Iron Box Power Saver

This power saving circuit is used to save electricity while ironing by switching OFF the iron box when it is not in use. Once the  on time of the circuit is crossed, it produces an alarm. If we press the  reset button at the time of alarm, it  is switched off and the  on time of the circuit is extended to the next 4 minutes. This circuit works as a reminder for those who always forget to turn OFF the iron box in  their busy schedule.

In this, the circuit is built around NE 555(IC1), op-amp LM 358 (IC2) and few other components. IC1 is designed as a standard monostable multivibrator and its trigger pin 2,held high by resistor R1.LM 358, is configured as a comparator. It  has both a non-inverting input (pin 3) and an inverting input (pin 2). Inverting pin 2 of IC2 is connected to voltage-divider preset VR1 which aids in varying the reference voltage at pin 2. Buzzer is connected to the output pin 1 which is initially low.

The ‘ON’ time of IC1 is adjusted to 4 minute with the help of capacitor C1and resistor R1. Output pin 3 is fed to the relay driver transistor.

BC 548.

When the switch S1 is pressed, the monostable (IC1) is triggered, the output of IC1 goes high, and the iron box is switched  on through relay RL1. Led2 (yellow) is used  to indicate that the output is  on.

At normal condition, the voltage at the non inverting pin of LM358 (IC1) is less than the voltage at the inverting input of the LM358 and hence the output of the op amp is low.

The timing capacitor C1starts charging and the voltage at the non inverting pin of LM358 (IC1)  gets higher than the voltage at the inverting input of the LM358. So the output of the op amp  is switched to high. This in turn activates the buzzer,  thereby producing a beep sound. If we press the reset switch S2 at the time of alarm, it  turns  off the alarm, and extends the  on time of the circuit to the next 4 minutes. If the reset switch is not pressed at the time of alarm, the iron box is automatically switched  off.

Assemble the circuit on a general-purpose PCB and enclose it in a suitable cabinet. Mount switch S1, S2 and the buzzer on the front panel of the box.

COMPONENTS LIST

IC1-        NE 555

IC2-        LM358

IC3-        7809 REGULATOR IC

T1-          BC548

X1-         TRANSFORMER 230V/12V/500mA

RLY1-     12V 1C/O RELAY

D1-D5-1N 4007 DIODE

C1-   1000MFD/25V

C2-   220MFD/25V

C3-   220MFD/25V

C4-         0.01MFD

R1-      10K

R2-       1M

VR1- 10K PRESET

SW1- ON/OFF SWITCH

SW2, SW3 – PUSH TO ON SWITCH

R3, R4, R5            1K

LED1-                     RED

LED2-                     YELLOW

PIEZO BUZZER