(Last Update: 2014 March 5 21:29 PST )
This "group tutorial" is a prototype run for a new course, which we are hoping to number BME 88A: BMES Freshman Design Seminar.
The current goal for the design projects is to have small teams (2–4 students) design low-cost lab equipment suitable for hobbyists or home school, middle school, or high school science labs. Think of it as "science on a shoestring" or "thrift-store science". We'll be trying to duplicate the functionality of expensive science teaching tools (such as those sold by Pasco and Vernier) at a fraction of the price.
A major goal of the course is to get students thinking like engineers: asking questions like "How can we make something that does this?", "What are the constraints on the design?", "Will this part do what we want?", "How much would it cost to do that?"
Please feel free to leave comments on the blog with suggestions for the course.
I've collected student responses and started adding comments. Go look at what fellow students have found—there's some cool stuff there!
For the photodiode and the phototransistor, report the dark current, the voltage drop across the device (that would be collector-emitter saturation voltage for a phototransistor and the open-circuit voltage for a photodiode), and the sensitivity (current at 1mW/cm2 at λ=940nm, which is the wavelength where silicon photodiodes and phototransistors are most sensitive).
Find a plot of the spectral sensitivity of a silicon photodiode or phototransistor (it need not be from the data sheets you found—all the silicon photodiodes and phototransistors have similar properties, unless the packaging they are in filters the light).
We want to make a circuit so that the full-scale (5v) reading on the Arduino corresponds to an irradiance of 204.8μW/cm2 at 940nm, so that each of the 1024 steps corresponds to an increment of 0.2μW/cm2. Remember that 1000μW=1mW. (We may not be able to use the full range, as the circuit should saturate at a somewhat lower value, depending on the saturation voltage or open-circuit voltage of the photodetector.)
Update 2014 Feb 6: Q1 is intended to be an NPN phototransistor, not PNP as shown here!
For the circuits above, figure out what values of R1 and R2 to use to get the desired voltage range at A1 or A2. Look up what standard resistance values are available with 2% tolerance, and pick the nearest one. (Hint: Google is your friend for finding tables of information.)
In class on Monday, we'll try building this circuit and seeing how it works with the Arduino Data Logger.
Also for Wed, read the Wikipedia article on optical dispersion.
I recommend using Digi-key's search feature (looking for RGB LED) to see what parameters are usually most important to designers. I recommend using Digi-key's free web tool SchemeIt for drawing a circuit diagram. They don't have an RGB LED symbol, but you can make one out of 3 LED symbols (I'd use variant 1 for that).
Bonus: find an RGB LED that is common-anode, and do the same design exercise with it. (If Digi-Key's search doesn't turn up a part, try using Google.)
8:HIGH 9: LOW 10: LOW 8: LOW 9:HIGH 10: LOW 8: LOW 9:HIGH 10: LOW 8: LOW 9: LOW 10: LOW
As a matter of common programming style, there should be a "block comment" at the beginning of every program telling what the program does (from a user's standpoint, not how it works from a programmer's standpoint), who wrote it, and when it was written. You may work on the programs in pairs (not larger groups), but the names of everyone who worked on the program should be provided in the comments at the beginning of the program.
Turn in a printout of your program. This program is simple enough that I don't need evidence of it working—for other class you may be asked to turn in the source code electronically, so that the graders can test the program, or provide input-output pairs that show evidence that the program is working correctly.
For those who find this program too easy, you can challenge yourself to do more ambitious programs:
Date | Lecture Topic(s) | Due |
---|---|---|
Mon 2014 Jan 6 | administriva. First day of freshman design seminar discusses skills students bring to the class, based on the intake survey. | |
Wed 2014 Jan 8 | design exercise: trying to specify what a spectrophotometer needs to do (to be continued). Second day of freshman design seminar discusses the design exercise I tried using a spectrometer as an example. About all I managed to convey was that design is hard if you don't know enough about what you're designing. Perhaps I should try an example next year that more students are familiar with—I thought that this would be a familiar concept (unlike, say, a polarimeter). I was wrong. | |
Mon 2014 Jan 13 | lab tours(Baskin). Third day of freshman design seminar covers the creation on an e-mail discussion list for the class and lab tours | |
Wed 2014 Jan 15 | design exercise: photospectrometer continued. Fourth day of freshman design seminar discusses the continuation of the spectrophotometer design exercise. | |
Mon 2014 Jan 20 | MLK day, no class | |
Wed 2014 Jan 22 | photosensors (emphasis on phototransistor). Fifth day of freshman design seminar was spent looking in more detail at one part of the photospectrometer—the photodetector. | |
Mon 2014 Jan 27 | feedback on homework, data sheets, resistor choice for phototransistor. Sixth day of freshman design seminar discusses the feedback on the first homework and reading a phototransistor data sheet. Algebra and calculator skills were even lower than I expected. | |
Wed 2014 Jan 29 | lab tours (Biomed). Biomed lab tours and online discussions discusses the 7th day of class (lab tours) and the difficulty of getting an online discussion going. | |
Mon 2014 Feb 3 | Photodiodes and LEDs. Seventh day of freshman design seminar (actually 8th) discusses photodiodes and LEDs, along with feedback on the photodiode homework. | |
Wed 2014 Feb 5 | Karplus ill—discussion of possible projects lead by Sean Hacking | |
Mon 2014 Feb 10 | discussion of calorimeter and LED homework, intro to Arduino programming. Ninth day of freshman design seminar (actually 10th) discusses return of two homeworks (colorimeter design and LED resistor sizing) and the first lesson on Arduino programming. | |
Wed 2014 Feb 12 | Intro to control and temperature sensing (bimetal strip and thermistor). Tenth day of freshman design seminar (actually 11th) discussed thermal control and thermistors. | |
Mon 2014 Feb 17 | President's Day, no class | |
Wed 2014 Feb 19 | Twelfth day of freshman design seminar (back to correct numbering) discussed first Arduino homework. | |
Mon 2014 Feb 24 | Thirteenth day of freshman design seminar briefly discusses the drafts of the design reports and teaching programming of simple control methods for temperature control. | |
Wed 2014 Feb 26 | Fourteenth day of freshman design seminar discusses breaking into the design groups and answering questions from each group separately. | |
Mon 2014 Mar 3 | Fifteenth day of freshman design seminar discusses a looming TA strike, group advising, and t-shirt design. | |
Wed 2014 Mar 5 | Sixteenth day: Arduino demo discusses an Aruino demo that included relays, nFET control of a motor (including PWM), and using a pressure sensor to control the motor. | |
Mon 2014 Mar 10 | ||
Wed 2014 Mar 12 | ||
Mon 2014 Mar 17 | ||
Thurs 2014 Mar 20 4–7 p.m. | Final exam slot | Reports and demos. |
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