Building the Digital Compass
A previous entry, discussed building the intial Digital Compass test circuit on a breadboard. Now it was time to design a PCB layout and etch it out. It's only taken 3 weeks to do. A lot of family time over xmas, but I still managed to fit in some time here and there. I had previously came acress a web site talking about using a laser printed image and an hot cloths iron to transfer the PCB layout onto the copper.
Since I had created the schematic diagram in ExpressSCH, I thought I should learn how to use the free ExpressPCB package to layout the PCB. While it's quite easy to learn, I couldn't find a way to print out the PCB layout properly. It came with a grey background! This might be a because you should be using the Express PCB company to make the board. Well, I wasn't going to let that get in my way. I took some measure ments from the correctly sized, but grey print out, and then aquired a screen shot of it from with in GIMP. By playing around with the 'image | Print Size' settings I got it to match the ExpressPCB printout. I just didn't want to have to do it all over again in a different PCB layout package.
I printed it out using three different papers, with one of them being Canon glossy photo paper. Out in the shed, I cut out the PCB size I needed, cleaned it as per instructions, then with the iron on the highest setting, pressed the paper onto the PCB board. It would have helped if I had cleaned the bottom of the iron first, because, as I lifted the iron away, the photo paper peeled away as well, since it was stuck to the iron. After cleaning the PCB again, and the iron, I gave it athother go with a spare sheet. This time it apeared to stick well. I dumped it into hot soapy water, and went and had lunch.
Turns out that the photo paper had something like a plastic coating on both sides, so I couldn't soak the paper and rub it off. I ended up trying to gentley peeling it off. I lost maybe 10% of the PCB layout. Not bad I thought at the time. So after popping down to the local Dick Smith Electronics store and purchasing a PCB layout repairing pen, and a Sharpie pen just in case, I set about repairing the board. What a blotchy mess, I just could lay the ink down fine enough 
Well I thought if I had gotten this far, I might as well trial the etching process as well. I mixed up some 29 year old Ferric Chloride and etched away. After a hour or so, I added a small amount of Hydrochloric Acid to hurry it along a bit. Would have looked nicer, if I had done the toner transfer properly.
Next came the toner removal. Since I didn't have any acetone, I tried Isopropyl Alcohol, Orange oil, Metholayted Spirits and Turpintine. Turpintine, mixed in with a lot of elbow greese removed most of the toner.
This morning I dug up the necessary sockets and components and assembled it. Looks kind of ok from the top. The bottom doesn't look that bad either now that there is a bit of solder here and there to thicken up some of the traces.
This afternoon, I modified the PICAXE compass program to suit the change of pins, and whala! I have a working handheld Digital Compass.
What would I do differently if I had to make it again? Well I will be testing out some different papers before trying to build the next PCB. As you can see, I haven't submitted a photo of the copper side of the PCB. I only made two design flaws on the PCB. I missed a pad (fixed in the PCB layout submitted here), however to fix this I just had to solder the link wire directly onto the resister. The other, I got the secondary Power connector leads around the wrong way. I was going to use a screw down connector, but it has very large pins, and the copper pads weren't large enough, so I ended up using the secondary power supply plug - a Floppy drive power connector. It too, was an easy fix. I just soldered it on under the board. Note: This has not been fixed in the submitted PCB layout. Upon seeing the completed board, I now realise it could have been shrunken by a 1cm or more. Yet another steep learning curve for this sub-project. 
