Proa

Instead of in series with the input, the resistor R can be connected between pins 1 and 2 of the IC if the load is constant. You can see this in the right figure. This will make some part of the load current flows through the resistor and the other part through the device.

When the circuit at its close state, the IC will control the buzzer time using the resistor and capacitor. The buzzer sounds like alarm in the different frequencies.

•     Resistor R1 : 1.8k ohm
•     Resistor R2 : 1k ohm
•     Resistor R3 : 5.6k ohm
•     Resistor R4 : 480 ohm
•     Capacitor C1 : 2.2 nF
•     Polar Capacitor C2 : 0.022uF/6V
•     IC1 timer : NE555
•     Speaker SP1 : Tweeter 8 ohm
•     Power supply : 5V

The first IC used as a 1 second clock, which generates ON/OFF for the other ICs. Diodes help to cover the IC555 from the peak voltage. Take note that the relay used should have impedance more than 50 ohm.

Parts list :

•     Diode D1-D2 : 1N4001
•     Zener Diode D2 : 6V
•     R1,R5,R7 : 3k3
•     R2,R6,R8 : 68k
•     Resistor variable VR1 : 47k
•     Polar capacitor C1 : 10uF/16V
•     Polar capacitor C3,C5 : 2.2 uF/16V
•     Capacitor C2,C4,C6 : 0.01 uF
•     Transistor T1 : BC107/BC148
•     IC timer : NE555
•     Relay : 6-9 V
•     Power supply 6-9 V