Engineering

Like many ageing Honda Civics our VSA and ABS lights have been coming on sporadically for the last few months. Now they’re stuck on all the time. First I suspected the battery, so I duly measured the no-load voltage (~12.6V: not great, but not awful either), the voltage dip when running the fuel pumps, (~11.6V) and the voltage dip when starting (briefly around 10V, but I didn’t have a scope on it). [Read More]

Refrigerate in peace, OpenFridge. The hardware OpenFridge was controlling is no more. It now looks like this: Heat Exchange Door Obviously, it should not look like this. What follows is a post-mortem, because it is worth learning from one’s mistakes. The final moments of a fridge After fixing the defrost I did not get around to replacing the blown thermal fuse. The Chinese sensors were supplied with some kind of wire which breaks if you so much as look at it, and I was afraid I would knock the wire at some point and crash the system. [Read More]

Exactly how flat does a sharpening stone need to be? Exactly how flat, for that matter, does a plane need to be? I’m on holiday. Here is a toy plane, a soft building block, and a half brick (not cut by me): The plane started out rather rusty, as did the iron (why do I always forget to take ‘before’ photos?). The plane sole, lubricated with water, was used to flatten off the soft building block, and it was then used to take the rust off the iron. [Read More]

What do you do with a broken zipper? Especially early in the morning (i.e. around 1am). Here is one way to repair a zip, preserving the latching effect to stop it falling down by itself. The wire rope (from ordinary copper stranded hookup wire) pulls the latching tooth, and the fairlead (made from two very small screws and some more wire soldered in place) converts enough of the tension into downwards force to move the zip. [Read More]

OpenFridge has been running the fridge since the first post, which apparently was in January. In that time: The fridge has been very cold (in fact so cold I increased the setpoint to 5 degrees and moved the sensor to the bottom) The freezer has been cold, as desired The controller reboots pretty frequently The controller sometimes loses the network connection and can’t allocate enough ram to recover it The controller occasionally latches up entirely, even with the software watchdog enabled, and refuses to respond to serial commands. [Read More]

Hardware So we have five mains circuits: the lamp, the fan, the heaters, the compressor, and the ‘superfreeze’ button, which I think just adds the starting coils permanently. The original controller only switches four of these on the board (the superfreeze is a manual switch), and uses triacs for all except the compressor, which has a 10A relay. Of course, that requires the controller to be attached to the AC neutral, which isn’t a great idea with exposed hardware like a prototype balanced on a fridge. [Read More]

We have a Hotpoint FFA52 fridge-freezer. It has previously given much hardship. It no longer works. Here is a graph of a non-working freezer: I don’t mind a bit of swing in the temperature, but that’s all over the place. In the meantime the fridge compartment turned into a freezer, albeit not a very good one. Time to take it apart and see what the problem could be. Cooling System This fridge-freezer has one fan, two thermistors (one in each compartment), one heat exchange (at the top of the freezer compartment), a duct around the heat exchange/fan which causes air to be drawn from the bottom of the freezer compartment and blown out at the top, recirculating via the door, a ‘superfreeze’ button which causes it get colder quicker (or possibly just colder) and is to be used ‘when the ambient temperature is below 16 degrees or you want to freeze fresh food’ and should be used ‘only for 24 hours, but always if the ambient temperature is below 16 degrees’, a light (in the fridge compartment), a door switch (in the fridge compartment), an uncalibrated knob to set the fridge temperature, and a power indicator, which never comes on. [Read More]

Moving is not much fun. Moving pianos is even less fun: you have all the difficulty of moving a 300kg object coupled with the worry that you’ll twist it out of shape, drop it, strain it, or just shake it too much. Moving, however, just round the corner—700yds, according to Google—is at least easier than moving halfway round the world. But moving a piano 700yds is not apparently any easier than moving it 300 miles: you can’t wheel it, not on those little coasters, or even on a furniture dolly. [Read More]

I have a piano to tune. And also to restore: a few hammer shafts to bend, hammers to file, a bit of crud to clean out, bridle straps to replace, etc, etc. The piano cost £40 from Ebay and is in remarkably good nick, and any piano is better than none! But an out of tune piano is no good. Now students, I feel, should not really spend money having their pianos tuned—at least, not students of Theology. [Read More]