This is the most recent project I have worked on for my Wireless Systems class. It was a very difficult class with more material that time, but in the end we all had a general understanding of how wireless systems work. This report is on the effects of ground planes on a six element Yagi-Uda Antenna. This was my first real IEEE conference format report, and I'm proud of how it turned out. If you have any suggestions on how I could improve my technical writing or formatting, I welcome the input. A link the paper pdf can be found here: Effects of Ground Planes on a Six Element Yagi-Uda Antenna.
In the course of one of my classes, Electronics Design Lab, my partner, Alex Mault and I saw the chance to improve upon the design of our robot, affectionately named Geoff. Our goal was to take a messy breadboard and make an easy to use PCB from it. The result of our efforts worked remarkably well (meaning it worked exactly the same as before) and reduced the area of the circuit by two-thirds.
Figure 1: Our original, messy breadboard.
Figure 2: The beautiful, simple PCB copy.
The circuit we planned to replicate was a motor encoder feedback system, which uses the optical encoder output of a 10 V DC motor to maintain a constant angular wheel speed. Below is the block diagram of this system for the right and left wheels of our robot, which are independently regulated by a microcontroller (Arduino).
While Geoff (our robot) is in motion, it's motor encoders output a 50% duty cycle square wave with a frequency proportional to the speed of rotation. For more information on Optical Encoders and how to build one, check out my previous post here. This square wave is sent to a 555 chip, set up as a one-shot circuit. A one-shot circuit outputs a pulse of fixed width on every rising edge of the input. Since the input of the one-shot 555 varies, but the pulse width (T_on) is fixed, we can achieve a variable duty cycle output. This output is fed into a voltage amplifier which regulates the ~3V input into a 5V output.
The speed control block is where all the magic happens. First, the output of the voltage amplifier is put through a basic RC circuit. What this does is create a primarily DC voltage with amplitude proportional to the duty cycle of the input signal. This DC voltage can be described as the "current" state of the motor.
For a moment, consider the robot ascending a slope. Given a constant voltage and current input, the robot would tend to slow down. By slowing down, the duty cycle output of the one-shot 555 decreases, and the DC "current" state of the motor decreases. If we use a voltage follower, where the reference voltage is given by a microcontroller to be either high or low, we can pull the dropping "current" DC voltage higher, which maintains the speed of the wheel equal to the reference voltage.
The packages we used were TL272 (Op-Amp) and LM555(One-shot 555). These are shown in the block diagram above.
To create the PCB that replicated this system, we first constructed a fully functional breadboard circuit. Taking these values, Alex created an EAGLE schematic and board layout. I then proceeded to hand make a two-layer board, which turned out to be a very tedious, but ultimately rewarding process, as the board worked just as planned.
I was doing my Calculus 3 homework, which involved finding second and third order taylor approximations and their error bounds for a two variable function, and was getting tired of taking so many partial derivatives.
As an aid, I wrote up a Mathematica program which, when given a function of two variables, point on the function, and error bounds |x-x0| <= dx and |y-y0| <= dy, outputs the taylor approximations up to third order and the second and third order error bounds.
Edit: I recently added the graphs and the FindMaximum function to show at what points where the |f_xx| , |f_yy|, and |f_xy| achieve their maximums within the bounds of error.
My most recent project was spurred from a lecture in my electronics design lab class. The goal of the class is to create a autonomous robot that preforms a unique function. The robot consists of two driving wheels and a castor stabilizer wheel in the rear. Autonomy would be a relatively simple task for a micro controller. But there's a catch, in this class we must construct our own circuitry from the ground up. A type of component we are given are optical encoders, one for each wheel, which are used for speed and distance calculations.
Simply put, an optical encoder is a device that converts the angular position or motion of a shaft or axle to digital code. As shown in the figure below, a light source is shone through a rotating disk with a code track. If the disk is in a position such that the light source can shine through a code track hole, the photodetector puts out a high or low voltage, depending on the circuit.
As the disk revolves, we start to see a square wave form. Note that a 50% duty cycle waveform, or a waveform that is on for 50% of the time, is produced only when the the code track has evenly spaced holes of equal parts hole and blocking material.
This sort of device seemed simple enough to replicate, so a week after that lecture, I sat down with some cardboard, a DC hobby motor, a bright red LED, and a photoresistor, to see what I could come up with.
As a prototype, I created a very basic cardboard box and disc. After connecting the disk to a DC hobby motor and running at high RPM, I foresaw an issue. Due to the inaccuracy of cutting with scissors, the center of mass of the disk was not at the axle. This resulted in a very unstable spin. Complications also occurred when testing the bright red LED and photoresistor. When I flashed the LED at the photoresistor and probed the output, the flash was indistinguishable from the ambient light in my dorm room. At least, it wasn't giving me the nice square wave I was looking for.
The solution was to use an infrared emitter and receiver pair. To mediate the center of mass problem of the disk, I choose to construct a box and disk using a laser cutter, which is far more accurate than scissors.
