Re: ATM The project is on it's way

[Dwight Elvey <elvey@hal.com>]

"Ryan Hess" <atmryan@excite.com> wrote:
> According to them, it's not even diffraction 
> limited, it's 1/2 wave.  All the more motivation 
> to get this project on the road.

Not surprised. I'll have to check mine some time to
see what it looks like. I don't expect much.

>    I've sent off for my mirror grinding supplies, 
> and my new spider. 

 I'm not sure you'll need all the grinding stuff.
You can make a polishing lap to bring it to better
than 1/4 wave. There is a trick to remove the
aluminum, some place in the archives. Polishing
will be enough work for you without resorting to
grinding.

>  I just finished making a 
> stepper motor interface for the focault tester.  
> It features 4 pushbuttons, and a stepper that 
> has 200 steps. 

Remember, there are two fine adjustments for the Foucault
tester. The one is the result you put into the programs and
the other is the side to side that is needed for getting
the point that the to and fro measurement means anything.
The side to side is about 100 times as touchy as the
to and fro. You might measure 0.010 inches in to and fro
but need to tweak the tester to 0.0001 inches or better
side to side to get that reading. This seems to be
a common misunderstanding.

>   The LED cost $4, and the 
> second I got home, I wanted to try it out, and I 
> put it on the holder's leads, and burnt it out. 

As I said, in a earlier post, be careful to run these
with a limiting resistor. Even with the potentiometer,
I would recommend a fixed maximum limiting resistor
in series. Remember, the LED can be degraded quite fast
with just a little over current as you found with
the super bright one. Figuring the green
LED at 2.1 volts at 20 mA and the two D cell at 3.0V,
that works out to a value of 45 ohms. This is a hard
value to find but 47 ohm 5% 1/8 watt are common.
Dwight