MITx 6.002x week 9 – the school of hard sums

This week’s theme on 6.002x was hard sums. Second order differential equations to be precise. However, for anyone still struggling to get through the lectures, don’t give up! It turns out that most of what we’re expected to do is find the characteristic equations of second order circuits – and that’s all. Certainly none of the lab work or homework required any difficult calculus.

Being exposed to all the maths was simply meant to be good for the soul apparently. I suppose that it does make sense to have at least a vague understanding of why circuit problems involving resistors, inductors and capacitors can be solved using just the characteristic equation of second order differentials, even if all the maths made the lecture sequences for week 9 pretty daunting at first.

Something else I learned this week was that unlike the rest of the world, electrical engineers write the square root of -1 as j, rather than i. Seeing j used in this way had me reaching for my favourite Internet search engine to make absolutely sure that I hadn’t missed something important since I took maths A level! I guess that it makes sense to do this so that it doesn’t get confused with the symbol for current. On that basis, it makes it even more of a shame that the subtle but important differences between VI, vI, vi and Vi when scrawled in the hand of Professor Agarwal are often lost. One conclusion that I’ve already drawn from this course is that it’s amazing that any electronic circuits ever get built correctly, given the huge potential there is for errors in notation.

Anyway, I’m hopeful that there will be no more hard sums on this course. On second thoughts, that may be somewhat of a vain hope …

MITx 6.002x week 8 – just about keeping up with the schedule

Having basked in the afterglow of a successful midterm exam for a little while, I returned to week 8 of the course on Sunday. The lecture sequences were on step, ramp and impulse inputs to RL and RC circuits, followed by a sequence on digital memory.

The first sequence of week 8 (S15) is a good example of a part of the course which really needs revising for online consumption before it’s presented again. The video lectures for this sequence were overly long and repetitive – making the whole experience boring (rather than “fun” or “amazing” as we’re always being told). As a result, it took substantially more than two hours just to watch the 27 separate videos (let alone understand their content). I really believe that the material could have been easily and better explained in half that number in 45-60 minutes. Slower is not always better – even if for some electronic circuits it may be!

It seems I wasn’t the only person that felt this way about this particular sequence as its provoked similar consternation in the course forum. There’s nothing new there – OU students were (and probably still are!) always good at voicing their feelings about pedagogic style in the module forums too.

However, what is particularly impressive on this occasion is the positive reaction of the 6.002x staff to the criticism of this particular sequence – well done, THuang! I’m not certain that other institutions would have reacted quite so well to student feedback of this type.

Anyway, on to the week 8 labs and homework. The lab was fine – once I’d realised that the value shown on the graphs didn’t relate to the end of the curve as I’d assumed – but the portion of the graph that was marked with a very faint dotted line! I wasted a couple of hours trying to figure out what I’d got wrong with my maths …

I found the homework questions for week 8 rather tricky on the whole. Part two was relatively straightforward, but part one was especially frustrating (though I got there in the end) and part three, on a memory circuit, was somewhere between the two in difficulty.

I got around to starting week 9 yesterday evening by attempting the lab – which I was able to complete without studying any of the material beforehand. Clearly, my intuition is being developed, just as Professor Agarwal promises!

The homework questions look rather more challenging though … time to get back to the video lectures. Fortunately, there are only 18 to watch in sequence 17!

MITx 6.002x week 7 – no hard algebra or maths for once!

I wrote yesterday that I was concerned I needed to complete the week 7 materials, homework and lab this week, as well as tackling the midterm exam. However, encouraged by some of what I saw on the 6.002x forum yesterday evening, I dived straight into the material this morning and attempted the homework and lab this evening.

What a relief!

MIT must be feeling kind. Or perhaps the midterm exam really is going to be a stinker …

MITx 6.002x week 6 – the midterm exam approaches

Having been a little bit ahead of the curve after completing the week 5 homework and lab, I’m now somewhat further behind than I ought to be, mostly because I took the week after Easter off on holiday. The course definitely hasn’t been plain sailing for the last couple of weeks. I wrote that I’d struggled to get the answer to the penultimate homework question in week 5 correct and in the end, I simply had to give up on it. Fortunately,  I’ve found week 6 a little more straightforward, but I’ve been just as frustrated with the maths as I was in week 5.

So my overall progress now looks like this:

MITx 6.002x progress - at the end of week 6
MITx 6.002x progress - at the end of week 6

However, the course is just about to get even more interesting (or rather, more difficult) to keep up with.

