I mentioned in Making Ag/AgCl electrodes that I was not really happy with the holder I had made for 18-gauge silver wires for Ag/AgCl electrodes. I spent some more time thinking about the problem and came up with a different design, using 24-gauge fine silver wires.
The picture to the right shows the new design. A silver wire is wound around one ear, through the “armpit”, and back up to the same ear, where it is wound again. Alligator clips can be clamped on the wires at the ears, to make the transition from silver to copper wires. The left and right wires will be parallel, 2cm apart, and can be dipped to a depth of 1cm, 2cm, or 3cm (immersing 2cm, 4cm, or 6cm of wire on each side). The feet and body are narrow enough to fit in a standard 10 oz. clear plastic cup. I envision using the holder by winding the wire, resting the holder on the bottom of the cup, and carefully pouring in liquid to the desired fill level.
The picture is derived from the SVG file that I plan to send to the laser cutter to cut a holder out of acrylic (wordpress.com doesn’t allow me to upload SVG files). In the original SVG file, the thickness and color of the lines indicates which lines are to be used for cutting and which for etching—I had to fatten the lines a lot to make them visible in the PNG file, as “cutting” is signaled by red lines ≤0.001″ wide, which would be far less than a pixel in the PNG file.
I drew the outline with Inkscape, but the conversion to PNG was rather awkward as Inkscape’s conversion to PNG was awful for such thin lines. I ended up putting out PDF from Inkscape, using Photoshop Elements to rasterize the PDF, then using blurring and level changing to get fat lines.
I’ve never used a laser cutter, so I’ve sent e-mail to the Mechatronics instructor whose classes use the laser cutter, in hopes that he can provide an undergrad to walk me through it the first time. I also hope they have some scraps of acrylic that I can cut out one prototype from, to see if the notches work well enough.
Testing the prototype will probably be done with copper wire, since I don’t have 24-gauge silver wire, and it will take a while to get some. If it works ok with copper wire, I’ll go ahead and order the silver wire, get some ¼” acrylic and cut out a dozen holders for the lab (plus a couple of spares in case someone breaks one).