Freespace Communications

Light Beam Communications Circuits
Freespace Circuits: #'s - K L - Z

Last Updated: June 02, 2021 01:45 PM

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

Circuits Designed by Dave Johnson, P.E. :

100Khz Low Power 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 . . . Hobby Circuit designed by David A. Johnson P.E.-April, 2005

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

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

1us LED Pulse Driver + Voltage to Frequency Converter - 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 . . . Hobby Circuit designed by Dave Johnson P.E.-March, 1999

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. . . Circuit by David A. Johnson P.E.-March, 2002

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

40KHz Light Detector with Sunlight Immunity - This hobby 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 . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

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

AIR Transparency Monitor, Xenon Flash Receiver - I designed this receiver 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. . . Circuit by David Johnson P.E.-June, 2000

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

AIR Transparency Monitor-Pg2 - This is of the receiver circuit AIR TRANSPARENCY MONITOR, XENON FLASH RECEIVER. . . Circuit by David A. Johnson P.E.-June, 2000

Ambient Light Dectector with 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 30K . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2000

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

Five-Watt 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. . . Circuit by Dave Johnson P.E.-June, 2000

Fluorescent Lamp Intensity Modulator - This hobby circuit was designed to experiment with using small fluorescent lamps as a broad pattern source of modulated light. This hobby 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. . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

High Ambient Light Immunity Light Detector - 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 . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2004

High Ambient Light Immunity with a 40Khz Light Detector - 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 . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

High Speed Light Detector from FET Input - 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 . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Free Space Circuits: #'s - K L - Z