Introduction... & general waffle.
To learn practical electronics, all you have to do is follow a few golden rules. The most important being....
If you have a brain the size of a planet, and the manual dexterity of a concert pianist we can start you immediately on assembling microcircuits. (In such a case, this lab is not for you!) If, however, you seem to have the mind of a gerbil and fingers permanently tied in knots we may be able to help you...
Firstly, remember that practical electronics is a skill. (Just like being able to drink two pints of Export in fifteen seconds.) Some people seem to be born with a flair for it, but the rest of us can learn to do it given patience and practice. If you don't know already know how, you will need time to learn to solder, how to lay out circuits, how to read circuit diagrams, etc. The purpose of this course is to give you a chance to learn these things.
All of the circuits for this course should be soldered onto the boards we have provided. Do not use the “breadboard” (the slab of plastic with lots of holes) on top of the power supply. Although, at this point, you may regard this as gratuitous cruelty, this is only part of the reason. Breadboards are expensive, give poor contacts between components, and are riddled with stray inductances and capacitances which sometimes produce odd effects. Once you have learned how to do it, soldering is a quick and easy way to make dependable connections between electronic components.
When you start a lab afternoon, switch on your soldering iron, oscilloscope and signal generator. Leave them on until the end of the afternoon. This ensures that you won't have to keep wasting time waiting for them to warm up. What's more, most electronic equipment wears out faster if you keep turning it on and off, so you're helping to save money on repairs. (O.K., so our electric bill will be higher, but at least it helps keep the lab warm in the winter!)
The electronics lab works a little differently to the general Physics one. This is because the experiments are designed to be cumulative — things you discover in early experiments are needed for later ones. You should therefore stick to the following general rules:—
- Write your name on the cover of your lab script. The right-hand pages of the script give you instructions about the experiments. Use the ‘blank’ left-hand pages to record you results, write answers to the questions in the text, etc. At the end of the set of lab afternoons this script will be collected and marked. No name, no mark!
- Read the lab script. Obvious really, why do so many people ignore all these pearls of wisdom? The script gives all the basic instructions and asks some questions and even some of the answers! You will be marked for writing down correct answers to these questions in your write-up.
- When in doubt - ASK. The electronics demonstrators are there to help you. If you don't understand the lab script, or if your circuit isn't working correctly (or if you aren't even sure what “correctly” is), just ask. You don't lose any marks for asking, but you will if don't ask and end up getting the experiment wrong! If you can't see a free demonstrator you can ask another student. This is particularly useful if they seem to be getting along faster than you (doesn't everyone?). It may reveal that they are just as puzzled as you. On the other hand, they may give you some help. (Answering your questions may also slow them up a bit, and stop them from getting embarrassingly too far ahead of you!) Mind you, a demonstrator might have given you the right answer...
- Write up your report in the script. Make it clear just what you have done, what the numbers you are writing down mean, and what the answers to any questions are. There is no need for extra bits of paper stuck into the book. If you can't get it all in, you're writing too much. You don't need to re-write the printed instructions, but you do need to record enough so a marker can, six weeks later and without you there to ask, know what you did and how you got on. There are no marks for stuff we can't make sense of. Simple sketches of waveforms are particularly useful when describing what you measured. If you aren't sure what to include in your write-up, ask us!
- No pencil, no scrap paper. It is a bad habit to write ‘preliminary’ results in pencil or on scrap paper. Scraps of paper can be lost. We need to know what you did during the experiment. If you just write down something like, “The resistance I measured was 1k
”, when the correct answer is, say, 100k
we don't know what mark to give you. Was the error a slip of the calculator, or did you perform the experiment incorrectly? If you give us your raw data we can see where you went wrong and give you a mark. It also gives us some idea of how long the experiment took you and where the difficulties might be. (...and, yes, you can use pencil for graphs...)
- Write up each section BEFORE going on to the next one. The course is cumulative. You need to understand earlier sections — and have some of the results — before following sections make sense. i.e. if you don't work things out & write up as you proceed, you'll end up missing things (mostly marks!)
- Attend the lab at the correct times. This gives us a chance to see how you you are getting on. It also proves you are doing the work!
- Switch your equipment off before you leave. This is a good safety point. It also stops the batteries in voltmeters, etc, from flattening overnight.
- Always work at the same bench. This is ‘yours’ for the duration of the lab session. Although you have to ‘share’ it with some other students on other days, so please leave it as tidy as you'd want them to leave it!
Your aim should be to proceed carefully through the work described in the script. There is no need to rush through to the end. Your marks will depend more upon thoroughness and understanding than upon how far you got. Learning electronics is a step-by-step process. If you skip a step you will have difficulties later, and make mistakes which you may not notice.
A common supply of components is kept for your use. Oh, and when you get a component out of a drawer or box check that it is what the label says it is! Some people (not you, of course) put things back in the wrong place. Resistors are colour coded. The code is shown on this page. If you aren't sure how to read them (or if you are colour blind) use a DVM or Avometer to measure their values before you use them — failing that, ask a demonstrator.
Resistors are normally supplied in standards sizes and shapes. This shows itself in two ways. Firstly, their resistance values normally follow the ‘E12’ series; 1·0, 1·2, 1·5, 1·8, 2·2, 2·7, 3·3, 3·9, 4·7, 5·6, 6·8, 8·2, all multiplied by a power of ten.
So 150k
and also 2·7k
are E12 standard values, but 3·5k
isn't.
Secondly, normal resistors are able to bear power dissipations of 1/4-watt, 1/2-watt, or 1 watt. The E12 series looks peculiar at first sight, but each value is around 20% bigger than the last. This means that, when you choose the closest E12 value to the resistance you ‘really want’ you're never forced to use a resistor which is ‘wrong’ by more than about 10%.
Report any malfunctions or missing items to a demonstrator or lab technician. Yes, equipment and components do fail and need to be repaired/replaced. Don't worry, it happens to other people, too! Don't just take things from the next bench.
Content and pages maintained by: Jim Lesurf (jcgl@st-and.ac.uk)
using TechWriter and HTMLEdit on a RISCOS machine.
University of St. Andrews, St Andrews, Fife KY16 9SS, Scotland.
