I am not afraid of ridicule, this is a fact. But sometimes, ridicule is too much even for the best of us.
When I was in college, as many EE bachelors had (at least in my time), we had a digital design basics class, we would do these gigantic protoboard circuits with ANDs, ORs, etc., etc. and then the teacher would come and check them. Final project was the same thing, only bigger (don’t remember what it was, it might have been an ALU or something like that). So I did my project, my Karnaugh maps (anyone actually uses these still?) and everything worked out fine.
Then the teacher came. I gave him my report, he looked at it, asked me a couple of questions and finally asked me for the logic probe to start checking. He moved some DIP switches around, and started reading the output: 0,0,0,0,0…I was shocked, I cursed Murphy’s Law once again and blurted out something like: “But I…it was worki…really!”
Teacher looked up the table, then up to me, grinned and said: “you know what? It works better if you turn it on”. For a second I must have made a funny and confused face (which I still carry around most of the time) and then it hit me, power source was off. I was so ashamed, I thought I would get a bad grade just based on extreme stupidity, I didn’t, got a good grade and a valuable lesson.
Several years later a colleague of mine got a question from a customer asking why his circuit wasn’t working. Upon examination of the schematic and layout files it was found that the power source pins of the MCU were never connected…looks like that guy could have benefited from making the same mistake I made.