Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan
<stefan_trethan@g...> wrote:
> On Mon, 29 Mar 2004 20:37:37 +0200,  wrote:
> 
> > On Mon, 29 Mar 2004 18:07:15 -0000, Steve <alienrelics@y...> wrote:
> >
> >> I just made another board using my vinyl cutter.
> >>
> >
> Is this any faster than drawing it up with a pen?
> it looks a bit crude, i would prefer TT.
> But thanks for the experiment, not many have a vinyl cutter to try...

Faster? Heck yeah! That would be incredibly slow to draw with a pen,
and highly inaccurate. I suppose if you've done a lot. This way,
though, I draw it once, check it over many times, and I know each one
is correct. If I draw it I have all the normal problems with etch
resist pens and I have to check each one multiple times before etching.

I'm without a laser printer at the moment. The one I had before gave
me questionable results that were hard to solder.

I see there is a Brother laser printer at Office Max (or CompUSA?)
that is $125 after rebates. I'm too broke to buy it, though.

> can you explain what the circuit does (if there is a www reference
maybe)
> dopplerRDF... hmmmm...

Sure. It uses two antennas about 1/4 wavelength apart. They are
connected to a 2 way electronic switcher. The output of that is
connected to a narrowband FM radio (in my case an FRS radio). It
switches between the two antennas, when the transmitter is closer to
one antenna than the other, there is a phase shift on switching and
you can hear a tone in the speaker. When it is equidistant to both
antennas, there is no phase difference and hence no tone.

The audio output is fed back to this circuit board where the phase
information is used to determine if the source is closer to the right
or left antenna and displayed on a centered meter, so you get more
than just a simple null indication.

http://home.att.net/%7Ejleggio/projects/rdf/tdoa1.htm

Here's one that only gives two ambiguous nulls but is much simpler:
http://home.att.net/%7Ejleggio/projects/rdf/tdoa2.htm

I thought about building the simpler one, but these will be used by
non-nerds and the few I talked to had a hard time with the idea that
they'd know it was either directly in front or behind, but not know which.

Later I plan on making one with 4 or 8 antennas with a ring of LEDs.

We can continue this on Electronics_101.

Steve