Our most recent labs included creating a variable DC power supply, and then using it to charge a rechargeable battery. The variable DC supply turned out to be fairly troublesome for many of the groups, since it involved a lot of soldering and a lot of components. The DC supply consisted of a full wave rectifier, a handful of capacitors, a voltage regulator, and a potentiometer. A lot of students tried to compact their components tightly, but that often made for wiring headaches, especially since we were using untinned perfboard. To help out one of the teams, I rewired their board, being careful to arrange the components exactly as they were on the wiring diagram. This significantly simplified soldering job, as most of the nodes that needed to be soldered together we're all laying in a neat row. It occurred to me that simplifying the layout of the circuit elements is roughly equivalent to practicing good coding style in that you are massively reducing the likelihood of a mistake and making the overall design much easier for other people to follow. We had a nice classroom discussion about importance of good engineering practices in order to stack the odds in one's own favor for success.
|Our variable power supply with circuit elements all laid out in a row, just like in the circuit diagram.|
|The resulting solder work is fairly easy to follow. You can see the ground bus going from left to right across the bottom.|
For yesterday's lab, we used the variable supply to charge a battery. This was an interesting challenge, as students had to select both the power supply voltage and the current limiting resistor value. They had to make sure that they pick a power supply voltage that we could actually generate, a resistor value that we actually had, keep the power below what the resistor could safely dissipate, and keep the total charging time between 10 and 100 hours. That last constraint is because we were attempting to create a trickle charge. Overall the lab went well, but it was a little anti climactic, since battery voltages don't vary all that much between being charged and discharged, so there wasn't a whole lot to observe over the hour or so that we let our batteries charge up.
I'm looking forward to tomorrow and Friday, as it's back to the hospitals! Tomorrow we will return to Nandaime, and Friday we will be visiting a new facility in Managua which is run by the National Ministry of Health. Its not a hospital per se but rather a large central facility where they collect equipment from around the country to be repaired. Stay tuned for updates.