The following is a method to allow day and night detection using Infrared/Visible light sensitive phototransistors and a simple LM339 voltage comparator circuit. A phototransistor is mounted between the rails so that it is covered by the train as it passes. A system widely used in model railroading. For daytime operation the room lights would be on and when the train blocks this light the train is detected. However when the room lights are dimmed or turned off for night operation, under normal conditions the phototransistor would go dark and act as if it was covered by a train and give a false detection.

The sensors used are silicon phototransistors and Cadmium Sulfide (CdS) photocells. Both of these sensors allow less current to flow when they are dark than when lighted. Phototransistors change their conductance while photocells change their resistance depending on the intensity of the light falling on them. All of the detectors on this page use LM339 Quad or LM393 dual voltage comparator integrated circuits to detect the change in voltage across the sensor. For information on Voltage Comparators please see the Voltage Comparator Information page at this site.

The circuit on this page is for a simple light detector circuit board that has 8 detectors that can be used with visible or infrared light systems. The detectors use LM339 voltage comparators as the active element. Phototransistors or CdS photocells can be used as sensors for this circuit. If phototransistors are used the circuits can also be used as infrared light detectors. These detectors can be used as part of other light detector circuits shown on other pages at this site such as these Light Activated Detector Circuits at this site.

The following is a method to allow day and night detection using Infrared/Visible light sensitive phototransistors and a simple LM339 voltage comparator circuit.

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.

My first project after assembling an electronic design lab was to build a flash trigger that I could use for high-speed photography. I thought it would be useful to share not only the finished product but also the reasoning that went into its design — in the hopes that others will learn from and improve upon it. When I first thought about building a flash trigger, I did some research to see if anyone had a ready-made schematic available. It turns out that Johannes Eriksson has done just that — and kindly provided a schematic and a brief overview of the circuit. I pored over the circuit until I had a tentative understanding of how it worked, then set about designing my own. Since our circuit will use 5V all over the place, our first task is to turn a 9V battery into the voltage we need. Maxim’s MAX603 linear regulator is a handy chip that will output 5V given a wide range of input voltages — with a few supporting capacitors, the chip will do all the work for us. I simply followed the suggested circuit in the datasheet.Next, I needed a circuit that would output a change in voltage when a light beam is interrupted. I turned to Jameco for an infrared LED and matching phototransistor. Fairchild Semiconductor has a good application note about designing with phototransistors — essentially, a phototransistor allows current to flow only when light is present.

In solar cell array applications and solar instrumentation, it is desirable to monitor the approximate position of the sun to allow efficient automatic alignment. The Ll4Gllens can provide about 15° of accuracy in a simple level sensing circuit, and a full hemisphere can be monitored with about 150 phototransistors. The sun provides "" 80 mW/cm2 to the L14Gl when on the centerline. This will keep the output down to,; 0.5 V for f),; 7.5°. The sky provides "" 0.5 mW/cm2 to the Ll4G1 and will keep the output greater than 10 V when viewed.

This simple amplifier will work well with just about any phototransistor. The 741, although designed to operate with a split supply,

A variable resistor is used to vary the light-level response of a phototransistor. Phototransistors are more light sensitive than photodiodes,

Have you ever wanted to make a line following robot but the infrared sensors were too expensive for you Do you want to upgrade the robot in my other instructable Also, if you`re from the UK and have a maplin store near you, you`ll be able to get some IR transmitter and receivers for 99p (They`re side facing LED/phototransistors, so you can have

This circuit is designed to provide an inexpensive way to create a High Impedance Voltmeter while making use of an inexpensive analog or digital multi meter. The circuit is specifically designed for testing phototransistors. This the figure for the circuit; When measuring voltages in high resistance circuits the resistance of the voltmeter itself

For phototransistors a value of 470K ohms will work for most room light situations. If the light is dim, selecting a higher value resistor such as 1 Megohm will give better sensitivity. This High Impedance Test Voltmeter circuit can also be used for testing phototransistors installations. For CdS photocells it is usually best to install the cell

The circuit on this page is for a visible and infrared light detector circuitboard that has 8 detectors. LM339 voltage comparators are the active element. These detectors can be used as part of other light detector circuits shown on other pages at this site such as these Light Activated Detector Circuits at this site. For phototransistors a valu

Below is the circuit I`m working with; I plan on having the infrared phototransistor pairs inserted in 3 locations in the middle of the maze, including the end point. The width of the maze will be small enough for one finger to be able to slide in it, and as both fingers pass the phototransistors, they will cause a sound to be emitted from the spe

I have had several people say that my house number is difficult to read at night. The number consists of four digits mounted on a structural column that holds up a section of my roof. In response to these complaints, my wife has asked that I install some sort of light for our house..

This line follower robot use the following module: Proximity sensor: 8 pcs of phototransistors; ATMega16 Microcontroller; Motor driver L298; C Programming language

This optical trigger is a general purpose module for use with `standard` 3mm package infrared diode emitters and corresponding matched phototransistors. The emitter terminal on the module will source about 27mA to ground with a 1. 2 V drop across the diode. The detector terminal will source a maximum of 3. 4 mA to ground (short circuit). The circuit

Electronics Tutorial about Light Sensor including Photocells, LDR, Photodiodes, Phototransistors, Photovoltaic Cells and Light Dependent Resistor..

JFET input. PN photodiodes such as the popular "bullet cell" put out an extremely low-level signal. Yet photodiodes offer advantages over phototransistors. For example, more rapid response to motion. Also, some photodiodes have a peak response in the range of visible light. On the other hand, most phototransistors provide peak response in the infrared. For color reproduction, flat visible light response is essential.

Build a two-color camera and a three-color monitor. You can build your camera to pick up any two of the additive primary colors. Just install the proper color filters over the phototransistors or photodiodes. With a matrix circuit and an inverter, you will derive the third color. The trick You might not have thethird color, but you can create its complement.