Christina Holman | Design Blog

The printed circuit board design is a projection of the schematic design. The placement of the footprints for the set of jumpers was positioned intentionally to allow for the power lines to be connected simultaneously as well as for easy access when soldering. We went through several iterations in design due to mishaps in communication -- a key issue in engineering firms. It took me a little while to understand just exactly how Battat envisioned this project and the best way to design such. At first, different components were in place than in the final design: I moved from three-way jumpers that resembled the slapstick original design for the Electronics Lab (without direct input into the rails); to long rectangular flow mirroring the circuit schematic; and to a dual-pin jumper and stacked 805 footprints. Finally, I ended with a reasonable and compact design for the PCB power supply. OSH Park, a community printed circuit board order, charges $5 per square inch of a dual-layer bo...

For Fall 2014, I decided to continue my work under Professor James Battat with the dark matter detector and he suggested doing so under PHYS250H -- an independent study in the Physics Department -- in order to receive credit for it. However, the project portion of the course veered from work with the PCB I created earlier and towards design of a PCB power supply for his Spring class PHYS310 "Experimental Physics." The power supply was needed for an Electronics student lab,  where a five-pin DIN draws in four voltage levels of +12V, -12V, +5V and GND for a solderless breadboard. The PCB I designed would use this connector to draw in the four voltage levels, filter for overcurrent and allow direct input into the rails of a solderless breadboard. At the beginning of the process, Battat and I create a concept diagram demonstrating the overall flow of the power supply and, from it, a rough circuit diagram was generated. Over time, the schematic changed with additional and...

Demo Day was a huge success!  The night before, Griffin and I were able to see the final product and discuss what to work on/test for a brief moment, and I was able to get there before the scheduled presentation to clean up a previous team's remnants and prep our own product. Griffin and I were able to test a spiral design on a few sheets of paper on top of our dummy cake -- and it looked beautiful as onlookers watched and Griffin videotaped a portion. Unfortunately, we were unable to setup the limit switches properly as I would have liked to do so. Though, the positioning system of our polar-coordinate-based rotating platform worked so well that it did not matter as much as I was worried it would. Cassie and Emily then walked in with our final, pre-frosted chocolate cake for the demonstration. While they went on to watch others demonstration, I decided to create and edit a short promo/trailer video of our Cakebot to add into the presentation that would happen in 15 minutes. ...

Demo Day is Thursday, December 18 -- but our project website  was due  Monday, December 15. Having met several times over the last week and half, my team has been pushing to finally finish our full mechanism. Griffin and I were lucky to have the electronics systems finished, except for the limiting switches, a few days ago. I tested the motors and Arduino code to ensure that we were able to move them appropriately, and Griffin worked diligently to wrap up the GUI as I tried to offer what little python I remembered. However, in the midst of finals week at both Olin and Wellesley, the mechanical aspects fell a  little behind as my teammates were fighting for space in the woodshop and laser cutter with the many other Olin students who needed it for their own projects. With the majority of my project finished, I took charge over the website as the only individual familiar with Weebly hosting-site. Originally, Griffin setup an HTML template for us all to edit but, as it ...

After the DRII, we took our compliments and criticism to heart and set off to finish what we said we would do before the final Demo Day. Griffin and I looked into the malfunctioning rotating platform and realized the issue was more mechanical than anything electrical or software: Cassie and Emily made note to handle the issue in our final prototype. Griffin and I worked heavily on integrating the pyserial code with the Arduino system: he came up with the genius idea of having the pyserial/GUI send three-letter codes that correspond with motor actions, i.e. calibration of the platform stepper, forward movement of the top stepper, extruding of the top DC, extruding of the side DC motor. We were able to record all our changes of the final sprint code using  GitHub  -- a cloud management system for sharing and collaborating on code. Griffin introduced me to the system and I plan on using it much more often now that I understand its magic. Furthermore, in testing all the m...

This design review went very well for CAKEBOT. We took the feedback from our last review and tried to apply the criticisms and encouragement we received to this sprint. We were able to demonstrate a proper integration of the electronics, software and mechanics. Griffin updated the GUI for more tip changes, "Confirmation" dialogue boxes, and on-screen drawing. While he was out at You-Do-It, he brought me 2 limit switches for calibration and I also requested some safety switches, i.e. a master on-off switch and a confirmation (or "pause") button -- all to be mounted afterwards. Below is the presentation with updated goals and videos of the demonstration. (The form is now closed but we received great feedback).

