Category Archives: Mechanical

Desktop Speaker Mounting

Problem: Kim’s desk has an open back where her desktop speakers are placed, and they keep falling off the desk. Solution: mount them higher up off the desk, on a section of perforated metal. But first, I needed to modify the speaker cases with some mounting hardware.

Various stage of completion

I first superglued some #10-24 nuts to the top of two of the speaker case’s clamshell boss screw holes (to keep them in place), then heat them with my hot air soldering station at 200°C and pushed them into the melted plastic. This created some secure embedded threading to screw a #10-24 bolt into, through the perforated metal sections.

Mounted, quick and crooked

DIY Bubble Etching Tank

I finally built a simple bubble etching tank; I’ve seen people with them all over the place in the past, but I just haven’t had the desire to put one together until today. In the past, I’ve been etching my PCBs by just filling a pyrex tray with etchant, dropping the masked board in and manually agitating with a foam brush.

This new piece of equipment has these advantages:

  1. Less etchant required; the vertical tank takes up less volume and thus it is more space efficient.
  2. Air agitation; the bubbles oxidize the etchant, which allows it to more effectively etch away copper. It also creates turbulence in the liquid that helps etch very small areas.
  3. Less manual interaction; the acid in the etchant is toxic stuff, and I really need to be more careful than I have been in the past.

The tank is made from some pieces of spare acrylic sheet I had, which are put together with acrylic cement and the outsides of the joints are reinforced with hot glue (just in case). I had an old aquarium air pump around and carefully hot-glued the end of the tube across the bottom of the tank through some holes drilled into the edges; I then carefully poked holes into the tube using some very small-diameter drill bits. Of course, I tested it with water before trying it with the cupric chloride etchant seen in the photos. I found that there were a lot of droplets splashing out of the tank, so I made a small lid with a spare IC storage tube. The whole construction took a total of two hours.

UPDATE: I put together a small, adjustable acrylic rig to top the tank and hold the part being etched in place.

The green top is a piece of junk acrylic sheet that I found and drilled a series of holes into. The sticks are 1/8″ squared acrylic rods pieced into an edge and covered in double-sided tape (for some extra tackiness); the ends that meet the green top piece are sanded down to round pegs that compression-fit into the holes, which allows the spacing to be adjusted for any size board that may fit in the tank. Small holes are drilled in the pegs so that small screws can be set as an added safety measure should the weight of the board cause the peg to slip, but I’ve found that it isn’t really necessary (maybe for larger boards). In fact, the actual problem is that even the thicker (3.175mm) boards I am etching for my microwave antenna array project are able to fall off the holding rods and down to the bottom of the tank if I am not careful.

So far, the whole setup seems to work well for both developing photoresist (why didn’t I think of that initially?!) and etching boards. The only complaint I have right now is the uneven bubble cover; if the board is not moved around occasionally, the parts in the path of the heavier bubble streams etch faster than the less-covered areas. Etch times for cupric chloride etchant seem to be about 15 minutes for 1/2-oz copper and up to 90 minutes for 2-oz copper (ugh).

DNA Model

I made a DNA model with steel wireframe, LED base pairs, and control circuitry to flash individual pairs randomly at a variable rate – X-Mas gift for my Mother. Just another week of Winter break!

This is, unfortunately, the only good picture I have that is representative of the final form. While I started with the intention of documenting the build in its entirety, I quickly realized it was taking me longer than expected and I had many other things to take care of simultaneously, so I pretty much stopped taking pictures after this one.


I built a model TARDIS for a friend’s birthday. It even has a light on top that blinks at roughly the same frequency as the real one! I made it with a simple CMOS inverter oscillator circuit, 3-AA batteries, and a power switch. I had ideas for some other features, like sound triggered by pressing the “St. John Ambulance” logo on the front and a light-blinking sequence that would basically simulate a takeoff; but that would have been a hell of a lot more work and possibly would have kept me from finishing it anytime soon.

Panel Progress

I hate wasting time, effort and money, but that doesn’t stop me from doing so. I finished laying out, drilling, sanding, and polishing the rest of the front panel for the synthesizer. I also started labeling it by using Gimp to write out and reverse my text on an overlay for some “clear” (eh, close enough for what I’m doing, but they really should call them “matte”) Avery shipping labels that I bought on a whim. Overall, it was not an easy task, particularly when it came to cutting out and sticking the labels to the back of the panel; the results aren’t that great, but still better than anything that I’ve made before. :P

Unfortunately, I’m seriously contemplating redoing it a different way. I have already traced the holes onto some paper backing and scanned them into the computer; from here, I’m going to get some full-page “clear” printer labels and do pretty much the same thing as before, but to whole groups of component holes that correspond to each individual module. I feel that this tactic will produce the best results, especially considering how crooked a lot of the labels I have on there are right now.

As soon as I have this part of the whole project complete, I am going to get going with the soldering; I’m still waiting for an order on some specialty components that I need for the Delay and the Sample and Hold modules.

On a side note, for some reason I’m already thinking of what I’m going to work on when I’m done with this project; I’m going to get started on a true modular synthesizer cabinet! The acrylic panels that I got from US Plastic turned out to have an unmentioned blade tolerance of 3/16″, making them pretty much unsuitable for building a new case that would have a chance of being better than the one I already have for this synth. Fortunately, I can still use them to build rack-mounted modules for a true modular system (in so far as I know at this point, that is). ;D

I can always order proper material to rebuild the case once I have some money later in my life.