An Automated Greenhouse Neil Kaul 7/9/01

Transcription

1 An Automated Greenhouse Neil Kaul 7/9/01 INTRODUCTION June 1-30 of 2001, I attended a course on "Machine Architecture and Assembly Language Training" at Mr. Born s house. The purpose of the course was to further my understanding of what happens at the machine level of a microchip circuit. This is a report of my final project for that course. For my final project, I constructed a greenhouse with a heater, lights, and a water pump that are all completely automated by my Rigel R-31JP. The heater works on a closed loop where a sensor continually feeds back information to the processor. The processor turns on or off the heater in order to keep the desired temperature that the user has defined. The lights work on a twenty-four hour clock, and are set to turn on and off on the hours set by the user. The pump is also set on a timer to turn on and off for a duration and frequency defined by the user. Figure 1 Block Diagram of Greenhouse Subsystems

2 HEATER The first thing I worked on was the circuitry and software to control the heater and sensor. I wired up an analog to digital converter (ADC0831) chip to an LM34 temperature sensor, and a small resistor, which acted as a heater, inside a film bottle (see figure 2). Since the 5 volts coming from my board was not enough to significantly overheat the resistor, I had to use a 2N222A transistor to control an external 9-volt power supply. This allowed me to run 9 volts through the resistor without damaging my processor. When I wired it up with the higher voltage, the resistor smoked and generated heat. I then wrote a small program to interpret the signal from the ADC, convert it to degrees Fahrenheit, and turn on or off the resistor according to a value that I set as the desired temperature. Figure 2 Circuit diagram depicting how I used a transistor to control a 9- volt circuit with a 5-volt circuit Figure 3 - Film Can With Temperature Probe and Heating Element

3 An interesting problem came when I tried to apply my new circuit to a real heater. Both the heater and lights that I wanted to drive required 110 volts. That was more than I could control with a transistor. This was disappointing, and I was considering using symbolic resistors and LED s in place of a heater and fluorescent lights. Then, after some research, I read about solid-state relays. They allow a small current to control a high current without physically connecting them. I bought a couple of solid-state relays and wired them into a light-socket box that could be plugged into a wall (see figure 3). This allowed me to control two 110-volt circuits with my Rigel R-31JP. Once I had the solid-state relays, I plugged in my heater, and my control lead, and it worked like a charm. Figure 4 - "Hockey Pucks" Used For High Voltage Controls LIGHTS The next thing I worked on was the light fixture. The difficulty with this program was the math to convert oscillations in microseconds into hours, and programming the processor to just sit there for hours at a time. The system oscillates at MHz and the internal divider of the processor is 12, so I figured that each clock tick seen by T0 or T1 is 12/11,059,200 seconds, or 1.085us. T0 is using a 13 bit counter to count the ticks, so it will overflow after 2^13 (8192) ticks at 1.085us per tick. Through this math, I can expect an interrupt from T0 every 8.888ms. To get a 1 second timer, I had to make my program count 112 interrupts (112 * ms = seconds). The margin of error is half of 1% (( ) / 1.0), but it is close enough for my purposes. When it overflows, it goes to the interrupt vector, where it checks to see if it has interrupted 112 times yet. If it has, it increments a variable that counts seconds. When the seconds variable reaches 3,600, it increments a variable that counts hours, and resets seconds to 0. I also created some variables that let the user tell what time they want to turn on and off their lights on a 24-hour clock.

4 When I had both the heater and lights working, I wanted to run them together. Then I realized that I had a choice. The first choice was that I could program it so that Timer 0 was used for the lights, Timer 1 was used for the pump, and a forever loop was used to constantly check the heater. The second choice was to set up a multitasking environment that would coordinate all three tasks, plus any more tasks that may some day come in handy. I chose to do the added research and work up a multitasking system. I found that most of the complexities of multitasking were already taken care of in a library called RTMT (Real-Time MultiTasking), provided by Rigel. So I started installing my alreadymade functions into tasks. I added some code that printed out the values of variables as the program was running so I could debug it easier. This caused my seconds to speed up significantly. I remembered that the serial port initialization required a timer in order to send and receive information over the serial connection. I had to decide whether to try to figure out how to make the multitasker wait until the command was done, or to debug my program with the increased speed of my seconds. I chose to finish debugging and took out the serial port initialization. This solved the time speed problem. PUMP For a system of water, I planned on sprinkling the plants from the top, using a small pump, and draining the water out of a hole, back into the water source from which the water could be drawn. When I went looking for a pump, I wanted one that was small, and ran on as few volts as I could find. I found an Attwood V500 bilge pump at Wal-Mart that ran on 12 volts. This was still a small problem, because my R-31JP can t handle 12 volts. I referred back to the 2N222A-transistor setup and used it in conjunction with a 12-volt power supply, and tried it out. It didn t work. The 2N222A transistor that I was using couldn t handle the 1.5 amps that my pump required. I had to find another way. Upon realizing that we didn t have a transistor capable of handling such current, Mr. Born was kind enough to lend me his solid-state relay, which could power my pump. With the new circuit in place, I added a task to my program that ran the pump. Because the pump was too powerful for my little sprinkler to run on all 12 volts, I had to program it to turn the pump on and off very quickly in order to get the desired water pressure. When I had the run section of the pump task programmed, I simply put it in a loop that modulated the hours with a userdefined variable that controlled how many hours between watering sessions. Before I took this course, I understood higher-level programming, but not what made it work. With my new understanding of machine language, I can see how devices all around me are controlled. I also now understand the inner workings of a higher-level language, and realize that some errors can be avoided by understanding what each of your commands is really doing. This class has lead to my further understanding of languages themselves, and compilers. It has given me a strong base of knowledge to grow from.

5 Now, I ve got a completely automated greenhouse that regulates heat, light, and moisture. With this, anyone could have a true green thumb. Figure 5 - Water Pump in Action