Leading up to the second Design Review, CakeBot team attacked our project with a vengeance, ordering supplies for the frosting dispenser asap and building the frame for it, searching for new motors and drivers to build the actuators for nozzle and platform movement. Cassie and Emily, once the orders came in, worked on modifying the Wilton Decorator Pro to attach to a DC motor for up-and-down movement, i.e. pressure on the frosting container. Another stepper motor, compatible with the Adafruit Motorshield, was ordered and integrated by using a belt to move the nozzle/dispenser across the radius of the cake. Griffin and I also ordered a separate stepper driver from Pololu  to drive the Rotating Platform's "high-current" stepper motor. In testing our apparatus, with a finally-mounted Decorator Pro, we were able to observe three mechanisms: Extruding the frosting to create a border: The DC motor moves the plunger downwards at a constant rate while the platform rot...

After 2 sprints -- two week periods of building and planning -- teams are expected to present in front of the class and professors for questions and feedback. Our team were persistent in our design and build despite delivery delays, system failures and more so. Unfortunately, because the parts did not come in enough time, the mechanical system could not be built. However, Griffin and I were able to pull together a rotating platform with a pseudo-calibration switch as well as a basic GUI (graphical user interface) to choose different tip sizes and frosting patterns. Cassie was also able to laser-cut a wooden cube, where we could store all electronics, for the base of the entire mechanism. See the PowerPoint presentation that the CakeBot team delivered to the class and how we hope to attain the Final Goal in the next sprint/design period. (The feedback form is closed now.) The responses we received were encouraging but critical as we are a little behind schedule. Additional...

 After our insightful meeting on Sunday, the CAKEBOT team dived into some hard science. Specifically, Griffin and I (the Sensors/Software sub-team) looked into having the platform rotate -- rather than trying to rotate the platform by hand or change the position of the frosting nozzle. To do so, we looked into using a stepper motor (360-deg versus a 120-deg Servo motor) and using the Adafruit Arduino Motorshield from a previous lab. Coding-wise, I used the sample Adafruit code to test out the four types of motor-turns : single coil, double coil, interleave, and microstep.  Double coil allows for greater torque while microstep allows for smooth, continuous turns or "steps." Interleave alternates between single and double coil for stepping. The code worked beautifully, but we painfully discovered that the motor we were using was drawing more current than the Adafruit Motorshield could supply, causing quite a bit of smoking on the chips. We sought the advice of Siddhartan and ...

At our team meeting on Sunday after the first spring review, the crew decided to become familiar with the field at hand. We baked and decorated a 9-inch cake for observation. Baking the cake did take a portion of time and for the majority of that time, the team discussed ways in which we could extrude frosting. Emily and Cassie had taken a field trip to a Baking Store and found a Wilton Decorator Pro, which consisted of a plunging mechanism to extrude frosting from the attached storage container. Additionally, the tool allowed for interchangeable tips to create circles, stars, and waves. We took such a luxury into account for our design too. We reversed-engineered the Decorator Pro to understand how we could ensure that the frosting was forced out at a constant pressure. The Mechanics sub-team (Cassie and Emily) discussed how to remove the springs in order to directly integrate the equipment into the CAKEBOT, attaching the plunging arm to a motor for vertical movement. By then, the...

At the end of every two weeks, there is a "sprint review" where professors circulate between groups to hear about and give feedback on the progress of each team project. The CAKEBOT team met for a long session the night before to finalize the physical, first iteration of the CakeBot design. We also sketched out the integration of the components for future sprints  to demonstrate that we at least thought about the mechanical, electronic and software pieces. The actual prototype itself focused on the cake rotating platform -- which we knew we would absolutely need for decorations on the side/walls of a cake -- and initial ideas on the icing dispensing system for the face. For the rotating platform, I used a cut-out circle of 9-inch diameter (for standard cake size) and we connected it to a servo motor. I then programmed the Arduino to "sweep" the servo to and fro; the motor itself was pushed into a hole cut out in the foam base. The foam base most likely will be a w...

