A Handy Optical Wattmeter

By A. Samiuddhin

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All residential and industrial units have energy meters that show energy consumed by the users. But the power (watts) is not shown by these meters, except by some new models.

During measurement, all energy meters flash an LED at a predetermined rate that is called impulse rate. The common flash rates are 6,400 impulses/kWh, 3,200 impulses/kWh, etc. By using the flash rate and some math, the power can also be calculated.

Presented here is a circuit to calculate the power consumed with the help of pulsing LED light of the energy meter and show it.

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Circuit and working

The circuit diagram of the optical wattmeter is shown in Fig. 1. The circuit includes Arduino Nano board (Board1), 16x2 LCD display LCD1, NPN transistor BC547 (T1), and photo-transistor L14F1 (T2).

Fig. 1: Circuit diagram for optical wattmeter

Whenever the energy meter’s LED light falls on photo-transistor T2, it conducts, thereby activating transistor T1. The pulse available at collector of T1 is given to first interrupt pin (pin D2) of the Arduino board. The Arduino calculates the power consumed in watts with the help of software, which is updated to the LCD display simultaneously.

 

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