Blood pressure lab part 2

I spent long hours in the lab yesterday (10 a.m.–6:30 p.m.), because students were not as far along as I had thought by the end of Tuesday. I stay in the lab until all the students are finished, even if that is a couple of hours past when the lab should end. A lot of students were still debugging their breadboarded instrumentation-amp circuits 2 hours into the lab session, when I had thought that they would be soldering after at most an hour more breadboarding.

Debugging on both the breadboards and the soldered boards took a lot of time, but the problems were pretty much the standard ones:

• power not connected
• wire missing
• wire to wrong location
• power supply hooked up backwards to one of the chips
• bent pin on chip not making contact with breadboard

A couple of groups asked me for debugging help but did not have a drawn schematic to work from.  As I had said earlier in the quarter, I would not help them debug unless they had a schematic to work from.  (I think in both cases the problem was that they had connected up one wire incorrectly, but without a correct schematic to work from, there was no way that they could detect the error.)  Some students have been a bit sloppy about trying to work out of their heads rather than putting things down on paper, and this sloppiness is beginning to be a problem for them.  It has mainly been the weaker students who have been being this sloppy, so perhaps it has been more the case that they have been trying to work out of other people’s heads—copying bits and pieces from other students rather than working things out themselves and then implementing it.

I won’t be helping students debug unless they have shown some effort at making their designs debuggable (like having a clean schematic before they wire things up).

I’m not 100% sure, but I think that all but one group got a soldered instrumentation amplifier working and a blood-pressure measurement run done with it.  The one group that didn’t get that far did have a breadboarded amplifier working.

There were some students missing due to illness, so I’ll probably have to arrange some time next week for make-up lab times.  I’m not sure when that can be.