Cuando un peso o una fuerza mecánica actúan sobre el sensor de este circuito, cambia su resistencia y, con ello, puede accionar un relé. El circuito descrito es simple y utiliza una esponja conductora que se utiliza en embalajes de circuitos integrados.

Los circuitos integrados sensibles como los de tecnología CMOS pueden, en algunos casos, venir en envases con una esponja que, cortocircuitando sus terminales impide que sean afectados por descargas estáticas.

Estas descargas, como la de la electricidad acumulada en nuestro cuerpo, podrían quemar el componente por el simple manejo.

En la figura 1 tenemos la forma en que estas esponjas se utilizan para proteger los terminales de un circuito integrado.

 

Figura 1 - Una esponja conductora usada en la protección de un circuito integrado
Figura 1 - Una esponja conductora usada en la protección de un circuito integrado | Haga click en la imagen para ampliar |

 

Una característica interesante de estas esponjas es que si a apretar o aplicar una fuerza en sus caras, ella cambia de resistencia, pudiendo entonces ser usada en un simple sensor, como el mostrado en la figura 2.

 

Figura 2 - Un sensor de presión usando una esponja conductora
Figura 2 - Un sensor de presión usando una esponja conductora | Haga click en la imagen para ampliar |

 

Basta con colocar dos planchas de metal en contacto con la esponja, como muestra la figura para que funcione como un sensible sensor de presión.

En nuestro circuito utilizamos un sensible amplificador operacional para detectar cuando la resistencia cambia y así accionar un relé.

Este circuito se conecta como se muestra en la figura 3.

 

Figura 3 - Conexión del sensor
Figura 3 - Conexión del sensor | Haga click en la imagen para ampliar |

 

El sensor, junto con un resistor de alto valor (que puede cambiar) forma un divisor de tensión que aplica cierta tensión a la entrada del amplificador.

Esta tensión se compara con una referencia ajustada en el potenciómetro P1.

Cuando la resistencia del sensor cambia, el comparador percibe esto y su salida conmuta, accionando un paso amplificador que tiene por carga un relé.

El relé puede entonces ser usado para accionar algún tipo de automatismo, o incluso una alarma.

 

Montaje

En la figura 4 tenemos el diagrama completo del sensor.

 

Figura 4 - Diagrama completo del sensor
Figura 4 - Diagrama completo del sensor | Haga click en la imagen para ampliar |

 

El montaje se puede hacer en una matriz de contactos con la disposición de componentes mostrada en la figura 5.

 

Figura 5 - Montaje en matriz de contactos
Figura 5 - Montaje en matriz de contactos | Haga click en la imagen para ampliar |

 

Observe la posición del circuito integrado y el relé puede ser de tipo que encaje en la matriz de contactos o aún externo.

 

Prueba y uso

Conecte la alimentación del circuito y ajuste P1 a un punto en el que esté cerca del disparo del relé.

Presionando el sensor, el relé debe cerrar sus contactos.

El cable al sensor no debe ser largo para que no ocurra la captación de ruidos que causan el disparo errático.

La alimentación no debe ser hecha por fuente sin transformador.

 

CI-1 741 - Circuito integrado

Q1 - BC548 - transistores NPN de uso general

D1 - 1N4148 - diodo de silicio

X1 - Sensor de presión - ver texto

K1 -Relé de 6 a 12 V según la alimentación

P1- 2M2 - potenciómetro

R1 - 100k ohms x 1/8 W - resistor - marrón, negro, amarillo

R2, R3, R4 - 10 k ohms x 1/8 W - resistores - marrón, negro, naranja

R5 - 4k7 x 1/8 W - resistor - amarillo, violeta, rojo

C1 - 100 uF x 12 V o más - condensador electrolítico

 

Varios:

Matriz de contactos, material para el sensor, hilos, soldadura, etc.

 

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