(Slightly) re-engineering the original
I used the original CBL with my students since the devices were first marketed. Over the years we endured some of the hardware weaknesses I always felt were inherent while attempting to program around others which students themselves brought to the devices. Some of these weaknesses caused some colleagues to abandon the CBL altogether but I felt the gains outweighed the losses, and because I used them for so many different things in the Honors Chemistry course (and we made what I considered a significant investment in them) I tried to patiently persevere.
In 2006 my then colleague, Chris Dartt, and I decided to make a few modifications to the CBLs which we felt would make our lives much simpler in the lab. These modifications address two major issues I had with the CBL almost since we first took one out of a box:
2. Power is supplied to devices only intermittently unless the
programming is set for continuous
The first issue had been discussed many times among the Honors Chemistry teachers. Early on we toyed with the idea of getting rid of the jack and hard-wiring a link cable into the CBL. One less connection to go bad, was our reasoning. Our experience with the early right-angle plugs, however, made us hesitate. Anyone who used those cables frequently will surely recognize the picture at the right. Not only were the right-angle plugs a bad design, there were poorly manufactured. We had too many plug tips come off inside calculators and CBLs. Thus we feared that a CBL would be out of use if this happened to the plug permanently attached to it (at least until we could replace the cable). So we did nothing and tried to keep after the solder joints.
Some of the most complicated CBL work my sophomores did was pH or conductivity titration. There is calibration to execute correctly, set-up of the collection and graphing parameters, and so on. Doing all or some of this and finding that the CBL was not paying any attention because of a bad link connection was disheartening and soon generated a chorus of voices calling the instructors name. Meanwhile other non-electronic problems were taking place (as they always do). One can only take so many days like this and at the end of one particularly grueling one I found my colleague Chris Dartt in the lab looking intently at a CBL. I knew that look, having stared in frustration at the little beasts many times myself. Fortunately there was no hammer in the near vicinity.
We had discussed CBL problems many times before and I had gradually brought him up to date on the history behind the things we had tried. As we started to talk again about the problems we were still having I casually said Well, we could just remove that jack and add a cable coming out of the case. One less connection. He agreed this was a worthy idea and added that the jacks on the calculators, although possibly just as flimsy, did not see nearly as much action as a CBL which was potentially used by five different students in a day, many times a year. We talked a little more about it and he offered to convert one of the CBLs as a test case.
In a few days we had a working model and every time a student had to make up a lab or we needed to use a CBL we grabbed that one. It behaved well and gave us a chance to consider optimum cable length for a mixture of TI-83/84 calculators. When Chris offered to do the entire class set over Spring Break I proposed to look at the power issue and see if it would be possible to eliminate one more headache in the form of the cheater cords I had designed. If I could find a simple way to solve this problem internally I would do the entire class set.
The plan was to use these altered CBLs for a year and then decide whether to similarly improve the set used by the AP students.
The weakest link
Opening up a CBL can be quite a challenge without the right tool. A very few of the 22 units we worked on had small Phillips-head screws in the back. Most had screws with little star-shaped slots that require a T10 Torx drive. My local hardware store knew exactly what I needed when I showed them. Removing the batteries first makes opening the case easier.
The entire circuit board should be removed and this is accomplished by removing the Phillips-head screw in the middle of it. Sometimes this screw holds down a postage-stamp sized circuit board that sits on top of the main board. Sometimes not. Just dont break any wires. I found a surprising amount of variation in the innards of the 22 cases I opened, so its not possible to predict what you will find. You'll have to slip the battery clips off their little posts to remove the board from the case.
Chris used a small cable tie to restrain the cable on the circuit board and hopefully prevent students from pulling it loose. He used a 7/16 drill to make hole in the side of the front half of the case (about 4 from the bottom) and then gently pulled the drill sideways to make a slot for the cable. This size slot makes the cable fit snugly and the hole is drilled fairly close to the edge so that when the case is reassembled the back presses gently on the cable as well. Its not going anywhere.
I used an Exacto knife to slice through the circuit board trace. The space is sort of tight and its difficult to see exactly when the deed is done (at least with my bifocals) so I began to use a pH amp/electrode combination with the CBL in multimeter mode. While the trace was intact there was some kind of voltage reading between 1 and 2 volts (depends on the pH of your storage solution). Once I had succeeded in severing the trace the reading became something negative or a small positive millivolt reading. I also tried using a multimeter to simply check for power at the jack but lacked sufficient hands to easily get everything where I wanted it in close quarters.
Survey says ...We used the CBLs for a full year after the alteration. The students were suitably wowed but there were still some who could not manage to insert the link plug all the way into their calculator jack (so much for the iPod generation). Short of genetic re-engineering, there is probably no solution for this problem. Still, thats just one problem and "easily" detected (cant you see that the plug is hanging out of the jack????????).
The following year, pleased with the improved stability and performance of the altered CBLs we decided to modify a second class set for the AP students. Mission accomplished.