I've got an Etch...

This post is somewhat of a continuation of my Arduino-based Flow Meter project (FlowBot maybe?), but also a side project. As I mentioned, I'd like to house the device in a 1" PVC pipe. I managed to draw up a design that's about 14cm long that fits nicely in the PVC.

One issue is that my current rig seems to be quite fragile - I'm having to worry about knocking the connections as it slides in the housing.

So I decided to design my first Printed Circuit Board (PCB). Spent some time trying to teach myself EagleCAD, which will eventually need to be revisited, but for now I'm just using the free software ExpressPCB. Rather than automatically mapping the traces with the more sophisticated software, I manually laid out the connections so that everything fit just right - definitely a puzzle!

Once I had the board designed, I needed to figure out a way to etch the copper. Looks like there's 1,001 different "best" techniques for this, so I went somewhat rogue. (And here I am posting #1,002) The basic idea is to transfer the above image onto a sheet of copper that's fused to an electric insulator (the base PCB material). With the image serving as a mask, you drop the PCB into some corrosive chemical to dissolve away all the exposed copper. The result is that wherever you put your image, the copper remains and can serve as a connecting wire or "trace."

I chose to use the Toner Transfer Method - whereby you print the above image with a laser printer on some material that the toner doesn't readily stick to. I used the *normally trash* side of printable label sheets. You then iron the image on to the copper surface as you would a temporary tattoo on a robot. Lots of heat and pressure (I forgot to take any pictures of this stage). It worked quite nicely, but note that with this method its tough to have traces any narrower than ~0.5mm, but that also depends on factors like the resolution and toner density of your laser printer.

Once the image is ironed on to the PCB, you can touch it up with a fine-tipped sharpie. All your traces should be continuous. If you allow the etch to cut any of the traces you wont have a working circuit, so be precise here. I found that if I made any mistakes with the sharpie, a fine-tipped cotton swab (the extra pointy danger q-tips) dipped in acetone allow for some fine-tuned "erasing." I also don't have any pictures of this.

We're finally ready to etch! I happened to have some 1M HCl from a chemistry workshop I teach, which I mixed in equal parts with 3% Hydrogen Peroxide. DISCLAIMER!! Do your research here. You're making a corrosive solution, so take all necessary precautions. Be smart, be safe, wear all appropriate protective equipment and give yourself some ventilation. I've read you can also use distilled vinegar with peroxide and salt if you're looking for a less caustic solution, but it takes a bit longer. With any chemical method - even the vinegar approach - you must consider the toxic dissolved copper anions in your solution after you're done etching. DO NOT pour this down the drain. You can pull the copper out of solution by dropping in some aluminum foil - but again, do your research. Anyway, TIME TO ETCH!

It helps if you rock the container wile your PCB is etching - you're essentially flushing away layers of copper and exposing new atoms to fresh etchant - just make sure to not splash it around. After about an hour I had a nicely etched PCB!

It turned out quite well for a first attempt, but theres definitely room for improvement - I think in particular the toner transfer method. Just as temporary tattoos never really work JUST right, this method had some core flaws that make it seem like there might be a more sophisticated option.

I just ordered one of these promising little laser engravers (1000mW) for $80 on Aliexpress. The laser wont be strong enough to etch the copper itself, but I'm thinking it can etch a layer of paint on the surface - which should be able to make much straighter/thinner lines than I could with toner transfer. Should be a lot of fun! I'll add to this post with any new developments (which may include hacking the Neje to support larger items).