Thoughtophone

One of the error prone parts of working with the various STM32 micro controllers is that you must configure a peripheral, and in addition, configure specific pins to express that peripheral. This isn't exactly an end product quality issue: it's just a time waster when playing with an evaluation board. If you get it wrong, it doesn't complain: it just doesn't work. Examples often don't explain the relationship between pin settings and peripherals, so you end up endlessly returning to the datasheet, and a table called the alternate function mapping. This doesn't seem to be published in a machine readable format. I thought I would have a quick go at extracting it. I tried tabula extractor , but the results weren't that good. Looking a little further down the list I found pdf-table-extract which the author wrote to extract data from ST Micro datasheets! I haven't tried it yet.

I added some I2C primitives, and to do this I wrote a few helpers to access vectors from Chibios. Then I though: I need a simple way to test this, so I added support for Serial over USB. This didn't work, and when the micro-controller crashed. it took the Linux USB driver with it, and I had to reboot. That precludes using the debugger - since it connects via USB too. So now I have a double defence: The micro-controller dev board is connected to the raspberry pi via USB, and also via serial: the pi has a 3.3V serial port which is perfect for this. You can read some instructions  here . You don't have to reboot though: just do $ sudo init q instead to get init to reload it's configuration. If I have to reboot the pi to get USB access back that will be OK, but using the serial port makes that unlikely anyway. I still haven't used the debugger. My problem turned out to be a cut and paste error: Picobit passes arguments to primitives in 4 global variables. This mak...

I was looking at the Small Scheme Stack a little more than a year ago. I couldn't find the source, so I contacted the authors asking them if it was available under an open source license. Marc Feeley got back to me, asked a few questions about the scheme I planned to use, and suggested Picobit . At the time I abandoned that idea, and finally got around to looking at Picobit about a week ago This afternoon, I've managed to embed it in Chibios. It's already been ported to a specific ARM board, but I wanted to embed it in Chibios to avoid writing a lot of drivers. I've now got a little scheme program that flashes a led on and off on an STM32F4 Discovery board. You can see the fork of picobit here . It's a work in progress: my build in particular is a bit of a mess. Chibios wants your makefiles to follow a fairly rigid structure, and Picobit's makefiles are a little complicated: copying details about the memory map from the vm build across to the compiler. I thi...

I decided to buy this because I wanted to try some milling. I still haven't tried that, but I thought I would mention it anyway - there's quite a lot to like about it as a drill: Up to about 4K RPM, this machine is as quiet as a dentists drill. It's also really quiet actually drilling wood or aluminium (all I've tried so far). Certainly you'll be tempted to just wear ear plugs or skip ear protection completely. At 6K, it's still quieter that the drill it replaces, but you are going to want to put those ear defenders on again. You can get a chuck that fits for less that a fiver. They might be exaggerating by calling it super precision but given how quiet the whole set up is, it must be pretty good. It's easy to switch it out for the collet holder as needed. The collar fits very well, and this makes a noticeable difference to accuracy. I had two goes at buying this. First time was an Amazon marketplace seller using Amazon for fulfilment. It duly arriv...

The blade arrived and I've fitted it. I've spotted a neat trick for measuring the tension of the blade, which involves clamping calliper jaws to the blade and measuring the stretch as the blade is tensioned. here for example. I haven't bothered with this yet. I've tried cutting a few different materials. In all cases, it leaves characteristic vertical groves on the work. On solid pine and MDF, this is very fine: A tiny bit of sanding and it's gone. This is also true of aluminium angle. The 8mm aluminium rod is a little more noticeable. 3mm polycarbonate or acrylic is pretty rough. Not really sure what the cause is. Another thing I've discovered about this saw is the t-track for the mitre guide isn't standard, so it's also not possible to buy an after market mitre gauge. That's a shame, because the provided one isn't great. What I'm working on now is a sort of sliding table. I've cut down a strip of hardwood to fit in the mitre...

Turns out that bandsaw blades are made in very long lengths (10m+), then cut to length and welded into a loop. I don't have the equipment to weld them myself, but there are companies like www.justbandsawblades.co.uk  who will weld custom lengths for you. I can choose any blade 6-13mm width. It seems that I need to choose the the number of teeth by the thickness of the material. This is quoted as TPI. There need to be between 2 and 10 teeth in the material at once. I sometimes cut 1/8" angle. This is cut at 45 ° , so that's 3/16'. I guess that's 12-60 TPI. If I cut 20mm stock, I need 2.5-25 TPI. It seems like my actual choices are 14TPI or 24TPI. I don't cut 20mm stock very often, so it makes sense that's the outer limit of the blade. That means 24TPI. I asked the helpful guys at Axminster, and they suggested 24TPI two, which is re-assuring, but I actually bought the blade from justbandsawblades.co.uk. Sadly I haven't got it yet. The blade guide up...

I've been tinkering with my circular saw cross cut guide. It doesn't always produce great results, and it's because the rails aren't all that strong. They aren't that strong because of the saw's low clearance, which make most conventional jigs impractical. Add to this the showers of aluminium chips it produces, and scatters everywhere, and the difficulty of adequately supporting some materials, and I am less than satisfied. It will still work for the other projects I had in mind for it, but for robotics, I've been looking for something else. I'd nearly narrowed it down to two proxxon machines: The FET table saw and the micro band saw (MBS). These both have there down sides: basically the aren't all that powerful, and can only be used with very small work. Then Axminster discounted there hobby bandsaw to £100, and I decided to buy it. This is not without it's issues. In truth, this was a bit of an impulse. What makes the Proxxon micro ba...