Homebrew PCBs

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@...>
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]
 >
 >
 >

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