U1b and c form a latch.  S1 resets the circuit.  The output device may be a low power piezo buzzer. __ Designed by Mick Devine, UK

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.. . . Circuit by David Johnson P.E.-July, 2006

Light Monitor Circuit -  The circuit below takes advantage of a low power op amp with a “rail to rail” feature.  The single resistor R1 defines the light sensitivity of the circuit.  The output voltage is directly proportional to the intensity of light striking the small photodiode . . . Hobby Circuit designed by David A. Johnson P.E.-August, 2010

Light Pulse Receiver + 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. . . Circuit by Dave Johnson P.E.-March, 1999

Light Receiver 30Khz 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 . . . Hobby Circuit designed by Dave Johnson P.E.-March, 2002

Light Receiver Front-End Circuit -  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.  Note: The LF357 operational amplifier is no longer available this circuit is for reference only. . . . Hobby Circuit designed by David Johnson P.E.-March, 1999

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. . . Circuit by David A. Johnson P.E.-June, 2000

Light Receiver-10MHz to 20MHz -  Light power to volts conversion = APPROX.15mV per microwatt at 850nM . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Light Sensing RF Transmitter -  This transmitter is very simiilar to the Simplest RF Transmitter.   The only difference being the photoresistor placed in series with R1.   This could also be a thermistor or other variablwe resistance sensor. __ Designed by Tony van Roon  VA3AVR

Light Sensor Adapter for Oscilloscope -  This circuit is a simple visible light or IR detector for testing any equipment which outputs light. The circuit can be also used for measuring ambient light levels.  This circuit is based on one photodiode which is used in photocell mode so that the photodiode generates a voltage and current signal when it get light.   __ Designed by Tomi Engdahl

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 . . . Hobby Circuit designed by David Johnson P.E.-May, 2008

Light to Frequency Converter -  Fout = –1.4kHz per microampere of photo diode current, IPD.  The LTC6990 is a precision silicon oscillator with a programmable frequency range of 488Hz to 2MHz.  It can be used as a fixed-frequency or voltage-controlled oscillator  (VCO) .  The LTC6990 is part of the TimerBlox family of versatile silicon timing devices.  A single__ Linear Technology/Analog Devices App Note, Jun 16th 2010

Light/Dark 12V Switch -  Often, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day.  Most commercial day/night switches are designed for AC lighting.  The circuit below was designed for a 12v DC system.  But, it could be modified for other voltage as well.  It uses an inexpensive phototransistor as the light detector.. . . Circuit by David A. Johnson P.E.-June, 2008

Light/Dark Detector drives a relay -  This handy little circuit can tell the difference between darkness and light, making it very useful for switching on and off signs, porch lights or other things when it gets dark or light.   __ Designed by Aaron Cake

Lightening Detector -  A VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning.  A bright lamp flashes in synchrony with the lightning bolts indicating the proximity and intensity of the storm.  It has a superior RF section with a single resonance near 300kHz and plenty of sensitivity.  The antenna is a telescopic antenna that extends to two or three feet __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Lightning Activated Camera Shutter Trigger -  This circuit is used to trigger a camera's electronic shutter circuit when a flash of lightning is present.  This circuit would also work for photographing fireworks displays or other events involving flashes of light.   __ Designed by G. Forrest Cook

Lightning Detector -  Egor! Come quick! A storm approaches!   Here is a VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning.  A bright lamp flashes in sychrony with the lightning bolts indicating the proximity and intensity of the storm.  Figure 1 shows the simple receiver which consists of a tuned amplifier driving a modified flasher circuit. __ Designed by Kyriakos Kontakos

Lightning Simulator -  This little simulator generates short pulses at a few Hz rate and is heLPFul in designing and testing lightning detector circuits like the one at the top of the page.  The output is connected to a shielded audio cable with an RCA type connector.  The other end of the cable is connected to the antenna of the lightning detector through a 10 pF capacitor  (not shown) .  The shield of the audio cable is connected to the detector's ground.  The 10 pF allows the lightning detector's tuned circuit to ring and the amplitude of the ring may be observed on the collector of Q1.  The circuit is built into a Home Depot gift certificate can.  The circuit board slides into two card guides glued to the ends of the can.  Any type of construction will probably work fine, but a metal can is recommended to keep the pulses "contained.  " __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Light-Operated Doorbell -  Light-dependent switches are used in automatic hand-dryers and flushers in toilets.  Here is a simple light-operated switch that works in normal light also.  You can affix it on the main door...__ Electronics Projects for You

Light-Operated Internal Door Latch -  Using this light-operated circuit, you can close or open the door of your room remotely from your bed.  You just have to focus the torchlight on the light-dependent resistor of the...__ Electronics Projects for You

Light-Sensitive Alarm -  The circuit detects a sudden shadow falling on a light-sensor and sounds a bleeper for a short time  (adjustable) .  Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor.  Breaking this beam will then cause the bleeper to sound __ Designed by John Hewes

Light-Sensitive Fire Alarm -  This light-sensitive fire alarm circuit is extremely sensitive, low-cost and easy to assemble even by a beginner.  It uses infrared photo transistor as fire sensor.  Circuit and working Circuit diagram of the light-sensitive...__ Electronics Projects for You

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. . . Circuit by David Johnson P.E.-June, 2000

Low Power 40KHz Light Detector -  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.. . . Circuit by David A. Johnson P.E.-July, 2006

Low Power Amp Monitors Light -  The circuit below takes advantage of a low power op amp with a “rail to rail” feature.  The single resistor R1 defines the light sensitivity of the circuit.  The output voltage is directly proportional to the intensity of light striking the small photodiode. . . Circuit by David A. Johnson P.E.-August, 2010

Low-power optical interrupter -  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. . . Circuit by David Johnson P.E.-June, 2000

   <<<         This the last page of EL

Light Dependent Circuits:  #'s - D      E - L      M- Z

 


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