Building the PC Power Monitor

Ok, D-Day. Time to dig up my Press-n-Peel PCB transfer film and Ferric Chloride.

In the mean time I added a jumper to the circuit design so I can disable the buzzer if it became too annoying.

I currently have a HP 2840 multifunction printer that works reasonably well. However, to save the PnP transfer film, I thought I would cut it into A5 sized sheets. During testing on plain paper, I found that Eagle or the HP print driver would enlarge the circuit board, but when printed on a A4 page it comes out at the correct size. Hmm! I could have played around with the Eagle scaling factor, but ended up printing both the Power Monitor and the Power Distribution layouts onto one sheet, rotating the sheet and feeding it back in for the next one etc. Next time I will try playing around with printing the designs onto paper, and cut and pasting them onto one sheet of paper, then photocopying that onto the PnP PCB Transfer film.

I wasn't happy to find that the toner seemed to have spread out (electrostatic bleed?), beyond the layout. I didn't take a photo of the effect - I should have in hind sight, just to be able to show what it looked like. This had the effect of stuffing up the circuit layout. I cleaned off the old spare cloths iron that I have kept for shed use. Initially I set the heat setting to near cotton/linen. I processed the smaller Power Distribution board first, but found that the heat setting was too high, and apart from partially melting the plastic, the toner seemed to go a bit blotchy. Apart from looking dodgy, it wasn't anything that I couldn't fix up with a scraper. For the Power Monitoring board I turned the heat level down to between wool and polyester and since I had a layer of paper between the plastic transfer film and the iron, I rotated the iron around a bit to help spread the heat out. This worked much better, as the first board ended up missing transferring a corner or toner due to the lack of heat. It took me a further two hours to scratch off the extra toner and clean up the layout.

After dinner I found the bottle of 34 year old Ferric Chloride chipped some chunks off into a small plastic bath of water and placed both of the boards into the solution. I also added a dash of Hydrochloric acid the help the process along.

While waiting for the exposed copper to be etched away, I worked on adding on some mounting brackets for the LCD screen. The brackets are just old recycled computer PCI slot blanks (I knew they would come in handy for something down the road). At around 22:00, and after one and half hours, I gave up for the night, pulled the boards out and washed them down. It took a further three hours the next morning to finish etching the boards. One can't rush this. I suppose I could purchase some Ammonium Persulfate, as that would speed things up. Here is a photo of the boards after etching and the pads cleaned with acetone:

Next up was drilling and mounting/soldering the components. Pretty standard, except this was my first go at soldering a surface mounted component to a board. After mounting a few components I realised that it would be best to clean off the rest of the toner too. Yes, a good magnifying lens is handy when mounting the SOIC-8. Here is the end product:

And lastly, recycle and reuse... here is a shot of the new LCD holder brackets:

As mentioned in the comment back on the design-II blog, there where two mistakes made on the layout:

1. Eagle didn't display the PICAXE or the 7805 regulator pads from the top, so they needed to be mounted on the solder side of the board. Not ideal, but hey, it still works. Mental note made to watch out when I do the next board layout.
2. In the photo of the board layout above, in the bottom left hand side are some header pins. Eagle let me layout a copper sheet that esentually shorted a data pin to ground. Normally it's very good at not letting you do things like this, but it didn't catch it out. I will need to experiment with Eagle a bit when I do my next design. I fixed this with a quick route with my dremal tool.

Lastly I have included a photo of the power distribution board, before it was etched. Youmight be able to see the scratchings I made as I cleaned up the layout. Also note the blotchy look of the tracks due to the high heat and preasure that smudged out the toner and the missing toner on the top right hand corner:

Now I just have to cram both of the boards into the PC housing.  That should be fun.