High Level Design

Wireless Ambient Lighting Control System

Pratik Panchal (pp423@cornell.edu), Kedar Vidvans (knv25@cornell.edu)
M.Eng, School of Electrical and Computer Engineering,
Cornell University 

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We had set out to design a lighting system which would act as a constant source of light. This project has a sensor with a photo-resistor which measures the light in the room and transmits it wirelessly to the receiver located with the control panel. We have used Atmega16 at both the transmitter and receiver end as it was a cheap option and our code wasn’t large.The lighting control is done using Pulse Width Modulation on high luminosity LEDs.

The scope of the project covers the development of an Ambient Lighting Solution which will maintain desired luminosity on the focused area. Wireless sensors operating on RF will be used for communicating the current luminosity level. The system will also take care of user defined inputs and hence manual control will also be possible. It will fade out the lights in case no occupancy is detected in the room; thus saving on power consumption and extending life of the lamps.

Higher Level Design:

Source of Idea:

We observed that there is a lot of energy wastage due to improper lighting, due to lights being left on even though there is no one in the room etc. Moreover, incandescent bulbs are also a great source of energy wastage. We have therefore strived to provide a cheap and easy to implement solution. We had originally wanted to only have a light sensor as part of the project, but after hearing our idea Prof. Bruce Land also suggested that we use Passive Infrared Sensor (PIR) to detect human presence in the room.

Logical Structure: The control of the lighting is divided into two parts:

1. Automatic: The control of light is done automatically based on the luminosity measured by the light sensor. This is direct feedback control.

2. Manual : The light measurement of the sensor is decoupled from the light intensity of the LEDs. This mode is provided in case the sensor fails and the user would like to manual control the light using increment and decrement buttons provided on the keypad. 

Figure 1: Block Diagram

1. The light Sensor: This is a Photo resistor whose resistance increases or decreases depending on the light being casted on it. 

2. MCU at Sensor-end: This measures the resistance of the photo resistor and transmits the same via the wireless tranmitter.

3. RF Transmitter: This is a 433 Mhz OOK type transmitter which works on UART.

4. Occupancy Sensor: This sensor measures the Passive Infrared in the room and provides 5 v if it detects infrared above a threshold typically in the region of that emitted by humans. 

5. MCU in Control Unit: This MCU is a Atmega16 controller which receives the light information from the light sensor and produces a PWM to control the luminosity of the LED bulbs.

6. LED bulbs: We had 3 LED bulbs connected in series to a 9 V power supply. The control of the LED bulbs was through a MOSFET and optoisolator connected to the PWM from the Micro Controller.

7. RF Receiver: This is a 433 Mhz OOK type receiver which works on USART.

8. Keypad: The keypad has 2 push buttons to increment or decrement the brightness of the LEDs manually and one toggle switch to set the system in automatic or manual mode.

Hardware/Software tradeoffs:
We have used 433 Mhz wireless transmitter-receiver pair to establish communication between the two controllers. The transmitter and receiver are directly coupled to the micro controller. In order to increase the reliability of communication we could also have hooked them up through a HT12E/HT12D encoder/decoder pair. The encoder/decoder pair  could have been used to establish communication and synchronization with the transmitter and receiver. the encoder/decoder also have functionality to have address of the device hardwired on them, therefore we can have seamless integration with multiple devices through them. But, we had decided to develop this functionality as a software function instead of a hardware chip due to restriction on funds.

Disclaimer: This work has been done as term work for the course ECE4760 Digital System Design using Microcontroller, at school of Electrical and Computer Engineering, Cornell University by Pratik Panchal and Kedar Vidvans under guidance of Prof. Bruce Land. Readers can use the presented work on this site as long as they acknowledge the source. The work is presented in as-is condition and If used, no liability is borne by either the authors or the school.

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