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What I Learned in College

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Conner McCloud

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So I'm down to my last week. Interestingly, I discovered this site early in my first semester [I lurked for several months before registering]. So if you've been paying close attention, you could probably trace how my beliefs and opinions have been changed by the college experience by running through my profile.

But that's not why we're here. We're hear so you can be imparted with some words of wisdom by myself, the smartest man you are likely to come across on the internet in the next couple of minutes.


  1. Unplug things. I can't stress this enough. Being connected to a power supply fucks everything up. For one thing, you can't measure resistance if your circuit is hot. They don't tell you this in intro to circuits, but its true. Also, cutting live wire can be quite dangerous. My eye has never been the same. A more subtle issue is that PC power supplies have power and ground shorted for some reason when the thing is off. So if you're using one for your power, having it connected to your circuit will cause some false positives when doing connectivity tests.

  2. Plug things back in. I can't stress this enough. Not being connected to a power supply fucks everything up. For one thing, you can't measure voltage if your circuit is cold. This is mostly an issue when you're not expecting to see voltage anyhow - ie, you want 0 V, and when you check the voltage you get 0 V, so you assume everything is AOK.

  3. Related to the above: PC power supplies make for great cheap constant voltage sources. They might not be as accurate as a more expensive solution, but I've never found that to be a problem. They can supply massive amounts of current, and should have internal circuitry to protect itself from faults. At least, all the one's I've used have killed themselves rather than be damaged by current spikes. All I had to do was power down and then power back up, and everything was fine.

  4. Get lots of wire, with different colors. A good color scheme can mean the difference between a successful test and a failed one. At the very very least, have a color just for ground. This gives you a quick and dirty way of verifying that you don't have any shorts to ground before following the advice given in (2).

  5. Plan out your layouts in advance. This is one place where nodal analysis comes in handy. If A, B, and C are all attached to a common node, then don't connect A to B and then B to C. Instead, connect all three to some fourth point, and give them all the same color. This makes later bug checking easier, because you've got fewer pointless jumpers lying around just waiting to come unplugged or be forgotten. Instead, each pin has exactly one wire, and you can tell at a glance that A and C are connected without wasting time going through B.

  6. Larger gauge wire is actually smaller. I am forced to assume this is one of two things: a clever reference to the fact that the internal resistivity is larger, or a stupid throwback to the early days of wire sizing. My gut says the latter, but either way 0 is considerably bigger than 30.

  7. Know Ohm's law. Apply it whenever you are about to put a resistor in a circuit. Why is this resistor there? What currents will it be seeing? How much voltage can be dropped across it without causing a problem? And so forth. Some times, like with pull up/down resistors, it doesn't really matter. But sometimes it does. A back of the napkin analysis is sufficient to validate that you aren't doing anything terribly stupid.

  8. Solder is nobody's friend. If solder were an ice cream flavor, it would be pralines and dick. Avoid it whenever possible. Prefer bread boards to just running wires. Prefer wire wrapping to soldering wire. Prefer through hole to surface mount. For prototyping, its just faster. I like to think of soldering as premature optimization. I'm not even sure this circuit is going to function, do I really care that my contacts are 100% solid? Probably not. Obviously, sometimes you know that you need to keep noise to an absolute minimum, or heat requirements require surface mount, or whatever. In those cases you should adjust accordingly.

  9. On your standard Radio Shack wire strippers, that screw allows you to change the size of wire you are stripping. Closer to the cutters allows for thicker wire, closer to the handle allows for thinner wire. Now that you know that, you can stop accidentally cutting your wire because the stripper is expecting a higher gauge.

  10. Many places will give you free samples. Take advantage of this. Microchip and Freescale are both pretty generous.

  11. LabView is very nice. The hardware can be pricey, but I've grown to like it for any sort of transient analysis. It's not quite good enough to replace an oscilloscope for fast circuits, but if you're just calibrating an accellerometer or figuring out how a circuit behaves then it's more than adequate. Plus, graphical langages are just going to get more important in the coming years, so it'll probably be useful to be familiar with some now.

  12. Prefer a pre-built solution to doing it yourself. This is a lot like programming - the STL is right there, why are you designing your own linked list? If you need USB support, just buy a PIC with USB support. Maybe it'll be more expensive, but you've saved yourself the hassle of implementing the interface yourself. Plus, see (10). This applies to more than just high level communications - many common applications have IC solutions available if you look for them.

  13. Understand how capacitors and inductors behave under steady state conditions. Their pictures spell it out - a capacitor has a giant gap between its terminals, so in steady state it is an open circuit. An inductor is a solid line, so in steady state it is a short. This also gives a hint as to their transient behavior. Inductors allow current to flow, so they fight current changes [V = L dI/dt], whereas capacitors have a voltage difference, so they try to maintain a constant voltage [I = C dV/dt].

  14. Always always always double check your resistance values before you insert them into a circuit. This is a thirty second test, and can save you some agrivation when you realize that you transposed two colors and ended up with a resistor a factor of ten smaller than you wanted.


That's all I can come up with. You have officially learned as much as I have in the last five years. Congratulations, and take that fancy diploma.

CM
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Nice post... many of things I have done on multiple occasions [smile]

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