Once constructed, the laser cut disk and IR emitter/reciever system worked beautifully, producing the pulse wave I was looking for. In my finished encoder, I only used four holes approximately 5mm wide at 0, 90,180, and 270 degrees. This produced a 90% duty cycle.
While this project was simple enough, it took a bit of time to work out some of the kinks. The end product was worth the effort, and I can now make calculations to determine the angular speed, frequency, and inertia of the disk. At least to me, this is quite exciting.
If you have any suggestions on how I might improve this design, please fell free to comment below!
Also, there are reasons we have web-controlled power supplies. One of those reasons is attached below.
-John "I was scared for my life filming this" Dunn
I'd like to take the opportunity to look back on one of my favorite construction projects, the extended bed loft, remembered fondly by most as "4th West".
First, a bit of background on the project. When my friend and I first moved into the dorms freshman year, we had big plans to create a truly epic room setup. Even at the summer orientation, we had taken measurements of the room and sketched a few ideas of how to improve it's design. As it stood, the was fairly spacious. Vaulted ceilings, multiple windows, and standard furniture (desks, drawers, etc.) all allowed for inherent creative layouts. We toyed with ideas like making a knee high platform for our desks or a raised shag carpet area where we could put a conch and TV. Through brainstorming, we realized that our ideas were bigger than the square footage of our dorm. Our first thought to remedy this was to bunk our beds.
In most dorm rooms, the beds are set on university provided frames without any notches or attachment points for bunking. The only hint that bunking might be an option are four 1/4" holes atop each bed post. This means that to loft a bed, one would have to buy and cut metal rods into about 3" sections which could connect stacked bed frames. The benefit to lofting beds include a more open floor space, increased storage, space for activities, and a sense of juvenile spirit. Downsides include the danger of falling out of a high bed, subpar structural integrity, and fire code violations.
While a McGyver'd bed railing might have been a guard from fall protection, my roommate and I thought it best to construct our own, structurally safer, more extensive, lofting system. This would solve our square footage issue and grant us the opportunity to make something unique in the dorm system.
The design we settled on would take advantage of the vaulted ceilings in our room, which reached up to heights of roughly 14 feet at the peak. The blue shaded are of the block drawing below, expertly crafted in Excel, shows the part of the room we proposed to construct a platform with 8' clearance.
Top-Down View
The black line represents the scale outline of the room.
The blue shaded region shows the area lofted.
The four rows on the bottom are unshaded because of an overhang.
As a side note. It would be interesting if somebody who is actually knowledgable on such topics would critic our work. We are always looking to improve.
Neither my roommate nor I had any formal construction education, but throughout the years we had picked up on most of the standard practices from other projects. The goal of the design was to create a lofted area for our beds in the vault of the ceiling. Later on in the project we would add a half level "terrace" in the 4'x8' area not covered by the loft. This would serve as both a place to put our desks and as a step up to access the bed area.
With a final design in mind, we set about making technical drawings. Initially, we hand drew our structure on you guessed it, engineering paper left over from the previous day's calc homework. In an effort to be a bit more professional, we asked a mechanical engineering major to replicate our shoddy drawings in CAD.
Once we got all the materials together, we started actual construction. Because of the width of the stairwell in our dorm, we had to take out the window screen and feed the 12' 2x6's up from the ground outside. The length of these boards also posed an interesting challenge in maneuvering skills inside the room. We started by erecting the six 4x4 posts and screwing them into a rectangular frame on the top. Next we laid out joists that would support any weight placed on top of the structure. The last step was to add 1/2" plywood flooring to the top and supporting braces to the posts. After a few homey touches, we had a finished product.
However, the fun did not stop there! After news of our extravagant lofting system had spread throughout the dorm, we starting hearing from our University. We had expected this, as a large wooden structure in university housing has the tendency to be attract fire code violations. In preparation, we had gone through the housing handbook and reviewed the fire code. In the strictest sense, we were only breaking one rule, which involved the minimum proximity to the sprinkler heads. To show we were willing to do anything to keep our new loft, my roommate and I wrote up a formal 18-page proposal and submitted it for review by the university. Four weeks and a visit from the director of facilities later, the university deemed the structure not to code and ordered that it be removed.
Over the course of this project we learned many things. Not all of which were engineering and construction. Understanding the proper rules and regulations of the space you working with is just as important as the project itself. Even if you do something super cool, like 4th west, the rules are in place for a reason. If something happened, the consequences can always be magnified ten fold. That being said, we wished with all of our hearts that it could have stayed.
-John "It was like rolling out of bed...onto a shag carpet bed" Dunn
I am a sophomore electrical and computer engineering major at CU Boulder. Over the almost two years I have been here, I, along with others, have embarked on a number of fun, outlandish projects. From constructing a loft in my dorm room (That story later...) to hacking through electronics projects like digital clocks and LED cubes, the diversity of projects gone through is limited only by my friends' and my creativity and determination.
The purpose of this blog is to show you what myself and others have been working on recently. If you have any suggestions for projects, please let me know! I love diving into new topics and projects head-first.
