Digital watt meter using pic microcontroller

In this article, I will discuss how to design digital ac watt meter using pic microcontroller. Lets start with basic introduction of watt meter.

What is Watt meter?

Watt meter is electrical device which is used to measure real power in AC circuits and total power in DC circuits. You may have used watt meter in electrical labs. Watt meter most frequently used in electrical labs for performing various lab tasks.

How to measure AC power using pic microcontroller :

AC power is the sum of real power and reactive power. Watt meter is used to measure real power in electrical circuits. As you know real power or active power is the product of voltage, current and power factor of load. So to design AC watt meter using pic microcontroller, you should know how to measure AC voltage, AC current and Power factor using pic microcontroller. After measuring these parameters , one can easily design ac watt meter using pic microcontroller. Real power formula is given below:

P = V * I * Cos(θ)

Where P is real power. V is rms voltage across the load. I is rsm value of current across the load and Cosθ is power factor of load. So to measure active power with the help of pic microcontroller, one should measure above given parameters of real power using pic mcicrocontroller.

How to measure AC current for digital watt meter:

AC current can be measured with the help of pic microcontroller using two methods. one is using difference amplifier and other is current transformer. I have already posted a article on how to measure ac current using pic microcontroller. you can check this article to know about how to measure ac current.

AC current measurement using pic microcontroller  : In this project, I have used difference amplifier and shunt resistor to measure AC current. PIC16F877A microcontroller is used to measure AC current with the help of analog to digital converter. LCD display is used to display value of current on LCD.  Shunt resistor is used a transducers which converts current into voltage. Because microcontroller can not read current directly. Voltage across shunt resistor is measured with the help of pic microcontroller. This measured voltage is again converted back into current using ohm’s law formula. Because value of shunt resistor is known and voltage across shunt resistor is measured with the help of microcontroller. By using  V=IR foruma, current value can be easily calculated with some instructions of programming. I recommend you to read AC current measurement article before going further in this article.

AC voltage measurement using pic microcontroller

• AC voltage can also be measured easily using pic microcontroller. I have already posted two article on AC voltage measure using pic microcontroller. AC voltage measurement using pic microcontroller and Difference amplifier and AC voltage measurement using pic mcirocontroller and potential transformer.    AC voltage measurement using pic microcontroller and Difference amplifier:  In this project difference amplifier is used to step down AC voltage level from 220v AC to less than 5V AC. Because microcontroller can not read voltage more than five volt. Microcontroller PIC16F877A analog to digital converter reads AC voltage and displays it on LCD.
•  AC voltage measurement using pic microcontroller and potential transformer: In this project potential transformer is used to step down AC voltage from 220v AC to 15v AC. After that rectifier is used to convert ac voltage into pulsating DC. Pulsating DC voltage is measured with the help of microcontroller and displays it on lcd.

Power factor measurement using pic microcontroller

To measure power factor with the help of microcontroller, you should know about zero crossing detection using pic microcontroller. Power factor can be measured after measuring time between two consecutive zero crossing detection’s and time Difference between current and voltage wave form. To read more about zero crossing detection and power factor measurement using pic microcontroller, check following articles:

•     Zero crossing detection using pic microcontroller
•    Power factor measurement using pic microcontroller

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