DETECTOR DE PROXIMIDAD POR INFRARROJO con dos 555
Es quizás uno de los circuitos de mayor aplicación en el automatismo electrónico. 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 l os 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 util izarla 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 corriente,, en este caso un par de transistores en configuración darlington 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 LM555 1N 4148 2N 3904Lista de materiales
Circuito Impreso 2 circuitos integrados LM 555 2 1 1 1 1 3 2 1 1 1 1 2
bases de 8 pines relé 12 V 5 pines foto transistor de uso general diodo infrarrojo de uso general control de 1 Mega transistores 2N3904 condensadores. de 10 uF/50 V diodo 1N4148 led verde de 5 mm R 68 H Resistencia 1K5 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 Ω Y el foto transistor y los dos transistores darlinton por un foto detector
1 2 3
Ve GND Vout 123
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 l os 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 se muestra 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
Corriente de salida
Temperatura de trabajo
Consumo de potencia
–0.3...6.0 V 5 mA –25...+85 °C 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 b e 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 the y 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 b e 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 pho totransistor (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 ph ototransistor. There are a number of phototransistors sizes and case st yles. 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 pho tocell (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 ma y be necessary when the light falling on the cell is not very strong or shadows can affect the ph otocell. 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 co nductance 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 p hoto-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.html http://home.cogeco.ca/~rpaisley4/ATDetIR.html
Photodiode Light Detector This light detector is a currentto-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.
Photodiodes A 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.
Photodiode The 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.