Director Raji Patel, who also invited me to speak at the Regional Meeting, also asked me to speak at the 2014 Massachusetts STEM Summit during the MASGC breakout session with NASA astronaut and icon Sunita Williams. The talk presented a bit of a challenged as I was asked to condense the presentation of my research on "A Multiplexed Digitizer for Dark Matter Detection" to a holistic, non-technical presentation. I had to re-route the order of my presentation and focus on the "big picture" to my audience. I emphasized my own personal development during the summer, explained major decisions on the overall design of the readout circuit, and featured the importance of such research in the physics and current news arena. (See below.) I was ecstatic to be there alongside Sunita Williams and another student presenting her work. As big of an icon she is, Williams was very cordial and eager to share her experience leading up to her record for "longest single space fli...

When Professor Battat asked if I would be willing to present for the Massachusetts Space Grant Consortium, there was no hesitation in my reply. I could barely contain my excitement as he replied to the director about my response. Not only was the director Raji Patel asking me to present at their regional meeting but also the MA Stem Summit the following week. In just a two-week time period, I would be in the presence of NASA officials, state consortia directors, the Massachusetts Governor, the MA STEM Council (headed by Congressman Kennedy) and other key stakeholders. As excited as I was, I was also nervous about these events: I knew I had to nail it. This morning, at the regional meeting at MIT -- with less than 4 hours of sleep -- I gave the presentation to floor a nation.... maybe that's a hyperbole but my presentation was no less wonderful. My mother -- my greatest supporter and critic -- flew in for this presentation and Wellesley's Family Weekend to place one more laye...

WeLab/WES ( Wellesley Engineering Society ) has gotten off to a great start with almost 100 students and counting . I really want to see the engineering department grow and getting students involved in the seminars, workshops, etc will hopefully retain all those bright-eyed first years interested in engineering. Lookout, World! Wellesley students are ready to show what it means to be An Engineer in Liberal Arts and it's time for people to know about the impact of that tie. As John Maeda says,  STEM + ART = STEAM. Take a look at all the steam these students are building and what's ahead for We-Lab: Can't view infographic? infogr.am/whos-with-me-5283

Using the CoolTerm program to read Arduino serial values to a txt file, we print the serial output values of position, target position, error, and motor output and then used MATLAB to plot these values.We used the PID equation, output = Kp*Error + Ki*Total + Kd*Difference , where Error = target ­ count,  Total = total + error, and Difference = Error_previous - Error_current. With a little experimentation, we found that our control works best when Kp = 14, Ki = .01, and Kd = .1. Yet, we noticed that the accuracy of our plots was not as high as it could be with a 36­resolution encoder, which caused large steps in our plots, as seen in Figures 4 and 5. We tried increasing the accuracy by using different encoders, up to 72­resolution. Challenges: A key challenge in this lab was understanding the dynamics of PID control system and how to translate them into the encoder­motor system we built. Another challenge we had to overcome was dissecting th...

Objectives Use an analog IR reflective sensor to measure the angular position of a motor shaft. Create a closed-loop controller for a brushed DC motor with your DIY shaft encoder. Characterize and visualize the performance of your closed-loop motor controller. In this lab, we used an analog infrared reflective sensor to build an encoder to measure the position of the shaft of a DC motor. With the sensor, the more IR light that is reflected back to the phototransistor, the closer Vout will be to zero (see schematic). We used the position reported by the encoder as a signal around which to design a feedback loop that ensures your motor will go to any position you command it to (even under load). After setting up the sensor circuit with the Arduino, we began to build the encoder. An encoder is a circle with distinct patterns of black and white shapes, usually triangles, that signify on-off or high-low. We placed our 36-resolution*, carboard encoder right on the shaft...

Hello again!  It has been a while since my last descriptive post about my engineering journey though a lot has happened over the past few weeks, from PoE to We-Lab to W.E.S. to research talks. I almost have no time to blog -- almost no time ... So, to get back on track with my documenting the experience, I am submitting a series of posts about all the new developments. Olin's Principles of Engineering (PoE) PoE has kept me extremely busy as the labs have become more and more challenging, moving from simple LED lights to a 3D scanner to Proportional-Integral-Derivative (PID) motor control. PoE is meant to give students a balanced background in both electronics, mechanics and programming -- in preparation for the final project. For the final project, students were allowed to form their own teams and project ideas, which created a frenzy throughout the classroom. People heckled and raced to find a spot on highly-coveted ideas or urge others to join them in an idea with littl...

