Yes, for a given number of LEDs covering a specified area, there is
no difference in time between scanning and fixed LEDs.
If you buy enough LEDs to expose 100mm by 100mm properly in 60 seconds,
then putting all those LEDs together in a line and scanning will get
the exposure
done in the same amount of time. And the exposure should be more
uniform.
Gus
TISATAAFLP
On Feb 15, 2008, at 12:41 PM, Myc Holmes wrote:
http://hackedgadgets.com/2007/02/24/uv-led-pcb-exposure-scanner/
TANSTAAFL!
Myc
On Feb 15, 2008 2:36 PM, Stefan Trethan <stefan_trethan@...> wrote:
> if you use an old flatbed scanner you'd have all the moving parts for
> that (and the board could remain in place, which is always good).
>
> BUT the drawback is obvious, longer exposure time, ~100,000 times
> longer for the board you suggest to make ;-)
>
> ST
>
>
> On Fri, Feb 15, 2008 at 7:52 PM, agscal -AGSCalabrese
<agscal@...<agscal%40gmail.com>>
> wrote:
> > Why not make a line of LEDs spaced 7-8 mm apart.
> > then push the photoresist board underneath the LEDs
> > at a constant speed ? If your line is 160 mm long you
> > can produce exposed boards 160 mm by 1,000,000 mms.
> >
> > Gus
> >
> >
> >
> > On Feb 15, 2008, at 5:39 AM, Myc Holmes wrote:
> >
> > All of the designs so fr have used a rectangular grid. Since the
> > output is
> > circular in shape, why not take a clue form the honey bees and
set up
> > the
> > LEDS in a hexagonal grid? This should result in more even coverage.
> >
> > Myc
> >
> > On Fri, Feb 15, 2008 at 3:48 AM, agscal -AGSCalabrese
<agscal@...<agscal%40gmail.com>
> >
> > wrote:
> >
> > > Even LEDs from the same batch cannot be trusted to
> > > have the same brightness for the same current. After
> > > they age, it is even less likely that they will match. If you
> > > want them to stay matched you would have to have some
> > > kind of feedback or periodic re-calibration of each LED.
> > > I think that is probably overkill.
> > >
> > > I recommend that you use a current limiting resistor and
> > > put 10 or 20 or more in a string. This guarantees that every LED
> > > in that string will get the same current.
> > >
> > > For example, if you had 20 LEDs and each one had 1.7V
> > > forward voltage drop, you would have a total forward voltage
> > > drop of 34 volts. If you use a 36 VDC supply you can tweak the
> > > resistance
> > > to get the current you want. To get 20ma you would divide 2 volts
> > > by .02 A to get a resistance of 100 ohms. The 2 volts comes from
> > > subtracting 34V from 36V.
> > >
> > > This approach can be modified to match whatever power supply
> > > you have laying around to the LEDs you have.
> > >
> > > Gus
> > >
> > > On Feb 14, 2008, at 10:19 PM, javaguy11111 wrote:
> > >
> > > > I went ahead and placed an order for some as well.
> > > >
> > > > I am wondering if just doing simple current limiting
resistors is
> > > > sufficient or if a proper LED driver chip would be the better
> > way to
> > > > go. From what I have read, at least for visible LEDs, you
want to
> > > > match the current in the LEDs to ensure that they all shine
evenly.
> > >
> > > [Non-text portions of this message have been removed]
> > >
> > >
> > >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
> > Be sure to visit the group home and check for new Links, Files, and
> Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBs
> > Yahoo! Groups Links
> >
> >
> >
> >
there is such a thing as a free lunch pail ......
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