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Bleistift HQ’s failed attempt to improve paper testing 4

Earlier this year I tried to reduce the human element that is part of my pen and paper tests, e.g. those tests with violin plots. The aim was to make these tests more accurate and reproducible. Plotters are expensive, so I thought I try the :Move mini, an add-on for the micro:bit.

The micro:bit is a small ‘computer’, half the size of a credit card and is used in computer education in the UK. The :Move mini is a robot with two wheels that can be controlled by the micro:bit and that comes with a pen holder.

When I programmed the :Move mini I found it quite difficult to get it to draw a straight line and to have the same reproducible movements on paper, so I contacted the manufacturer Kitronik. Michael Lockhart, who works for their customer service got back to me and asked me to send my :MOVE mini in.

You might have seen this video on my YouTube Channel a few months go.

He told me that they

performed tests at a range of speeds, running at full speed the buggy runs straight and doesn’t suffer with one wheel turning at a different rate. You can reduce the speed to slow the buggy, however the more you slow the speed the more likely the buggy is going to drift to one side. Unfortunately this isn’t a fault with the buggy and more with the way the micro:bit is coded.

By using PWM you define how long you want the pulse to be and the gap between this pulse, as the micro:bit isn’t real time, this causes a slight differences in what the two pins are being told, and this always remains with the same pin. As such this results in one of the pins receiving a slightly different pulse to the other and as such at slow speeds there will be a drift. We had this set to pin 1 at 80 and pin 2 at 100, this is obviously just above/below the stop position for a 360 degree servo.

The longer the pulse is made the smaller the issues with the micro:bit is made, as such you may be able to counter out the issue with the micro:bit by setting the servo’s to half speed[…].

The bad news is that I can’t drive slowly or things go wrong, but if I drive fast things go wrong, too – see the video. Maybe if I could get rubber wheels for the :MOVE mini things would work better with higher speeds.

I also had a question regarding reproducibility as I was wondering whether the charge level of the battery will make a difference. Michael told me that..

In short yes that battery voltage would affect the servos, however it is a little more complex than that. So it works like this:
The servo board has a 3.3V regulator on it which then means the servos are provided with a constant voltage from the 4.5V battery pack. This means that the speed of the servos can be more accurate as when you use PWM you are varying the amount of voltage the servo’s are receiving for a given time. So while the combined voltage of the 3 batteries is between 3.3 and 4.5V the servos will run and you shouldn’t notice any change in there operation.

However once it drops below 3.3V’s the regulator will just pass the battery voltage straight through, this means that whatever the voltage is it will be passed to the micro:bit/Servos. This then means that the voltage that the servos will be provided with can alter and won’t be a regulated voltage. As such this could result in them operating slightly differently, this would normally affect the speed of the servos.

Well, it was interesting to find all these things out, but I am still not any closer to a reproducible pen and paper tester (with the use of a plotter, they cost £200 or more). I noticed that there are R2D2 toys that can draw lines. They are slightly cheaper than a plotter but still expensive.

I guess it might take another few years before I find a good solution…

 


The End of an Era 6

This week I’ve been throwing a few things from my office away: stuff, mainly student assignments, that I don’t need to keep anymore.

I’m what they call a senior lecturer here in the UK, according to Wikipedia that’s an ‘associate professor’ elsewhere, and for that reason I’m involved in marking student work. Old assignments used to get stored centrally, but a few  years ago management decided that we should store them in our office1. We only need to keep them for a few years, then we can get rid of them. During my clear out session I came across some of the last type written feedback sheets I made.

Yes, the assignment is to programme a pencil museum (using PHP, AJAX and MySQL). Parts are pixelated for privacy

Our feedback sheets used to be spaced just right for typewriters2 and used carbonless copy paper. They have since been replaced with new feedback sheets that don’t leave space for feedback.

The real feedback is on the pages with code, this is just for the cover page

To celebrate the end of the typewriter friendly era in my place of work I thought I show you how these sheets looked like (cropped for privacy reasons). I sometimes used them with a portable typewriter I bought second hand in the 1980s, but most times feedback was handwritten.

  1. You might think that means we have less space, but management also took our printers and our waste bins away, so that gave as a cubic metre of extra space back. []
  2. but unfortunately no one else I knew seemed to make use of this feature, or if they did it was before my time, i.e. before I joined in 2001. []

Andreas Dorau’s Pencil 7

If you are from France or the German speaking countries you might have heard of Andreas Dorau. He was in the German charts in 1981 with a NDW song (also released in the UK) and in 1996 he made it into the French charts with Girls in Love.

Well, this week he finally made his wish come true and made it into the German album charts (#56), for the first time, with his album “Die Liebe und der Ärger der Anderen”. One of the songs, “Du stehst auf meiner Liste”, even features a pencil, paper, and erasing.

Congratulations!

PS: If you don’t know the songs, they both have a sad ending. In the 1981 song “Fred vom Jupiter” the womanising alien has to fly back to Jupiter because all the earth men are jealous and the 1996 song “Girls i Love” has an even sadder ending.

PPS: eSyringe has a series of videos of Andreas Dorau live in Tokyo. 


Microsoft’s Pen

In the sixteen years I’ve been with my current employer my computer has been replaced a few times, but this is the first time the new hardware1 came with a pen. The new pen even has an eraser at the end.

I guess there will be even fewer chances of marking student assignments with pen and writing feedback with pen or typewriter (our feedback forms used to be spaced just right for use with typewriters, a remainder of the past).  Let’s see whether I’ll like using this pen as much as my analogue pens -I doubt I will2.

  1. Of course not the latest model, but the one from a few years ago, with the smallest RAM and storage configuration on the market []
  2. Maybe because this is quite a low spec piece of hardware the line you draw doesn’t seem to follow the tip if you move fast []

Kenji’s Cat Pencil 2

Earlier this week I had to go to Preton’s1 city centre where I made two discoveries.

Helix Oxford

The Oxford series from Helix (which belongs to France’s Maped, with most or all products made in China) seems to have launched a new vintage range which is available in WH Smith stores.

Kenji

I also discovered what seems to be a local Muji copy: Kenji. The outside looks like Japan’s Muji, but the goods they sell seem to be at least halfway (if not further) between Muji and Denmark’s Tiger stores. When I asked the employee he said the store opened last October.

I assumed this is a bigger chain, but when I visited their web site I was suprised to see that there are only two shops, one in Preston and one in Bury (together Preston and Bury have 200,000 inhabitants). Even more surprising when keeping in mind that despite being small they have a large selection of items, seem to be good value for money, and their web site looks rather good, too.

 

The DS-508

I couldn’t resist and bought a novelty mechanical pencil for £0.80 (~$1; €0.90). It’s the DS-508 from D&S点石. Despite being from a Chinese company the pencil is labelled in Japanese. The push button is the cat’s tail.

 

Like another Chinese mechanical pencil reviewed in the past, the M&G m9, this pencil has a sliding cone. You need about 0.8N for the cone to slide, which means that the sliding mechanism won’t work for most users – unless you hold the pencil nearly vertically. To refill leads you remove the tail of the cat. There is no  eraser.

The jaws of the ratchet mechanism that holds the lead are even metal, so this pencil should last a while before breaking down. For a novelty mechanical pencil, and especially when keeping the price in mind this pencil is surprisingly good.


Please excuse the poor quality of the photos, this blog post only contains mobile phone photos.

Price and exchange rates: June 2017

I have added the DS-508 to my sliding sleeve table.

  1. where I live []