Help on using 12v relay to control 5v voltage alarm circuit

[jhchong]

hi all,my question is how is the connection of a 12v relay to control a alarm circuit?

basically im using a PIC to give the relay a signal.it means when there's an error or maybe warning it will only activate the alarm circuit.assume the signal given to the relay is logic 1.

the alarm circuit is shown as below.this circuit works under 5v~15V,it means when voltage is supplied,it will activate it straight away.but i dun want it to work that way,but instead of using a relay to control it as said above.

appreciate for help

 

[Andy1845c]

Do you simply want to put the relay in place of the on/off switch in the schematic you posted?

That would be very simple to do. Have you used a relay before?

You won't be able to use a 12v relay directly from a PICs I/O port though. A PIC can't supply 12 volts or more then 25 mA.

You could look for a very small 5v relay that uses less then 25 mA to activate, or use a transistor or MOSFET insted.

 

[audioguru]

A transistor with a series base resistor can be driven by the PIC and the collector of the transistor can control the reset pin of the second 555 that has a pullup resistor. Then the transistor performs like a low current relay.