I built a linear actuator using the lead screw from a Black and Decker workbench and a gearbox housed in the case of an old CD drive. I haven’t quite decided how I’m going to use it but it seems to work reasonably well. I was originally planning to drive it with a stepper motor from a printer, but it didn’t provide anywhere near enough torque once everything was bolted together. I now need some kind of encoder to give feedback on the position of the screw.
This is the tidiest my bench has ever been.
I ordered 8 very small componants from RS yesterday. They arrived today in some shockingly luxurious packaging.
NeverMung is almost an actual thing which exists.
It turns out Maplin is just as shitty at spraying photoresist as I am and the really important part is exposure. So now I have an ugly but probably functional board, made all by myself. All that remains is to add a couple more parts I had to order and solder it up. Oh and code. Lots and lots of code. But I can do that in bed.
I etched one to see how it would come out. Parts of it are pretty good, but there are places where the template was out of focus. I think the staples stopped it from sitting flat.
The pre-coated boards arrived from Maplin today. I cut one to size, conservatively exposed it for less than two minutes and dunked it in developer. All the resist fell off within seconds. Fuck. That developer solution must be waaay too strong. Luckily I bought three boards, but they cost about £3 each.
Maybe I need to invest in some scales and a thermometer.
Things have been quiet ’round here recently. I’ve been working on some things I could have posted, but the real has been getting in the way. I took a few months off from NeverMung to give my head a chance to clear from the intricacies of the TCP/IP protocol. I still haven’t looked at the code again but since last week I’ve been working on putting together some real hardware to work on. Getting a single prototype PCB fabbed is prohibitively expensive, especially when there’s a good chance it won’t work the first time, so I’ve been working on making them at home. I had fun getting the board layout done in Kicad. It was the most complicated design I’ve ever made but I managed to fit it in the space I’d allowed myself with some awkward stitching around the SD Card.
Back
Front
Actually producing the board has proved far more challenging. I already have a UV exposure box I built a while ago which works pretty well when used with a mask printed on ordinary printer paper with an inkjet. I began by using tracing paper, but it was too difficult to get a dark enough black.
Since, as I’ve often mentioned, I’m a pathological cheapskate, I opted to use spray on photoresist instead of the more expensive pre-coated boards. This has been the downfall of the whole project. It is incredibly difficult to get an even layer of the right thickness on both sides of the PCB, especially when you’re working inside a homemade fume cupboard in a darkened room laden with solvent vapours from the resist. I have spent the last four days repeatedly cleaning, spraying, baking, exposing and developing the board and tweaking the process every time it didn’t come out right. The closest I managed was almost perfect in most places with very clear traces in the developed resist but a few uneven patches in the resist rendered the whole thing useless. Eventually I gave up and ordered some pre-coated boards.
Aside from NeverMung, I’ve also been restoring an old Zeiss microscope from Ebay, and messing about with web security and SQL injection, which is a topic for another post if I get anywhere interesting with it.
See you soon, I hope.
It’s early in the morning after boxing day. I’ve spent the at a party with relatives, which was enjoyable, though it has left little time for hacking with my new toys. I did get a chance to see my first Kinect, though which would make a fine set of eyes for a robot, thanks to the tireless efforts of some reverse engineers. Nevertheless, I did get a couple of hours to poke around inside the glitzy white innards of the beaglebone I was given for Christmas.
After a multimeter, an oscilloscpe is probably the most useful electronics intrsument, at least within an amateur price range. Since my own price range is smaller than most I have had to shop around a bit. Anything which is actually guarenteed to turn on, for example, is far too expensive. This has led me to the strategy of buying a series of complete beaters and boat anchors in the hope that one of them will be sound enough to repair. As a result, the last few weekends have been a mess of corroded PCBs, capacitors and archaic schematics.
Beater the first:
My first buy was a Telequipment D1010; a fairly compact scope of late 1970s vintage. Things looked promising at first. I turned it on a pressed the beam finder button, which produced a sharp green trace…along with a loud screaming noise from somwhere near the back of the case. Opening it up revealed no obvious signs of arcing, though the mains supply board was badly corroded. I cleaned up the boards and tested nothing was connected to anything that shouldn’t be, reassembled, and promptly blew a fuse. It was cramped inside the case and densely stuffed with wires which must have led me to bridge a solder joint somewhere when reconnecting the supply board. When some replacement fuses arrived I tried again and again. Eventually I managed to fix the short, but by this point pads were beginning to delaminate, wires were getting short and screws were getting lost. It powered up again but the trace was completely out of focus, far beyond the range of the adjustment dial. It still screamed, and I’m beginning to think the sound was comming from the secondary arcing in the transformer. By this point I was sick of the sight of the thing so I pulled out the transformer for another project and put it on a shelf.
Guts, guts, guts!
Beater the second:
My second scope is even older, from around 1968. Interstingly it has a combination of valves and transistors, placing it at the turn of the tide when solid state electronics began to dominate. It arrived only last week, and I’ve only had a chance to look at it today. It’s far easier to get at than the last one, with side pannels which just slide off, as opposed to the entwined mass of plastic, sheet steel and bags full of screws which enclosed the other one. The transformer is a baffling affair with many taps on either side. There’s no switch to select input voltage, so you’re expected to work things out for yourself. According to the manual, for the OS25, there’s supposed to be taps for 110, 220, 230 and 240 volts, but on mine, which is an OS25A, it only seems to go up to 120V. Other than that it seems to be identical. Maybe the ‘A’ model was an export version for America. I think the wire colours in the flex (which had been hacked off at some point) are those used in there. If so, it’ll need another transformer to step down from 250V to sissy American 110V mains. (Bah! I touched a 250V terminal it and it was fine, once I’d recalled which way was up).
Anyway, pictures of the second scope coming soon. There’s some beautiful old circuitry in there to gawp at if you like that sort of thing.
I’m getting distracted by diversions; this is no good. I need some better ways to bully myself into coding more. I’m thinking either some kind of reward system, that Firefox add-on that blocks selected sites at certain times, or possibly electroshock therapy. The thing is I’m really good at Not Coding, since I’ve been practising it all my life. In fact I’m successfully doing it right now. The problem is, microcontrollers need code to run , and not coding isn’t a very efficacious way of producing it.
Even when not actively Not Coding, real life tends to get in the way. I need to find a cave somewhere where the rocks are naturally caffeinated and live there until the firmware for NeverMung is done.
