Safety Guard

This is a simple circuit of Safety Guard. Protect your home appliances from voltage spikes with this simple time delay circuit. Whenever power to the appliances is switched on or resumes after mains failure, the oscillator starts oscillating and D5 blinks. This continues for three minutes. After that, Q14 output of IC CD4060 goes high to trigger the gate of the SCR through D4. At this moment, the voltage is available at the cathode of the SCR, which energizes the relay coil to activate the appliance and D6 glows. Switch SW1 is used for quick start without waiting for delay.

Safety Guard Circuit Diagram:

Parts	Description
R1	1M
R2	470R
R3	820R
R4	56K
R5	470R
R6	1K
R7	10K
C1	1kuF-25V
C2	100nF-63V
C3	0.02uF-63V
C4	10uF-25V
C5	10uF-25V
D1	1N4007
D2	1N4007
D3	1N4007
D4	1N4148
D5	Red LEDs
D6	Red LEDs
RL1	12V Relay
IC1	AN7809
IC2	CD4060
SW1	Switch
T1	24V-AC Centre Tapped Transformer

Circuit Operation:

At the heart of the circuit is IC CD4060, which consists of two inverter gates for clock generation and a 14-bit binary ripple counter. Here the clock oscillations are governed by resistor R1 and capacitor C1. In this circuit, only two outputs of the IC (Q5 and Q14) have been used. Q5 is connected to an LED (D5) and Q14 is used to trigger the gate of the SCR through D4 as well as reset the counter. The anode of the SCR is connected to +9V and the cathode is connected to the relay coil. The other pin of the relay coil is connected to the negative supply, while its contacts are used for switching on the appliances.

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