In this lab, we embarked on the journey of creating a 3D­scanner utilizing two Hobbying servo motors, a Sharp Infrared Distance Sensor, and an Arduino Uno. We created a connector that would allow us to secure a reliable connection between our Arduino and IR sensor. We patiently assembled the connector by crimping three JST connectors onto appropriately stripped wires to fit into a 3­pin JST connector. We tested the functionality of the primary parts: the sensor, the Arduino, and the servos. We adjusted and ran the AnalogInput example from the Arduino example library, which caused our sensor to blink at an increased rate whenever an object was nearby. Similarly, we ran AnalogOutSerial from the Arduino library, which allowed us to verify that values were being transmitted and that they consistently changed when an object was nearby. Lastly, we made sure our servos worked and could be controlled, using the "Sweep” example to rotate the servos. After confirming the functionality o...

Since Prof. Banzaert has been away on maternity leave, I've been working a lot on expanding the presence of the Wellesley Engineering Laboratory and knowledge of the engineering options at Wellesley. I met two other students -- one of who was in my EXTD160 class last Spring (Sam Chin) and the other being a current certificate student (Elena Shaw) -- who are interested in expanding the engineering community here at Wellesley also. With the guidance of Dean Stephan, one of the few members of the engineering steering team, I am pushing forward on my many ideas -- especially the development of a organization for students' interested in engineering for  various levels and fields . This society will engage in field trips to seminars to outreach to conferences to workshops and professional development -- all in the good name of engineering! We have much more interest in the society than I expected and I cannot wait to get things started. My list of seminar topics and field trips i...

Second day of Lab 2 and the lab deadline has been extended to the next class period! Plenty of time to work out the kinks and whatnot of the project... Though, this is a step up from Lab 1. Following from last post's updates, we have sent the pan-tilt design to the Wellesley machinist (Larry Knowles) for his advice on what materials to use and how to construct it. Hopefully, he'll be available next week and we can finish it on Monday. Furthermore, I've use the resources I found to begin writing the code for both the infrared sensor, calibration of the sensor values and MATLAB translation (visualization). The YouTube video below is an in-depth tutorial of how to use a infrared sensor and real-time draw its data into a MATLAB axis. The connector for the sensor has been developed and, when the pan-tilt mechanism and the foam object is constructed, we can begin testing the code. I am eager to see how these servo motors work. I feel that I'll be seeing more of them in ...

We're Making a 3D Scanner! I don't know how we jumped from flashing LEDs to this project, but I have managed to be both excited and scared. Lab 2 requires us to rely quite a bit on our mechanics knowledge to design and build a pan-tilt project with two servo motors and an infrared sensor. Together, the mechanical object will collect dimensions of a foam-based letter and, then, use MATLAB to draw the 3D representation of the object. I have never worked with servo motors before but I have worked with MATLAB and sensor data. Again, with my partner Ashley, we will ensure that we do not fall behind on this project like the last one. (Plus, I am eager to see what I can do!) We already have a few ideas to pursue as well as a few concerns. Pan-tilt projects are relatively simple to design but building them is another story. I am not a MechE (mechanical engineer) and neither is my partner. However, we are both trained in the machine shop and can use our Wellesley resources to ...

After we resolved the minuscule problems affecting our progress on the lab, Ashley and I worked diligently to catch up and even worked over the weekend for a long period to complete both parts of the code. Part I: Four Modes with a Single Button We had designed the operations of the four modes to be switched between but we were still figuring out the "switching" mechanism on the Saturday before the due date. Many of the examples we had seen were too elaborate and we wanted a simple solution. We found one by using millis() , a pushCounter and debounce operations. Millis() is a way to keep track of time, without stopping the entire program (i.e. delay), and we can use it for comparisons between the current timespan and a set interval to form different flashstates. On the other hand, a "button state change detection" tutorial showed us how to count presses of a button and cycle through four states. However, many times the Arduino will read several button presses ...