Optical

Optical switch detector with 555

When the phototransistor is stroken by IR light it conducts and the voltage between the 1Mohm resistor(arbitrary) and the phototrans drops from VCC to lower values. When the voltage drops lower than VCC/3 the 555 is triggered and goes high (from 0 TO VCC). The amount of light that strike the phototrans necessary to bring his collector to VCC/3 is determined by the resistor (Vdrop = Icollector * R , so , if Vdrop= 2*VCC/3, the resistance needed to set the threshold on current is R=2*VCC/(Icollector*3)). ..

Photocell Amplifier

The output of the amplifier is to be measured on a digital voltmeter. Besides being able to accept 20 na to 200 micro amps and output voltages that range form 100 mv to 2 or 3 volts, the amplifier needed to have a low input resistance so the diode could be run at or near zero bias so that its output would be a linear function of light on the photocell. It also has to have plenty of connectors. Along the bottom of the board in the image above, from left to right, are a power input connector because it would use an isolated unregulated DC power supply that is sometimes used for other things, a voltage output connector so that its output could be plugged into a digital voltmeter, and an input connector so that it can accept current from a variety of photodiodes...

Light Switch with 555 Timer

When the phototransistor is stroken by IR light it conducts and the voltage between the 1Mohm resistor(arbitrary) and the phototrans drops from VCC to lower values. When the voltage drops lower than VCC/3 the 555 is triggered and goes high (from 0 TO VCC). The amount of light that strike the phototrans necessary to bring his collector to VCC/3 is determined by the resistor (Vdrop = Icollector * R , so , if Vdrop= 2*VCC/3, the resistance needed to set the threshold on current is R=2*VCC/(Icollector*3)). High sensibility phototrans would need a smaller resistor, and weaker phototransistors higher value resistor, you can also use a trimmer to set the on threshold level with precision. The 555 is proved to be the most versatile and ubiquitous IC all over the world.This is a possible use: simple inverting schmitt trigger...

IR Motion Detector alarm

This type of motion detector uses the same basic concept as the active infrared motion detector. An interruption in a 5 kHz modulated pulsating beam that is transmitted by an infrared diode and received by an infrared transistor sets off the alarm...

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 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...

You use your eye to take in the actual light, and the instrument gives you a variable light source for comparison. Right now, the measurements are relative and uncalibrated (that is, no reference to any physical units). It is possible to calibrate the visual comparison photometer, and the people who used them in Canada in 1977 developed a calibration method, but I have not reproduced this...

The circuit in Figure 1a forms a simple light detector that latches and turns on an LED when the ambient light exceeds a preset limit determined by potentiometer P1. LED D1 is both the indicator and the light detector...

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...

This page shows different ways to improve the response time of a photo transistor circuit...

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...

This page features basic, visible light photo-detector circuits that can be used to detect trains. These methods would normally be used with the photo sensor mounted between the rails...

This circuit converts infrared light into sound. Modulated IR light, like that from remote controls, IR received by the phototransistor and is amplified by the LM386 IC. The IC in turn drives a small 8 Ohm speaker...

This page presents information on infrared - `Across The Track` train detection circuits. The circuits are designed around the LM339 comparator chip and can use a wide assortment of matched infrared - emitter / detector pairs...

The circuit in Figure 1 controls the intensity of the artificial light in a room and monitors the temperature of two zones. The two main circuit blocks are the PIC16C67 master controller and the ADT7516 temperature-sensor interface, which includes a four-channel ADC and a quad voltage-output DAC...