Sunday, January 25, 2009

Clean Power

As part of my guitar effects house-cleaning I thought I would build a real 9VDC power supply rather than the mish-mash of batteries and hacked up wall wart that I use now. I also wanted to learn Eagle as it is always touted as the best, free CAD package out there for hobby electronics. I decided to start with this circuit for an adjustable power supply from Tonepad. Tonepad is great, but I think a lot of their layouts aren't the greatest since they don't try to minimize the amount of copper you must etch off of the copper-clad board. As a result, etching takes longer and you end up using more ferric chloride. This isn't really a concern, but I figured I could come up with an more optimal layout, and basically used this as an excuse to learn Eagle. I've never actually designed a single layer PCB before (my previous designs have been double-layer boards, ordered online from ExpressPCB), and never realized how difficult it was to route things given the single-layer design constraint. As a result, it took me much longer than I expected. I ended up with this layout:

I think it turned out alright, and I learned a lot in the process. Eagle is definitely much harder to use than ExpressPCB, but it has quite a bit more functionality (most of which I don't know how to use).

I also decided to experiment with Sharon's scrapbooking machine while I was at it. Instead of trying the usual toner-transfer method of etching the PCB, I thought I would try cutting the mask out of vinyl and etching the board that way. I loaded up her Klic-n-Kut, and cut out the layout which I had exported from Eagle.

I then applied the mask to the copper clad board. If you look really close you will see that the mask produced by Sharon's machine actually isn't all that great. I am on the very edge of the capability of her machine in terms of size. Basically, the size of the pattern I am trying to cut is so small, the machine can't produce it (the knife works by pivoting around a slightly off-center pivot point, which is about the size of one of the corners in my layout). There may be various ways around this, but I may just end up going back to the toner-transfer method for future layouts.

After about 15 minutes in ferric chloride, I had a PCB for my power supply.

All that was left was to drill the PCB and mount the components. After a bit of smoke (I soldered in one of the diodes backwards...oops!), the result was a working 9VDC power supply for my future guitar effects projects.

From Effects Pedals

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