Ambient Energy Monitor: Technical Exercise

23 Feb


The post explains the process of developing early stage prototype energy monitors that record the energy (current) being used through a plug adapter and use an ambient display to provide the user with the information (energy usage). The objective at this stage is to establish communication between energy usage of an appliance and some form of output(display).

The project aims at making people more aware of a cause of an environmental issues and therefore motivating them to control/change the cause of the issue or at least educate them about the issue (e.g making people more aware of the amount of energy being used in their homes to motivate them to control and reduce the energy used). For example by giving them a better understanding of what appliances use the most energy and by making them feel like their actions are visible.

Feedback is an established method of reducing energy usage and motivating people to make changes. But not just domestic energy usage this is just an example, it can be used to promote awareness and therefore motivate change or educate people with regard to any environmental issue.

Part 1

A CT Sensor is used to capture the value of the current flowing through the adapter. A voltage divider is then used to create a voltage that can be read by the Arduino that is proportional to the current flowing through the adapter. Using formulae in a sketch uploaded to the Arduino board I can then calculate the current and print it to the serial monitor.

Part 2

In order to create an ambient display that could be used for further investigations I wanted to be able to control a motor/pump/light etc that has a voltage higher than 5v, using the data from the CT Sensor. In order to do this I would need to use a transistor because the Arduino can only be used to power an appliance between 0-5v. When doing this I had to use an external power supply (a battery that matches the voltage of the motor/pump/light etc.). For this prototype I used a 6v bulb and a 6v battery.  The transistor then allowed me to control the brightness of the bulb using the data from the CT sensor. I also used a rectifier diode which is very important if I decide to follow-up the prototype and use a motor instead of a bulb. This will protect the transistor from back voltage generated when the motor shuts off or turned in the reverse direction.


Part 1

Below is a schematic of how the voltage divider works with the CT Sensor in order to collect the energy usage data and send it to the Arduino.

Voltage Divider with CT Sensor Schematic

Voltage Divider with CT Sensor schematic

Part 2

The data from the CT Sensor is sent to the transistor that then controls the brightness of the bulb. I used the diagram below but replaced the potentiometer with my CT Sensor and the motor with my bulb. I then combined the two circuits to make the Ambient Energy Monitor.

Fig. 1

Below is a picture of the Voltage Divider (as shown in schematic above) wired to the Arduino using a bread board (Fig. 2) and the full circuit(Fig. 3)

Fig. 2: Voltage Divider and CT Sensor

Fig. 3: Full Prototype

At this stage it is just a technical exercise but below are video demonstrations.

Initial comparisons between the use of light with that of a fan identified some interesting properties of both modalities. The fan can appeal to auditory, visual and even tactile senses while the use of light appeals only to the visual and requires the user to look at it in order to receive the information. My research would suggest that if the information is to be provided in the domestic setting then it would be more suitable if it could appeal to the auditory sense or at least more than one.

The disadvantage of the fan is that a small value of energy consumption is not enough to get the fan moving. In my experiment I had to multiply the value of the flow of current so that switching a single light on and off would affect the fan. The problem with doing this is that even if only two lights are turned on the fan will be moving at full speed. With the fan, the different levels of notification are harder to distinguish between. When the fan is moving at speed and then gets faster it is difficult to see and in fact it is the noise of the motor getting louder that provides the information. In order to be able to visually see the difference between two lights turning on and off I had to use the full range of the fan from fully off to full speed. However with the bulb it is different. Even a small current such as a single light turning on and off can be displayed and visually identified. The use of light could display the difference between a number of appliances being switched on and off. The bulb allows more levels of notification to be applied.


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