The meter has a (standardised) red LED that flashes once for each watt-hour. The Pi has a phototransistor that turns flashes into a GPIO transition interrupt. I've put it on my solar panel generation meter, and plan to build another (slightly improved) unit to monitor the mains input meter.
The meter has a (standardised) red LED that flashes once for each watt-hour. The Pi has a phototransistor that turns flashes into a GPIO transition interrupt. I've put it on my solar panel generation meter, and plan to build another (slightly improved) unit to monitor the mains input meter.