Ligth intensity in my experience is only a problem on white solder mask, for evrething else, if in this case the proyector is too dim, you just expose a little bit longer:-) the test metodology is very simple
When i talk about a cnc , its because I think that the downscaling of the image should be enough to achive a dpi resolution that can match a photoploter resolution wich are about 2400 dpi for the lower range oneswicth enough resolution for pcb procesing. So you proyect a small squarean then the cnc performs a raster scann on the pcb.
Why do you bother with pcb registration? A few tooling pins should suffice
--- In Homebrew_PCBs@yahoogroups.com, Andrew Leech <coronasensei@...> wrote:
>
> I really like this idea myself. Could even try the route of a diy lcd
> projector:
> http://users.telenet.be/cool_things_with_fresnel_lenses/LCD_gettingstarted.htm
> for instance, just replace the projection lens with a perspex table and
> use a fresnel that images clearly onto it. The biggest problems would be
> the contrast of the blacks and the sharpness of the edges, but I can't
> help but think that if the image is clear and crisp on screen it could
> be clear on the pcb once it's reduced down from full screen to small
> enough pcb. But yeah, it's never going to be as accurate as a really
> good high res transparency, but if you just need a fairly simple pcb
> it'd be very quick to use.
>
> Certainly, a laser based pico projector could be even better, depending
> on minimum dot size / resolution. It would also depend on whether the
> blue laser is bright enough / high enough wavelength to expose the
> resist. just put a ruler in your image beside the pcb, and sit a real
> ruler beside your real pcb, and use that to get the right distance /
> projection size.
>
> With either of these techniques, you could show the pcb image dimly in
> red initially to line up the pcb, then switch it to blue/white full
> brightness to hopefully expose the resist.
>
> Sure, a cnc with a blue / uv laser could/should work even better, but it
> would probably be slower, possibly harder to align, and requires a cnc
> bed. As much as I would like one of them, I don't have one.
>
> Andrew
>
> On 9/01/2012 11:18 PM, psykhon@... wrote:
> > I Think its definitely doable but complex, the main obstacle will be finding the optics and necessary calculatons to proyect the 96dpi image onto the board with this image scaled down to get 600 or more dpi, from there the board could be moved in x and y in a raster way.
> > I think it would be a little bit easier to adapt a cnc to work as a laser raster scanner, see bungard, they are doing exactly this idea.
> >
> >
> >
> >
> > --- In Homebrew_PCBs@yahoogroups.com, "AlienRelics"<alienrelics@> wrote:
> >> A very high resolution projector or monitor would be 1280x1024, do you agree?
> >>
> >> Some here have tested Laser printers and found 600dpi models to be wanting, 1200dpi being de rigueur.
> >>
> >> So that is only about 2x1.5 at 600dpi, 1x0.8 at 1200dpi.
> >>
> >> A monitor is normally around 72dpi to 96dpi.
> >>
> >> A clever thought, however.
> >>
> >> Steve Greenfield AE7HD
> >>
> >>
> >> --- In Homebrew_PCBs@yahoogroups.com, Raj Jain<r.k.jain.or@> wrote:
> >>> I have watched the discussions on printers and their limitations on this
> >>> forum.
> >>> I have seen the use of DLP projectors to harden resin in 3D printers.
> >>> I was wondering if a similar adaption will be effective in exposing
> >>> photoresist material at very high resolutions.
> >>> Maybe use high resolution CRT or LCD monitor as a contrasting source of PCB
> >>> image. A PCB could be prepared and taped on the monitor for exposed.
> >>> ...raj
> >>>
> >>
>