Numbers can Empower us to reduce the world's energy consumption,

but before we can change the world, we must first change ourselves.


Here is an example of the kind of visual feedback that Numbers Empower provides users:

This is the power usage of the three sensors that were running during the day of presentations. You can see the usage change as the devices were turned on or off during the day. For most of the day, the space heater was running in fan mode, averaging less than 30 watts. However, you can see that during our demo at 4:10 PM, the usage spikes. This was done to demonstrate the amount of energy used when the heater was turned on the low setting, over 960 watts!

Play around with the graph a little. You can click and drag to highlight an area to zoom in on. Mouse over points to view the data point information. If you want to return to the original view, push the 'clear' button.


Device Name kWh Used Estimated Cost Estimated Monthly Cost
Fan 0.35 kWh $0.06 $1.79
LED String lights 0.13 kWh $0.02 $0.67
Space Heater 0.24 kWh $0.04 $1.23

You can also choose which devices are shown by checking or unchecking the devices on the table above. This table shows the total kilowatt hours used over the graph and estimates the cost based on $0.17061 per kWh. From this estimate, the table also calculates the estimated monthly cost of running that device.

   
   

About Us

Placed 3rd in the 2010 Northeastern ECE Capstone Design Competition

This project was developed by five Electrical and Computer Engineering seniors at Northeastern University. The motivation for this project came from a shared interest in sustainability and reducing carbon emissions. The NumbersEmpower Project will provide a means for consumers to identify their individual consumption habits, and make informed decisions to more efficiently control their usage and reduce their demand. While the project was inspired by existing products, we felt that no existing product offered a complete solution. Our goal was to expand functionality, empower users through live usage, feedback and cost estimation tools, offering complete control to the consumer.

The project includes:

  • Power electronics and conditioning
  • Voltage and current sensing circuitry
  • Zigbee wireless communication
  • User control through customized web interface
  • Visual feedback
  • Non-invasive system implementation
  • Mobile application
Capstone Team Picture

Software Team:

Hardware Team:

Advisor:

  • Bahram Shafai

If you have any questions about the project, feel free to email us

Individual Device Sensor:

The individual device monitor senses the current and voltage signals going to the load appliance and this data is then transmitted to the router for power calculations. The device being monitored is first plugged into the receptacle on the monitor and then the plug on the monitor is plugged into the wall. A voltage transformer steps down the voltage from the 120 VRMS (340 V peak-peak) to lower levels, and then a full wave rectifier diode bridge creates DC voltages. Then the voltages are further reduced by positive and negative 3.3V regulators for the rails of operational amplifiers later in the circuit. A current transducer also takes in voltage from the mains and outputs a sinusoidal voltage signal that is a scaled down signal in-phase with that of the current going to the device under test. Both the current and voltage signals are centered about 0V, however the input signals to the XBee radio have to be in the 0 to 3.3V range. Both signals are therefore shifted into this range by centering the voltage signals about 1.65V. This is done with a voltage level shifter op-amp circuit. Finally the output signals go through buffer amplifiers with unity gain and then into the inputs on the XBee radio.

Controllable Devices:

In addition some of the device monitors include a solid state relay to remotely control current to the device being monitored. The XBee radio can send a control signal to the relay to engage it and allow current to flow to the device.

Household Sensor:

The house level monitor contains similar circuitry to the device monitor, yet uses an AC current transducer to sense the current through the live wire going into the fuse box. The circuit uses the same voltage transformer and level shifter op-amp circuit. The current transducer outputs a voltage difference across two wires. Since this voltage's negative reference is not with respect to the same ground as the voltage transformer the signal goes through a differential amplifier circuit to bring this reference back to ground and center the signal about 0V. This signal then goes through the level shifter circuit for input into the XBee radio.

The voltage signal in the device monitor and the current signals in both the device and house level monitors are then converted to digital values in the ADC on the XBee radio chip and are boosted back up to their actual values in software.