Gas station without pumps

2015 March 31

First lab for Spring

Filed under: Circuits course — gasstationwithoutpumps @ 21:50
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I had a very long day today (as I expect all Tuesdays and Thursdays to be this quarter).  It started out with me in a panic, because I had gotten a message late yesterday afternoon, telling me that the parts kits for the course were not ready yet, but not telling me what was available, so I didn’t know whether I’d be able to run today’s lab or not. I thought I probably would be able to do the essential parts, because the main part of the lab was soldering headers onto the KL25Z boards, and the boards and headers were ordered from Digi-key, which has very fast delivery (thanks to their almost instant packing of parts for shipping and their using the post office rather than FedEx, which has been unbelievably slow this year).

I went into work a bit early this morning to check on what parts were available (after a night of thinking about what labs I could do if the KL25Z boards were not available—pretty much only the thermistor lab scheduled for next Tuesday, and that takes about an hour of setup to prepare the lab and have hot water and ice water available).  As it turns out, the person who had informed me of the incomplete parts list had sent out a spread sheet with the information—he’d just forgotten to CC me on it. The KL25Z boards, the headers, and the USB cables were all available, so we could do the main part of the lab.  We couldn’t do the unpacking of the parts kit and identifying parts, but that can happen later, as the parts come in.

For Thursday’s lab, it would be good if they had their breadboards, resistor kits, and electrolytic capacitors—but I don’t know whether those will all be ready by then (the resistor kits haven’t all arrived yet).

Once the boards arrived, I started part of the class soldering (we only had 6 soldering stations, two of which were not very functional, despite my request 2 years ago for enough soldering irons for the 12 benches).  While some were soldering, the rest were downloading the PteroDAQ software and trying to get it to work on their machines.

The soldering went well, with one serious exception.  One student soldered in the connectors on the wrong side of the board, and neither the group tutor nor I noticed in time (and we could have, because we had looked at the board and just not noticed). We helped remove the connectors (removing a 2×10 female header from a board is a lot of work), but the student did not have enough time to get all the connectors replaced by the end of lab.  The tutor will provide some supervision at another time before Thursday’s lab to finish up.  All the solder joints looked clean—I saw neither bridges nor voids.  I did send several students back (more than once) to reheat cold-solder joints, but in the end all the students had good connections.  Since only 2 or 3 of the 32 students had ever held a soldering iron before, I think that getting each to make 64 good solder connections is a pretty positive outcome.  They’ll have 3 more labs this quarter where they will have to solder (their own designs, not just headers), but I think that they’ll approach those labs with more confidence now.

The PteroDAQ downloads were not quite as successful.  I think that everyone managed to get the MBED.ORG download software installed, and transferred the daq_kl25z.bin executables to the KL25Z boards. Most (all?) got PteroDAQ working with the lab computers. But few, it any got PteroDAQ working on their own machines.  There were three classes of problems:

  • On Windows 7 machines, I forgot how to use the mbed-usb-windows.inf files to install Windows drivers for the USB port on the KL25Z board. I looked it up after class before going home and found a page about installing Windows drivers for Arduino boards that seems to have all the right instructions (but use the .inf file in the PteroDAQ extras directory, not arduino.inf): http://arduino.cc/en/guide/windows#toc4
  • On Windows 8 machines, I don’t know whether the same approach will work, but I hope that some of the students will try. The approach given in the MBED handbook did not seem to work, but I’m not very comfortable with Windows, so I may have missed something obvious to a serious Windows user.
  • On Mac OX 10 machines, we had two problems:
    1. OS 10.10, 10.10.1, and 10.10.2 were not willing to write to the MBED device. This seems to be a known problem that the MBED user community is pretty upset about. The MBED developers have been working (slowly) on the bug since last October, with patches for only a few of their many supported boards (not, so far as I can see, the KL25Z).  There are claims on the developer forum about the bug that OS X 10.10.3 beta finally fixes the bug, but no one in their right mind would suggest that students install Apple beta code on a machine that they plan to use for anything. A student was going to enter an “issue” ticket on the PteroDAQ website, but it doesn’t seem to be there yet.
    2. If the Windows 7 machines in the lab were used to put the daq_kl25z.bin onto the boards, then OS 10.10 seemed to work ok (a student got it running), but OS 10.10.1 and 10.10.2 machines failed.  The problem seemed to be with Tkinter: the selection of the port for the KL25Z was not sticky—it deselected itself within a second of being selected. Some of the students had freshly downloaded versions of Python 3.4, so the problem doesn’t seem to be with old code, though I suppose a Tcl/Tk incompatibility with Python is possible—I didn’t have any of the students try re-installing Tcl.  I hope that a student with an OS 10.10.1 or 10.10.2 machine will post an issue ticket about this issue on the PteroDAQ website also.

    I’m now very glad that I did not “upgrade” my old OS 10.6.8 Mac to 10.10 on my 2009 MacBook Pro—it seems that I would have broken many of the things that I rely on my Mac for. Perhaps I’ll wait until I get new a new laptop before “upgrading”—and I won’t buy a new Apple as long as they don’t work with MBED, even though my current laptop has a very sick battery and is beginning to show its age. (I have no intention of buying a MacBook with only one USB-C port, either: I routinely use the power cable, the ethernet port, the firewire port, the display port, both USB ports, and the SD card port, and often use three or four of these at once.)

It would be really nice to have installation instructions with PteroDAQ—I forgot some steps of how to do the installation on Windows (the driver installation), and it would be nice to have a written description of the steps for a Mac that I could just point students to, rather than walking them through it.

I set up a mailing list for the class this evening, and I hope that students who manage to get PteroDAQ working on Windows 8 or OS 10.10.1 or 10.10.2 will share the information.

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