aCareer Episode-1
Introduction
1.1
(Date: Aug-Nov, 2009)
I did my Bachelor’s degree in Instrumentation and Control Engineering from Dr B R Ambedkar National Institute of Technology which was established as Regional Engineering College and was given the status of National Institute of Technology (Deemed University) by the Government of India on October 17, 2002 A large number of reputed Industrial houses in the country visit the Institution and select the final year students as Engineers/ Management Trainees. As one of the National Institutes of Technology (NIT), the Institute has the responsibility of providing high quality education in Engineering, Technology and Sciences to produce competent technical and scientific manpower for the country. As part of the course I undertook a project to make a system which would detect if a person enters or leaves a room and based on the number of occupants would turn all the electrical appliances of the room off or on.
Background
1.2
India is a rapidly growing economy which needs energy to sustain its growth and despite having huge energy crisis (where power cut is more of a norm than exception) there is still significant power wastage every year. To tackle with this problem, I decided to make Occupancy detection and Power Control Supply system. The target of this project was to reduce the wastage of electricity by turning the power supply to a room off when there is no one to use it, for that we required a way to reliably count how many people were in the room so when the count goes down to zero turn the power supply for the room off and if someone comes in turn it back on. This was an individual project so I was responsible for designing the circuit, Soldering the components onto stripboard pcb, making the code for microcontroller in assembly language, testing the circuit, testing the code and preparing project report
Personal Engineering Activity
1.3
The first step was to decide on the correct sensor to detect presence, since I wanted this system to be cheap and affordable for everyone a motion detector was out of question a decade ago, ultrasound could not have worked either as the shape of room was unknown so I decided on using sensors to detect if someone entered or left the room at the door and keep count. I tried infrared detectors and IR LED’s but they faced interference from sunlight and I wasn’t able to reliably detect if the person was entering or leaving. So I decided on using LDR’s and two laser lights. Depending on which one was cut first I could confirm if someone entered or left the room
1.4
As mentioned earlier, power cut is more of a norm than an exception so I had to ensure the count was kept even when there was no power and if someone left or entered the room during the power cut I had to put in a method to update the details so I used two 7-segment displays to show the current count (assuming the room cannot hold a very large crowd) and two buttons as interrupts for the microcontroller to increase and decrease the count. For the same reason I also saved the program and the count in EPROM.
1.5
There were a few ways to control the power supply of the room, electromagnetic not-gate(relay) which would have required a separate 7-9V power supply was also heavy, big and not an elegant solution, but the one that suited best was power transistor however I faced some issues with it. Once triggered it would not turn back off and I had trouble understanding why. After consulting my supervisor, I found that the power transistor has a very high gate impedance and did not need a resistor to be pulled-down. So I removed the resistor and it toggled as intended.
1.6
I used the LDR’s output through analog to digital converter and fed it into interrupt for the microcontroller and depending upon which one was obstructed first I could deduce to reduce or increase the count and when the count goes to zero pull the pin to the power transistor base down. The 7-segment display was mapped on to different pins of the microcontroller through a resistor to represent the current count. I also had to design the parts to hold LDR’s so as to minimize the noise due to other sources of light. For the lasers I took them out of the metallic shell and built a base to hold them parallel to the LDR’s and at exact distance from each other as the LDR’s and connected to power supply instead of button cells. I also had to remove the button and make them permanently on.
1.7
To design the circuit properly I had to check the voltage and current thresholds of all components circuit segments and add required resistors and capacitors. I had to perform several calculations for both the circuit and microcontroller. I had to calculate the resistance of various parts, the current flowing through each component and voltage allowed for various components and therefore the resistance to be added in series or in parallel to protect them. Once I had completed the diagram I soldered the components in proper places on a stripboard PCB and connected the cables. I asked for help from my classmate who had had experience soldering circuits to teach me how to solder properly and more efficiently. After the circuit was completed I tested it for various inputs and calibrated the LDR set and power transistor voltages for optimal performance.
1.8
Since I had to handle live circuit with 240V I had to take care of safety of me and everyone around me. I had to make sure the circuit was not exposed in any way and the parts circulating 240V were isolated from the rest of the circuit and properly insulated. I had to ensure there was no short-circuit and the load was of appropriate rating. The power transistor had to be soldered properly, insulated and connected to a heat sink with proper ventilation.
1.9
During the semester I would meet with my supervisor every Monday to discuss the progress and any issues I faced. We would also set the scope of the project and adjust deliverables as per circumstances. I would document the methods, design parameters and ideology behind every step which helped me prepare my project report at the end which included details of the circuit design, components used, technical drawings, subroutine program, all the references which I consulted and reasons for using the sensor set and methods I used instead of alternatives and final test results. I also gave a presentation for 15-minute at the end of semester followed by 5-minute Q&A.
Summary
1.10
The project was successfully completed and all objectives were met. The project made me use various engineering skills, electronics skills to design and implement the circuit, Computer science skills to program the microcontroller in assembly language. I learned how to choose correct sensors and to take environment and operation parameters into account while selecting your sensors, and also the cost involved. I also learned how to install the sensor in correct holder as to minimize environmental noise. I learned how to check for component specifications so as to add resistors or capacitors and use that to design a perfect system. I also learned how to learn new skills from colleagues and seniors, my classmate taught me how to properly solder.