This week, as well as needing to complete the week 7 material, homework and labs, I also have the midterm exam to tackle. The instructions on the course website say that the exam will be available from 2200 GMT on April 25th (which I calculate is 2300 BST!) until 1200 GMT on April 30th (1300 BST, I believe). Once I decide to start the exam, I will have 24 hours in which to complete it – and only 3 attempts per question to get the right answer (as opposed to having unlimited attempts on the homework and lab questions). That still seems rather generous however – particularly when thinking back to my OU experience.

I’ll be quite happy with anything over 60%  on the midterm … which will at least keep me in the game for the remainder of the course.

MITx 6.002x – week 5: sharp tools required

Week 5 on MITx has felt rather like revisiting week 4. The main difference has been that rather than using circuits with hypothetical voltage controlled current sources in them, we’ve been introduced to using transistors (or MOSFETs, as the course likes to call them) in their saturation region as a way of achieving a practical amplification circuit.

Even some of the homework on week 5 has had a sense of repetition about it. The first few questions in H5P3 are all but identical to those given as H4P2 last week. Still, I’m not complaining – definitely easy marks compared to the algebraic hell that was H5P1 question 3!

In the end, I decided that after an hour or two of managing to mix up my vINs, VTs and square roots, I’d do the sensible thing. Rather than carry on wasting time in hand-cranking quadratic equations, I downloaded a copy of Microsoft Mathematics 4.0 and let it do the non-value added aspects of the work for me. I’d have willingly paid for it … but it was free! Having this software available also enabled me to work out the partial differential equation required to solve the first part of H5P2 without using reams of paper.

This experience reminded me of the title of a chapter in the Mythical Man Month – Sharp Tools.  In this chapter, Fred Brooks argues that a common set of appropriate tools are required to enable a programming team to be productive. It would seem to me that as 6.002x is attempting to teach electronic engineering rather than pure mathematics, it might be a reasonable idea for future runs of the course to either point students to tools like Microsoft Mathematics or provide an online equivalent as part of the MITx VLE (virtual learning environment). After all, once you’ve identified the two equations from analysing the circuit that you need to solve, the rest of the process is purely mechanical and adds nothing to your understanding.

The only question I now have left to work out is the penultimate one on H5P3. I think I’m trying to simplify my algebra a little too quickly and as a result missing something. However, even though I don’t appear to have the answer completely worked out, I certainly had enough of it present to draw the correct inference for the very last question of week 5.

MITx 6.002x week 4 – slow going on homework 4, part 2

I’m rather cross with myself – and the course question setters this week. Having found the Lab 4 curve tracer exercise straightforward and also having rattled my way through the first two parts of homework 4 (H4P0 and H4P1 on Zener diodes) without too much difficulty, I got stuck on the amplifier questions in H4P2.

Except, I didn’t really. I’d assumed that a couple of decimal places for reporting the bias current would be sufficient … however, the answer appears to require at least 3 decimal places! I spent ages going round in circles, assuming that I’d got my logic wrong (I hadn’t), only to come back to the original answer, which still wasn’t accepted when I plugged it in.

As I’m currently sitting on a train on my way down to London, I took the opportunity to try it again, having noticed a number of people on the forum say that the question was being fairly picky about what precision you used. Sure enough, going to 3, 4 or 5 decimal places on the answer sorted it for me. At least I should be able to finish the rest of the question fairly quickly now and get myself going on week 5. Thank goodness the Easter holidays are this weekend!

My experience does raise an interesting point however. Most practical electronic circuits operate within fairly relaxed tolerances. For example, typical resistors tend to deliver a value within a few percentage points of their stated resistance. Things becomes even more lax when you realise that you are usually selecting resistance values from either the E12 or E24 range and so can only approximate the ideal resistance you’d like to use. But that’s ok, as there is little difference in practice between a current of (say) 0.17499 A, 0.175A or 0.18A. Yet, in the case of this week’s homework, the first two values are considered correct but the third one is wrong (note – this isn’t my actual answer – just an illustration of the problem).

While I understand that the course designers are looking to ensure that students aren’t simply guessing their answers, I think that as a minimum the questions should state explicitly the number of decimal places or significant figures an answer is required to. That way, I could have spent more time this week enjoying the material, rather than assuming that I’d missed something when I’d worked my answer out originally.


MITx 6.002x – week 3: So what exactly is an “expo dweeb”?

