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PRACTICAL EXAMPLES OF THE USE OF RELAYS

V. Ryan © 2002 - 2009

Below are some examples that show how relays can be used as part of a practical circuit. As stated in the first information sheet, the relay is normally used to switch ‘on’ another circuit.

RAIN ACTIVATED ALARM

   

This circuit is simple in its operation, if it rains the relay is ‘energised’ (switched). This could be part of a rain detection system. The rain falls onto a small sensor which allows current to flow from positive to negative. Current also flows into the base of the transistors and the relay is energised. In turn, a second circuit is switched on and the piezo buzzer sounds. This circuit could be used to warn of rain so that the washing could be collected in before it gets too wet.
 

   
 
   

THE ZN 1034 PRECISION TIMER AND RELAY

   

   

The ZN 1034 integrated circuit is a precision timer. It is an extremely useful chip and often is used in conjunction with a relay. In this circuit when the switch is pressed the relay is ‘energised’ for a period of between two and one hundred minutes, depending on how the variable resister has been set. This means the buzzer sounds for that amount of time.

It is a simple task to slightly alter the circuit so that when the switch is pressed the buzzer does not sound until after the set time - a delay has been introduced.

   
 
   

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