DETECTOR DE PROXIMIDAD POR INFRARROJO con dos 555

Es quizás uno de los circuitos de mayor aplicación en el automatismo electrónico. Lo encontramos en los dispensadores de agua automáticos, los secadores de mano automáticos y con algunas variantes lo encontramos en las puertas automáticas de los grandes almacenes.

Principio de funcionamiento

Generamos una ráfaga de pulsos de alta intensidad con el LM555 (Cto 1) a baja frecuencia y los transmitimos por el led de chorro infrarrojo (IR). Luego los recibimos en un fototransistor colocado de tal manera que solo los reciba cuando un objeto refleje los pulsos.

Luego procesamos esa señal para poder utilizarla en el encendido-apagado de nuestros aparatos.

Para ello colocamos un fototransistor de tal manera que cuando haya una superficie que refleje los pulsos, bien sea una mano, un objeto cualquiera, a una distancia de unos 10 cm, este los pueda recibir y enviar a un amplificador de corriente, en este caso un par de transistores en configuración darlington.

Cuando esta débil señal alcanza una intensidad suficiente, debido a que se acercó un objeto, entonces logra disparar un temporizador de unos 10 segundos construido con un LM555.(Cto 2)

Luego colocamos una interfase a transistor para alimentar un relé de 12 V 5 PINES, el cual nos servirá para controlar el aparato que queramos.

Hojas de datos

LM5551N 41482N 3904Lista de materiales

1 2 3

Circuito Impreso2 circuitos integrados LM 5552 bases de 8 pines1 relé 12 V 5 pines1 foto transistor de uso general1 diodo infrarrojo de uso general1 control de 1 Mega3 transistores 2N39042 condensadores. de 10 uF/50 V1 diodo 1N41481 led verde de 5 mm1 R 68 H1 Resistencia 1K52 Resistencia 10K

El circuito anterior pude ser realizado utilizando un foto detector

Se sustituye el relé por un diodo led y una resistencia de 220 ΩY el foto transistor y los dos transistores darlinton por un foto detector

1 Ve

2 GND3 Vout

En el mercado existen otras alternativas tanto de la misma compañía como otros fabricantes.Sharp también proporciona otros receptores de infrarrojos como por ejemplo los IS1U621, similares a los aquí utilizados pero con mas rango de recepción (8 metros frente a los 5 de los IS1U60). De otros fabricantes se destacan los PNA4602 o PNA4612 de Panasonic, los LTM-97DS-38 de LiteOn o los SFH5110 de Siemens. En esta comparativa puede encontrarse información adicional sobre las prestaciones de unos y otros.Aunque los pines diferente entre los distintos fabricantes y deberá consultarse en el dataste correspondiente antes de realizar cualquier conexión, en todos los casos nos vamos a encontrar tres patas: una que conectaremos a Vcc, otra que lo haremos a GND y una tercera, Vout, por la que obtendremos diferentes niveles si se recibe o no la señal infrarroja (en el caso de los Sharp, un nivel alto si no se recibe la señal infrarroja modulada o un nivel bajo si se esta recibiendo). Tal y como semuestra en la figura 2, con el IS1U60 visto de frente, las patas de izquierda a derecha corresponden con Vout, GND y Vcc.

con esto se puede realizar la barrera infrarroja utilizando un control remoto

TSOP1738 es un mini-receptor para ser usados en sistemas con control remoto infrarojo. El mismo soporta casi la

totalidad de los codigos de trasnmision. La señal de salida puede ser aplicada directamente a un pin de entrada de un

microcontrolador.

Características principales

Foto-detector y pre-amplificador en un único encapsulado

Compatibilidad TTL y CMOS

Salida en activo bajo

Bajo consumo eléctrico

Alta inmunidad a la luz visible

Soporte para trasmisión continua de datos en velocidades de hasta 2400 bps

Características técnicas

Tensión de alimentación      –0.3...6.0 V

Consumo de corriente         5 mA

Tensión de salida       –0.3...6.0 V

Corriente de salida          5 mA

Temperatura de trabajo       –25...+85 °C

Consumo de potencia          50 mW

Frecuencia de la señal portadora (infrarrojo)

TSOP1730   30 kHz

TSOP1733   33 kHz

TSOP1736   36 kHz

TSOP1737   36.7 kHz

TSOP1738   38 kHz

TSOP1740   40 kHz

TSOP1756   56 kHz

 

Diagrama en

bloques interno del

sensor

Foto y distribución

de las patillas del

sensor

(clic para ampliar)

Basic Visible and Infrared Light Detectors  This page features basic, visible light photo-detector circuits that can be used to detect trains or other light blocking objects.  The sensors used for these circuits are silicon phototransistors or Cadmium Sulfide (CdS) photocells. Both of these sensors allow less current to flow when they are dark. (Phototransistors change their 'conductance' while photocells change their resistance depending on the intensity of the light falling on them.)  The phototransistor or photocell would normally be placed between the rails in the circuits on this page.  The Photo-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.  All of the circuits on this page are configured to have the LED's turn on when the sensor element is dark (covered by a train.) The LED's can also be made to turn off when a train is detected. This will be explained in the NOTES sections of this page.  The supply voltage for the circuits is specified as regulated 12 volts DC but this can be changed if needed. In some cases the values of some resistors may have to be adjusted to compensate.

