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Atmel’s 90E24 is a high-performance active and reactive energy metering device for single-phase two-wire, single-phase three-wire or anti-tampering active and reactive energy meters. Here is a demo power line monitor project using Atmel 90E24 and allows voltage, current, true power, apparent power, reactive power, power factor, phase angle, and line frequency to be accurately measured.
AC power line monitor using Atmel 90E24
Electricity meters usually have blinking LED lights whose flashing rate is associated with the amount of energy usage. This example shows how to use a 555 timer chip acting as Schmitt trigger combined with a phototransistor or LDR to sense the flashing LED on the electricity meter for monitoring electricity usage.
555 timer as power meter
The output of the 555 timer chip is connected to one of the GPIO pins on the Raspberry Pi. A Python script (executing in the background) recording 555 events is calculating actual energy usage [e.g. Watt] every time the 555 is signaling and stores epochs in an SQLite3 database. From this, another Python script (executed from e.g. cron) generates all kinds of energy usage information (e.g. kWh or kWday or whatever). Using Node.js (running on the same Pi) all data is ‘RESTified’ enabling spreading out to the W3. To maintain privacy JSON web tokens are required every time the service is queried. Oh, and there is also a Pimatic plugin available (here)
Electro-Labs new tutorial project is a PIC microcontroller-based digital power meter that will let you measure the power consumption of an electrical appliance connected to the 230V/50Hz mains line. The project implements a resistor-divider network to scale down the mains voltage and then uses MCP3202 ADC chip to convert the scaled AC voltage to digital counts. For current measurement, the ACS712-30A hall-effect sensor is used in conjunction with another MCP3202 chip. The digital outputs from the ADC chips are then read by the PIC18F252 microcontroller for computing the power. The measured AC RMS voltage, current, and Watts are then displayed on the dot matrix LCD. The beauty of this project is the meter itself is powered from the mains, thus avoiding the need for an external power source.
PIC-based AC watt meter
This project uses Atmega168 microcontroller to compute the power usage at home and logs it to an SD card. It has a graphical LCD display too that shows the power usage as a strip chart. Besides, the voltage and current waveforms can also be displayed on the LCD.
The current is measured using a pair of current transformers whereas the voltage is measured using a 2000:1 voltage divider network. An LMC6484AIN quad op-amp and an AD623AN instrumentation amplifier are also used for signal amplification from the current sensor and the voltage divider. Read more
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