Energy meters are standard installations in both residential and industrial settings, providing users with information about their energy consumption. However, the majority of these meters, except for a few newer models, do not display power in watts. Instead, they utilize a predetermined impulse rate to flash an LED during measurement, such as 6,400 impulses/kWh or 3,200 impulses/kWh. Power consumption can be readily calculated by using this flash rate in conjunction with some mathematical calculations. Presented here is a practical optical wattmeter circuit designed to calculate and display the power consumed by utilizing the pulsing LED light from the energy meter.
Circuit and working
The circuit diagram for the optical wattmeter is depicted in Figure 1. It comprises components such as the Arduino Nano board (Board1), a 16×2 LCD display (LCD1), an NPN transistor BC547 (T1), and a photo-transistor L14F1 (T2).
As the LED light emitted by the energy meter reaches the photo-transistor T2, it becomes conductive, subsequently triggering the activation of transistor T1. The pulse generated at the collector of T1 is received by the first interrupt pin (pin D2) of the Arduino board. Utilizing software, the Arduino performs power consumption calculations in watts, and the results are simultaneously presented on the LCD display.
The Arduino Nano board is programmed using the Arduino IDE to compile and upload the program OpticalWattmeter.info. Select the appropriate board from the Board->Tools menu in the Arduino IDE, then COM port and upload the program using the computer’s standard USB port.
Due to the use of the millis library, there may be some variation in the wattage readings. If a more precise result is required, replace the resonator in the Arduino board with an ATmega328 chip with an external crystal and use the inbuilt hardware timer.
Construction and testing
An actual-size PCB for optical wattmeter is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on PCB, enclose it in a suitable plastic box.
Before mounting the Arduino on PCB, do not forget to upload the program on Arduino Nano board. Install photo-transistor L14F1 on the front panel such that it can capture the blinking LED light from energy meter.
This circuit was created for a 6400 impulses/kWh energy meter. This is something that can be adjusted in the program.
This circuit simply requires a single-phase supply. The circuit can be customized with a small OLED display and fitted inside an enclosure similar to that of a non-contact thermometer due to the low component count (Fig. 5).