Gas station without pumps

2014 February 26

Fourteenth day of freshman design seminar

Filed under: freshman design seminar — gasstationwithoutpumps @ 21:39
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Today’s class went fairly well—I started by returning the students’ drafts of their design reports and taking general questions.  Most of the questions were about the format I was expecting for the final report (which is due 3 weeks from tomorrow).

We then broke into groups and and the group tutor and I circulated answering questions.  I had some time with each group.  With the incubator group, which had mentioned using transistors to control power to the heater, I discussed how to use nFETs and how to read some of the critical specifications.

With the centrifuge group, I talked with them about the need to keep the motor case from turning—the torque on the motor is the same as the torque on the rotor.  We also talked about how to measure the rotor speed, and the difficulty of printing large objects with a filament-style 3D printer (I suggested they look into buying a used cooking pot at the thrift store to make the case, rather than trying to 3D print it).

I only talked for a short while with PCR group, mainly about relay-based control vs. FET-based control (relays are simpler to design with, but can only do on/off control, not PWM for proportional control).

The students seemed to pretty excited about their projects, and stayed on topic for the full 70 minutes (80 minutes, actually, since we ran over by 10 minutes before anyone noticed).

Thirteenth day of freshman design seminar

Filed under: freshman design seminar — gasstationwithoutpumps @ 00:49
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I collected two of the three project report drafts on Monday (the other was turned in late, and I haven’t had a chance to pick it up yet).  The reports are looking better than the initial proposals—the groups are beginning to flesh out their initially vague ideas with some details (like calculating how much power is needed to heat the block in the PCR machine).  They have 3 weeks until their final report is due, so I expect that the drafts will continue to improve.  Of course, it is possible that the rate of improvement may be more or less than my expectations (more and their grades go up, less and their grades go down).

On Monday, we tried developing the control algorithm needed for thermal control for the incubator project and the PCR machine.  Because of the amounts of power needed, and the lack of electronics sophistication in the class, I recommended using a relay rather than transistor switches.  This limits them to on-off control, rather than proportional control or PWM control, but even developing the program for simple on-off control took us most of the hour—the idea of programming and the level of detail needed to communicate the idea to computers is still very new to them.

On Wednesday, I expect to break into groups, and the group tutor and I will visit each group trying to answer questions and help them work out the next steps in their design and try to figure out how to get some prototyping done.  Even a cardboard mockup would help them work out some of the problems.

2014 February 19

Twelfth day of freshman design seminar

Filed under: freshman design seminar — gasstationwithoutpumps @ 23:12
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My counts of which days were which in the freshman design seminar were all messed, so three of my blog posts were misnamed:

date which day of class blog post
Mon 2014 Jan 6 1 First day of freshman design seminar
Wed 2014 Jan 8 2 Second day of freshman design seminar
Mon 2014 Jan 13 3 (Baskin lab tour) Third day of freshman design seminar
Wed 2014 Jan 15 4 Fourth day of freshman design seminar
Wed 2014 Jan 22 5 Fifth day of freshman design seminar
Mon 2014 Jan 27 6 Sixth day of freshman design seminar
Wed 2014 Jan 29 7 (Biomed lab tour) Biomed lab tours and online discussions
Mon 2014 Feb 3 8* Seventh day of freshman design seminar
Wed 2014 Feb 5 9 no post (ill and group tutor ran class)
Mon 2014 Feb 10 10* Ninth day of freshman design seminar
Wed 2014 Feb 12 11* Tenth day of freshman design seminar
Wed 2014 Feb 19 12 Twelfth day of freshman design seminar (this post)

Today we started by having the students turn in their Arduino programming homework, then start writing the program as a group. I told them that I particularly wanted those who had trouble with the assignment to provide input—I’m trying to get them to realize that questions and confusion are normal, and that the right action to take in college is to ask questions, rather than to hide ignorance.

This particular assignment was expected to be hard for them—I had not done the scaffolding for it that I had originally planned, but threw them into it with very little preparation. I told them that, but also that I was trying to get them used to looking things up and figuring them out, rather than waiting to be told exactly what to do. Again, I’m trying to get them out of the “regurgitate what the teacher said” mode that K–12 education has trained them into. If I accomplish nothing else this quarter, I hope to increase their willingness to ask questions (of their teachers and of the things they read).

We did get the program written, with some digressions into the difference between “==” and “=” in C++ and the convention in C and C++ that 0 is false and any other value is true. I also managed to work in the importance of good variable names to tell people what things meant, though this particular program doesn’t need any variables.  The students now have the notions of serial execution, conditional expressions, if-statements, digital I/O, serial communication (we had a digression into baud rate), and the Arduino setup/loop structure, which may be enough for their projects—they may also need analogRead(), which I should be sure to demo on Monday.

I then typed in the program we had created together and demoed it with Arduino. I had deliberately left in a bug that I had spotted (no space between the printing of the different fields), and the class spotted it and came up with a reasonable correction when the first output came out.

We only had about 10 minutes left, so I gave them feedback on their project proposals:

  • Type homework for college classes!  Two of the groups had turned in hastily scribbled notes.
  • Give explicit specifications for the project.  How big an incubator? How precisely does the temperature need to be controlled? How fast does temperature have to change for PCR? What temperatures are needed and how precisely? How many tubes need to be run through the PCR machine at once?  How much acceleration does the centrifuge need to produce? How precisely does the speed need to be controlled?
  • Provide a block diagram giving all the components of the system (power supply, motor, fan, rotor, temperature sensor, … ) and lines showing the connections.  I talked about the importance of specifying the interfaces between components so that people could work simultaneously on different parts, and the need to renegotiate interfaces if the initial specification of them caused problems.

We talked a bit about prototyping—I want them to build something and learn enough to make an improved design, even if they don’t get a fully functional prototype.

For Monday, I assigned them the task of fleshing out the specifications for their project and producing a block diagram, filling in as many details as they could.  The group tutor is going to try to find time to meet with each group for an hour before then, to help them with flesh out their designs.

 

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