Interesting Video Camera Project

Take a look at this . The brush itself seems almost trivial. It looks like a “web cam” with a brush around it. What isn’t trivial is the big touch sensitive screen!

Very cool idea though. I wonder how you could adapt it to something pen sized on a standard LCD monitor. Come to think of it, I wonder if a regular light pen would work with an LCD since there really isn’t any “raster” as we know it — is there?

Read Quadrature Inputs Easily

Lots of mechanical devices (like mice and shaft encoders) output quadrature signals. This is just a fancy way of saying that you have two signals and whichever one comes on “first” means something. So in the picture, you can see a mouse encoder wheel moving on a single axis counter clock wise. If it were moving clockwise channel 1 would come on before channel 2.

This is a natural byproduct of how the optical encoder wheels work. They are offset a little from each other, so the slots in the wheels are aligned about like the pulses in the oscilloscope trace shown.

The PAK-VII’s primary purpose is to measure pulse widths, but with very little effort it can also measure quadrature inputs. Want to know more? Read .

Neat Trick: Pesky Laser Printer Springs

I have a great HP4000 LaserJet printer (similar to a HP4050) with duplexer and it has run like a workhorse for years. Lately, though, the manual feed tray has been cranky. It likes to pick up more than one sheet. So off to eBay to find a set of replacement rollers. Cheap enough. However, the vendor I bought from had promised online video instructions and the videos were “temporarily unavailable!”

The printed directions covered how to do the roller, but not the pad that catches the paper from underneath. A quick Google (when did that become a verb) found some instructions from a different company. Getting to the plate is an exercise in brute force (I’m guessing an HP tech would disassemble half the printer instead). Once you get the plate off, there are 3 little springs underneath. One is a little fatter than the other two which are about like ball point pen sprints. The bigger spring sits in a little well. But the other two just rest on small plastic nubs.

This is a problem! Because of the tight clearance you have to twist and turn the piece to get it in and the springs fly out — usually into the printer where it takes tweezers and patience to retrieve them.

More Googling. Everyone has the same problem. The springs are almost impossible to reseat I read over and over. Finally I hit upon a plan. I used a small bit of hot glue to hold the springs to the nubs on the pad. I reasoned that if it didn’t work, the hot glue would come right off again. Well, this was a great idea! With the springs secure, you could twist the whole assembly into place, seat the springs on the other side and pop the whole thing into place.

I have a feeling this would work in many places where springs are used. Just get a small amount of glue so you don’t jam the spring other than where the little plastic nub is anyway.

And the paper feeder? Just like new again!

Strange Problem

I’ve had issues with all my sites lately including this one that have seemed “strange”. Well I know what’s happening now, but not why. For some reason, it has become nearly impossible to create a file or a directory with a purely numeric name. Using touch, mkdir, or even a C program to call open or SYS_open fails (errno==2) if the file name has nothing but numbers in it. Any file name that has at least one character that isn’t a number works like you’d expect. This happens on all file systems.

I’ve upgraded the kernel. The fact that it occurs on all file systems and even when directly calling the kernel makes me think it is not the C library or a corrupt file system. There are no loaded modules in the kernel (ext3 built in along with everything else needed).

Here’s a twist. The debugfs program can create directories with numeric names. I assume it is doing some direct manipulation to accomplish this — more evidence it isn’t a file system issue.

Not sure what to do next. My colocators want to wipe my hard drive and reinstall Linux (must be Microsoft trained) but I’ve told them no — I’d figure something out eventually.

Tools you didn't know you needed

See for 5 electronic tools you didn’t know you needed. Truth of it is, except for the IC popper, I could do without these, although your mileage may vary (although I have used real vacuum tweezers and they are good for handling tiny parts — haven’t tried the unpowered kind). The odd tools I use all the time are:

  • Thermal wire strippers — these are amazing. I have a Teledyne Stripall, but they are horribly expensive ($400-600); there are other brands out there too like Hakko. Maybe you can get lucky on E-Bay
  • Vacuum desoldering tools — always cheap on E-bay
  • Jeweler’s loupes – get these cheap at Harbor Freight (around here, they are at the register)
  • Step drill bits – another item that is either ridiculously cheap at Harbor Freight or ridiculously expensive everywhere else
  • Nibbler – One of those metal punches that take out a chunk of metal. Great for making LCD holes and what not (case modders have made these popular again)