Student "edition" found at {csi dot journalspace dot com}.

Maybe I shouldn't have started this blog now, not with everything that's been going on.

In the session of my Computer Systems Organization lab for the ninth week of the third term, their new experiment was about the flip-flops that I discussed in the previous task.

For the first flip-flops I showed them, it was easy because all they had to do was connect the gates in the same was as it was shown in the lecture, then they had to make the inputs in the same sequence as I gave them in the truth tables, to make sure that they understood certain inputs will have different outputs depending on the previous inputs and outputs.

For the next few flip-flop circuits that we had discussed, they needed to be able to construct a clock pulse circuit. This required a new chip, called (or numbered) the 555. It was half the size of the chips they are used to working with, having only eight pins instead of fourteen.

I have them a circuit to test the 555, using several resistors and a capacitor (whose charging and discharging controlled the on and off phases of the timer).

When they completed the test that had a light emitting diode lighting and shutting off several times, then I told them how they could connect the circuit to the flip-flop they were supposed to make that needed a clock pulse.

This is where they had problems, because for one thing, the two light emitting diodes that were supposed to represent the complementary outputs of the flip-flop did not show consistent results.

When one of the light emitting diodes was on, the other one was supposed to be off. But one of the diodes followed the same twinkling of the clock pulse, while the other stayed either on or off the whole time that the input or inputs was not changed. And we had not yet gotten to the part where the invalid input had been used yet.

One of the difficult parts of this experiment is that troubleshooting with non sequential circuits isn’t the same as with the previous examples of the gates, so we had to postpone it for the next meeting.

Session 1039 did not show consistent flip-flop outputs. Class dismissed.