- Section 1 -

Visible Light Photo-Detector Circuits

Basic Phototransistor Detector

  In this circuit, when the light falling on the phototransistor (Q1) is blocked, its conductance will decrease and the voltage across Q1 will rise. When the voltage rises above 1/2 of the supply voltage the output of the comparator will turn ON and the LED will be lit.

Basic Phototransistor Detector  The only critical part of this circuit is the value of resistor R1 which in most cases can be 470K ohms but may have to be increase if the room is dark or decreased if the room is well lit.  Increasing the value of R1 will cause the sensitivity of the sensor to decrease. This may be necessary when the light falling on the cell is not very strong or shadows can affect the phototransistor.  There are a number of phototransistors sizes and case styles. The smaller cases will be easier to hide but connecting wires may be more difficult.

Basic CdS Photocell Detector

  In this circuit, when the light falling on the photocell (PC 1) is blocked, its resistance will increase and the voltage across PC 1 will rise. When the voltage rises above 1/2 of the supply voltage the output of the comparator will turn ON and the LED will be lit.

Basic Photocell Detector  Due to wide variations in CdS photocells it is usually best to install the cell and then measure its resistance under normal lighting conditions. A resistor with a value that is approximately 3 to 5 times the measured resistance of the cell is then selected for R1. For example; If the cell resistance is measured at 400 ohms then a 1200 to 2200 ohms resistor would be used.  Increasing the value of R1 will cause the sensitivity of the sensor to decrease. This may be necessary when the light falling on the cell is not very strong or shadows can affect the photocell.  This circuit can be adapted for use in dark areas by placing a small light above the photocell.

- Section 2 -

Infrared Light Photo-Detector Circuit

Basic Phototransistor Detector  In this circuit the light falling on the phototransistor will be from an Infrared Light Emitting Diode (IrLED) but otherwise it is the same as the phototransistor circuit shown above.  When the light falling on the phototransistor (Q1) is blocked, its conductance will decrease and the voltage across Q1 will rise. When the voltage rises above 1/2 of the supply voltage the output of the comparator will turn ON and the LED will be lit.

Basic Infrared Detector  For information on calculating the value of current limiting resistors for the IrLED please see the Current Limiting Resistor Calculator page at this site.  Follow this link for more information on this type of detector see: Across The Track Infrared Detectors.

Is The IR LED Working?  Infrared light is not visible to the naked eye, however, a digital camera can be used to view the IR light if it does not have an IR blocking filter on the lens.  The image may not be very bright but close-up or in a darkened area the light should be visible on the camera's display screen.

- Section 3 -

A Practical Quad Photo-Detector Circuit  The next circuit is for a practical 4 photo-detector circuit using an LM339 Quad comparator IC. Although phototransistors are shown, photocells could also be used with the corresponding change in values for resistors R1 through R4.  This circuit can also be used for infrared detector circuits as shown above.

Quad Photocell Detector

  The values for resistors R7 through R10 can also be changed depending on the required LED current. For information on calculating the value of current limiting resistors please see the Current Limiting Resistor Calculator page at this site.

  A printed circuit board with 8 comparator type photo-detectors can be seen at this link. 8 Photo-Detector Circuit Board

  This High Impedance Test Voltmeter circuit can also be used for testing phototransistors installations.

Phototransistor Detector Relay Driver

  By adding a PNP transistor to the basic detector circuit larger currents can be controlled. In this example a small relay is operated by the detector.

Relay Driver

Using Multiple Phototransistors

  More than one phototransitor can be connected to a single voltage comparator. This would allow transistors to be placed along a section of track to indicate when a train is anywhere in that section.

  As long as the train is long enough to cover two sensors the circuit will continuously detect the train.

Multiple Sensors

  Circuit 2 on the schematic is simpler but the phototransistors must have better lighting than Circuit 1 to get good results.

LM339 Data sheet - National Semiconductor (.pdf)

LM393 Data sheet - National Semiconductor (.pdf)

Pinout Diagram For Various Devices.

Please Read Before Using These Circuit Ideas  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.http://home.cogeco.ca/~rpaisley4/PhotoDetectors.htmlhttp://home.cogeco.ca/~rpaisley4/ATDetIR.html

Photodiode Light Detector

This light detector is a current-to-voltage converter. The FET input op-amp prevents the loading of the photodiode and the voltage at the output is proportional to the current in the photodiode. So long as the photodiode response to the light is linear, the output voltage is proportional to the light falling on the photodiode.

PhotodiodesA photodiode consists of an active p-n junction which is operated in reverse bias. When light falls on the junction, a reverse current flows which is proportional to the illuminance. The linear response to light makes it an element in useful photodetectors for some applications. It is also used as the active element in light-activated switches.

PhotodiodeThe mechanism of the photodiode is like that of a (miniaturized) solar cell. Their response time is fast, on the order of nanoseconds. As light detectors, they are reverse biased - the reverse current is linearly proportional to the illuminance striking the diode. They are not as sensitive as a phototransistor, but their linearity can make them useful in simple light meters.

Photodiode Characteristics

The reverse current through a photodiode

varies linearly with illuminance once you are

significantly above the dark current region.

Current to Voltage Amplifier

A circuit for converting small current signals (>0.01 microamps) to a more easily measured proportional voltage.

By the current rule:

so the output voltage is given by the expression above.