It’s just before 11am on Saturday morning and I’m already through week 3 of the course, having successfully completed the homework assignments and the lab. I’m not sure if it’s because I’m now getting into the swing of the material, or because the course has moved onto digital logic and devices like transistors and diodes that I’m comfortable with, but it seems to have become considerably easier going this week. I certainly find it easier to conceptualize these things than simply chasing mathematical formulae around circuits consisting just of voltage and current sources, that’s for sure.

I’m not sure that I really understand why the hypothetical non-linear device that we were introduced to was called an “expo dweeb”. Perhaps it’s a cultural or age thing, but I just didn’t understand why it was called that. To my ears, “expo dweeb” sounds more like an insult than a name for a device. If someone can explain to me why it’s appropriate and/or funny, perhaps you could leave me a note in the comments!

Overall, the lecture sequence did rather drag in places this week and could certainly have used a little judicious editing to remove 20 or 30 minutes of spoken material which really didn’t add anything to its presentation. However, the video demonstration of how linking a non-linear to a linear circuit creates distortion by playing a Britney Spears track through it was certainly amusing. I’m of the opinion that the distortion probably made her sound better, rather than worse …

Onto week 4 I go – incremental circuit analysis, dependent sources and amplifiers are up next.

MITx 6.002x – week 2

I’ve just finished hacking my way through the week 2 homework and lab. This week has focussed on the use of superposition and the Thévenin and Norton methods for analysing linear circuits, followed by a brief canter through some basic digital logic.

Three tasks were set for this week’s homework. The first was to find suitable resistance values from the E12 range to complete a voltage divider, which was relatively straightforward. The third task was to complete a truth table for a digital logic circuit and work out which one of three other circuits were equivalent to it. Again, pretty straightforward.

However, the second task – working out a Thévenin equivalent circuit for three resistors and a current source which was then connected to an external load – took me ages. Not because it was difficult … but simply because I was trying to make the task too complicated! A glass of wine eventually helped me to figure out where I’d gone wrong.

The lab should have been relatively straightforward as well – but again, it took me an hour or so of frustration followed by another glass of wine to realise that I’d been trying to over complicate the solution.

I’m not sure that I’m really enjoying this course at the moment – it’s certainly not as engaging as any of the OU modules I’ve taken. For example, I’m definitely not finding the constant use of slides with a soundtrack, annotated with the lecturer’s illegible scrawl as the primary teaching method particularly innovative or useful for lone study.

Playing in the MITx 6.002x circuit sandbox
Playing in the MITx 6.002x circuit sandbox

However, the textbook which accompanies the course is much better (I may have to invest in a paper copy to write on if I do carry on with the course) and the circuit sandbox they provide is absolutely indispensable for ensuring that you’ve understood the theory and that your maths is correct.

MITx 6.002x – week 1

I’ve just completed my first lab and “homework” for MITx 6.002x – and I achieved a decent result too!

MITx 6.002x - week1 progress

However, before I get too excited, I need to point out that they have a rather odd system of marking assignments – and one that anyone who’s studied an OU course would love!

You are allowed to make as many attempts at each question as you want. Not only that, but it the course software gives you instant feedback on whether your answer was right or wrong. So getting 100% (or close to it) didn’t ought to be that difficult for every lab and “homework”.

30% of the course marks are awarded just for completing these 12 weekly “homework” assignments and labs – in other words, just for (virtually, of course) turning up. This leads me to wonder if the same will apply to the mid-term and final assignments – worth 30% and 40% of the course respectively.

Leaving assignments aside, it’s been an interesting week going through the material. It’s reminded me of many of the things I first learned 30-odd years ago (Kirchhoff’s Current and Voltage Laws, for example) and had since forgotten about. The material has been engaging and even the over-use of words like “fun” and “cool” isn’t annoying me too much at the moment.

I’ve found that other people are blogging about the course too.  For example, Alison Wheeler has written about how 6.002x fails the internationalization (i18n) test. It’s an interesting article, and I agree in principle with all of the points she makes in it.

However, perhaps such criticism at this stage of MITx’s development is a little harsh, and Alison does close her article by partially conceding this point. DD307 “situated knowledges”, anyone? After all, you know before you sign up that you’ll be taking a prototype course, designed by Americans, using material adapted from a “live” (and paid for!) presentation to Americans on MIT 6.002.

For the time being, I’m more than prepared to forgive them for using a 115 feet length of wire in one of the exercises, instead of referring to it as having a length of 35.052 metres.