Light Sensing

Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down...

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 rooms walls and ceiling is usually enough to trigger the circuit. The entire circuit draws only 3 Microamps from a 6 to 9 volt battery...

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...

This circuit is designed for detecting infrared light modulated at around 40KHz. Its feedback scheme cancels much of the DC component from ambient light. Its conversion factor is about 100 millivolts per microwatt of 900nm light...

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...

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...

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...

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...

This is the matching transmitter for the air transparency monitor receiver. The transmitter launches powerful 1000-watt light pulses that last about 20 microseconds...

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...

This circuit is designed to detect the narrow 1uS pulses produced by the above amplifier circuit. The clean logic type pulses produced by the discriminator are then sent to a frequency to voltage converter. The circuit is designed to process a pulse frequency of 10KHz that is frequency modulated by voice audio signals. The circuit is described in more detail in the receiver circuit section of my Handbook of Optical Through the Air Communications...

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...

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...

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...

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...