Originally Posted by
edeca
Very good point, I will add some more turns before ordering. I looked at both your design and the one from Gerrie and ended up in the middle. Gerrie has four layers though, so it would probably be best to get to at least 10 turns.
I was confused at first by the best way to use both sides, I assumed three things:
- crossing the tracks on different layers does not matter (e.g. my top left)
- the trace should always continue in the same direction
- there is a single trace with one beginning and end, rather than "doubling up" the trace on different layers
I hope these are correct.
What were the dimensions of your final PCB?
Your trace arrangement is fine. The traces are two spirals in series, joined to each other at the outer edges with a via. The current in each spiral flows in the same direction so the fields reinforce. On the original layout, the spiral on the top layer goes counter-clockwise from inside to outside, and the spiral on the bottom layer goes counter-clockwise from outside to inside. (This can also be clockwise on both, as on your layout.)
Using more than two layers requires fewer turns on each layer, while making the X-Y dimensions smaller requires more turns.
You can use the original PC layout as a starting point for a new layout, especially if you are using FreePCB. The original layout is 1.25" square, the same as yours.