attiny85 based kwh-meter RST -^- VCC TX - - SCK READ - - MISO GND - - MOSI Connect to a cp2102 or pl2303 cable: VCC (5V) to attiny85 VCC (3.3 or 5.0 volt) RX to attiny85 TX (ttl levels) GND to attiny85 GND Wire the following sensor: VCC --- 1K Ohm Resistor --- ATTINY READ PIN --- LDR Resistor --- GND Then log everything from a system (pc/router/embedded board) serial port and then put the data into rrdtool or something equivalent.