Home power consumption measuring unit

From CaveLab
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This module was given to a friend many years ago.
Home power consumption measuring unit complete and connected

Measures the power consumption by counting LED pulses from the home fuse box. Measurements can be read via a serial interface, uses the AVR ATtiny2313 microcontroller.


In Norway we have a LED in our home fuse boxes that flashes a defined number of times per kW, this unit measures the home power consumption by counting those pulses. This is calculated into kW and can be read from a computer over the serial interface. In addition to this unit you will need a sensor to read the LED, that is not covered in this project. It is important that this sensor is accurate to get precise values.



The consumption is measured in kW and calculated by dividing the number of LED pulses by 500 (500 pulses pr. kW). The registration will continue as long as the module receives a signal from the sensor.

Storing values

Two values are stored in EEPROM; current and previous consumption. By sending a command over the serial interface the current value can be moved to previous and cleared. This makes it possible to compare the current period with the previous. Values are written to EEPROM every hour, and restored during boot. This means that in the event of a power loss you could lose up to one hour of monitoring.

On first start up the unit will show -1 kW for both current and previous usage, this can be cleared by moving current to previous two times. Or you can enter a current value manually. Correct EEPROM values will then be stored one hour after the first signal is received.

Reading values

It is possible to use the serial interface directly to read and move consumption values. But ideally an external system, like a computer or Raspberry Pi, could pull values at set intervals. This would make it possible to create graphs and trends over time.



Input pins

  1. PB.0 Sensor

Output pins

  1. PB.1 Run LED
  2. PB.2 Signal LED


Power connector

2,5 mm, 9-12V=, positive center.

9-pin Sensor

  • 6 : 5V + out
  • 7 : 5V - out
  • 8 : 5V + sensor in
  • 9 : 5V - sensor in

9-pin RS-232

  • 2 : Transmit
  • 3 : Receive
  • 5 : GND


Terminal communication

Forbruksmaaler v.1.0                                                           
JensenCorp 0704001                                                             
Press 0 for help                                                               
1 - Current usage                                                              
2 - Previous usage                                                             
3 - Enter starting point                                                       
4 - Move current to previous                                                   
Current usage will be deleted! (0 to cancel)                                   
Enter starting point in kW : 100                                               
100 kW saved                                                                   
100 kW current usage (50000 pulses)                                            
100 kW moved to previous                                                       
100 kW previous usage                                                          
0 kW current usage (0 pulses)

Serial settings

Data bits
Stop bits

Source code

Bascom-AVR source is available in a git repository:


Schematic drawing


Parts list

Sensor not included.
Qty. Part
1 × AVR ATtiny2313-20PU, DIL-20, 20 MHz, 18 I/Os
5 × Capacitor, aluminium electrolytic, 1 µF, 50V
1 × Capacitor, aluminium electrolytic, 10 µF, 25V
2 × Capacitor, aluminium electrolytic, 47 µF, 25V
2 × Capacitor, ceramic, 1 nF, 100V
2 × Capacitor, metallized polyester foil, 10 nF, (0.01 µF)
1 × D-sub cable, pin-to-pin 5m, 9-pin male-female
2 × D-sub soldering cups, 9 pin female
1 × D-sub soldering cups, 9 pin male
1 × DIL socket, 16-pin, 7.62mm
1 × DIL socket, 20-pin, 7.62mm
1 × DIL socket, 6-pin, 7.62mm
1 × Diode, rectifier, 1 A, 400V, 1N4004
1 × Enclosure, plastic (1591 FL), 112x62x31mm, flange
1 × Fuse 5x20 mm, 400 mA, fast-acting
1 × Fuse holder, open, PCB, 5x20mm
1 × Fuse holder, open, PCB, Protective cover
1 × Heatsink, 27.3K/W, 19mm, attachable, TO220
1 × LED 3mm, Green, 2.1V, 20mA, 3.5mcd, 38°
1 × LED 3mm, Yellow, 2.0V, 20mA, 2.5mcd, 38°
2 × LED holder 3mm, Black plastic
1 × Optocoupler, single, CNY17F-3, DIL-6
32 cm2 PCB, stripboard, 100x160mm, 160cm2
1 × Power jack, panel, 2.5mm, plastic housing
1 × Power jack, plug-in, 2.5mm
4 × Resistor, carbon film, 0.25W, 330 Ω, 5%
1 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
1 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
1 × RS232 interface, MAX232CPE, dual
2 × Spacer, round unthreaded, 3mm, Ø6mm, Delrin
6 × Straight pin header, female, Dual row, 2.54mm
9 × Straight pin header, female, Single row, 2.54mm
2 × Straight pin header, male, Dual row, 2.54mm
17 × Straight pin header, male, Single row, 2.54mm
1 × Voltage regulator +5V, 2 A, L78S05CV