Gas station without pumps

2013 January 4

Parts and tools packaged today

Filed under: Circuits course — gasstationwithoutpumps @ 20:44
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The breadboards finally came, so I was able to pack all the parts and tools into 2-gallon Ziploc bags—all except the LM2903 comparators that I just ordered today and the hysteresis lab PC boards, which I still have to cut apart on the board shears at work.  The parts come to $65.50 a student, rather than the $65 I told the students about earlier, because of the addition of the comparator, and because I included 10 EKG electrodes rather than 9 in each kit (they come in sheets of 10, so dividing them into 9 per student would have been tough).

My son and I bicycled up to campus today so that he could check the installation of the drivers and software on all 12 of the computers in the lab, and install the latest version of the data logger code.  He found a bug that is due to a limitation of Tkinter names for items on a selection list—they don’t like backslashes in the names.  He had been using the names of the USB ports as names for selections, but on Windows, the port names have backslashes in them. He did a quick patch so that he could finish the installation, but he’ll try for a cleaner fix this weekend (using a separate dict to map Tkinter names to port names). I want to start the class on Monday with a demo of the blinky EKG feeding my heartbeat to the Arduino for display to the class, to give them an idea of what they should be able to accomplish by the end of the quarter.  I’ll have to see whether I can get all the components working together this weekend, so that I have them ready for class on Monday.

I’m still panicking a bit about class starting on Monday:  I’ve only gotten the first three labs written up, and I still haven’t nailed down the FET and phototransistor lab.  I may even want to rearrange some of the labs (moving the hysteresis lab earlier in the quarter, for example).

All the computers seem to be working with the datalogger software with Duemilanove, Uno, and Leonardo Arduino boards, so I think we’re ready for Thursday’s lab.

My co-instructor loaned me one of the boards he designed for EE103L, the lab connected with the Signals and Systems course.  The board consists of a clock generator (using an LM555 with jumperable capacitors and a 1-turn trimpot and a couple of D flip-flops), an 8-bit analog-to-digital converter and an 8-bit digital-to-analog converter.  The idea is to hook up a signal generator to the input, and look at the output on the scope.  Artifacts of discretization in time and voltage should be visible, and aliasing can be observed as the input frequency is increased or the sampling frequency decreased. The board has a space on it for wiring up 4th-order Butterworth low-pass filter, but that is not done on the board he loaned me, nor is it needed for the lab that the EE103 students do.

He did one thing on the board that  makes it a little hard for me to play with at home: he did some initial signal conditioning using op amps with a dual-rail supply, so he expects two power supplies externally (which he regulates to ±5v on the board). Because he has the linear regulators, I don’t have to worry about providing matching supplies, but I need about 8v, as there is a 1.7v dropout from the regulator and a diode drop from a protection diode he added, so I’ll need at least 7.5, and preferably 8v.  I have a big 12v battery (which I often use to drive my 6.6v regulated supply), and I can use a wall wart for the other supply, so I should be able to fake the power setup at home.

He also expects the signal generator to be properly centered at GND, so I’ll have to add a DC-blocking capacitor and resistor to my non-centered function generator.  Using the Bitscope function generator would be a bad idea, because it is already discretized (though in finer steps than the 8-bits of this board).

The lab itself is a bit hokey: the students are to use just the frequency of the input sine wave (which they can adjust) and the observations of the discretized signal on the scope to determine the sampling frequency.  This looks to me more like a 20-minute or half-hour lab than one that will fill the full 3-hour lab slot, so I’ll have to think of more things for the students to do—perhaps using the sampling on the Arduino in addition to the board.



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