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General Category => Your projects => Topic started by: George on October 13, 2011, 20:21:53 PM

Title: Light Table [Box]
Post by: George on October 13, 2011, 20:21:53 PM
SO have you ever wanted a light box - you can always buy one - or - make a project
Anyway - I will be presenting my light box

Firstly I needed the basics - I got a pine wood pallet from a nearby business & cut it up
Title: Re: Light Table [Box]
Post by: kam on October 15, 2011, 14:37:35 PM
errrr... basic question: what is a "light box"?  :-\
Title: Re: Light Table [Box]
Post by: George on October 16, 2011, 01:02:59 AM
A lightbox is a unit for viewing photographic negatives or in our context aligning upper and lower pcb copies before UV exposure

refer to

http://www.dickblick.com/products/gagne-porta-trace-light-boxes-with-stainless-steel-frames/
Title: Re: Light Table [Box]
Post by: cheerio on October 16, 2011, 01:40:56 AM
Get a broken Flatscreen with your desired size, disassemble the panel and use the backlight of the display for your purpose.
Should be <30$.
Title: Re: Light Table [Box]
Post by: George on October 16, 2011, 03:51:59 AM
Great Idea - wish I'd seen it earlier - i've almost completed my lightbox now.
Details -
Screen is of opal acrylic 400mm x 300mm x 6mm
Case is pine ( from a pallet )
Back is "masonite" 4mm ( a hardwood panel creation )
Lamps - 3 x 10W fluorescents ~ 340mm long
Electronics for lamps - 3 x 11W compact flourescents ( cut the base away with a dremel )



Title: Re: Light Table [Box]
Post by: George on October 16, 2011, 04:33:16 AM
As an addition to cheerio's great idea here are some pics of a dissasembled flat panel LCD display

The fluorescent tubes are the tiny little tubes in the metal sleeve on one of the shots. The acrylic has a matt finish and a glossy reflective sheet behind it.

BUT be AWARE - generally the HV for the fluorescents is approx 1500-1800 Volts at startup & then cuts back to approx 900 Volts.
Title: Re: Light Table [Box]
Post by: kam on October 16, 2011, 10:00:50 AM
AHA! That is how it's called! I wanted to make one to check the PCBs for short-circuits or broken wires when i design with very thin and dense lines. This idea with the backlit is very good cheerio. I think i will be in the search for a bad tft...

George, one question. I have never managed to perfectly align the 2 transparent films of a 2 sided PCB. How can a lightbox be useful? And how do you align the PCBs? The best method i know so far is to align the 2 transparencies together, then cut them both exactly to the PCB outline and then use the outline to align each transparency to the PCb..
Title: Re: Light Table [Box]
Post by: George on October 16, 2011, 16:03:15 PM
Kam - for home made dual layer PCBs - the general method is align the two sides over each other on a lightbox - [ main reason i'm making one, apart from checking for holes & shorts ] - then tape the two transparencies together - one good idea  is to use a few drops of super glue to stick the transparencies together - approx 4cm away from the start of the pcb edge, then tie both together with some tape, you should be able to find some youtube examples.

Also lookup "edinborough etch" - by adding citric acid to FeCl you can make it more efficient, or replace FeCl with http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc/

btw -i've made my UV LED box from 16mm mdf, and bread boarded the electronics [sans UV LEDS], LEDs next , just have to work out my own way for some frosted acrylic - btw I'm using polycarbonate for that bit
Title: Re: Light Table [Box]
Post by: George on October 17, 2011, 15:05:58 PM
Current status of my lightbox

Fitted 3 x fluoros, with standard 90 degree twist mounts - have mounted these to a strip of pine - so if i choose to add another fluoro - - it won't take much work.
Also made the pine strips just the width of the fluoro mounts - so I can add a diffuser if i find the need.

Cut the compact fluoro bases all the way back - so i can remove the bayonette connectors & parallel the 3 units .

Ran the test fluoro unit (shown in a previous pic) for 6 hours - no problems - nothing heated up.

Just need to add a fuse ( also possibly a heat cutout fuse ( as this is a wood box )

Project minus's lots of work at the saw bench

Project Plus's Good Box - has some mass so it sits well on a table or bench, may even paint it!
Title: Re: Light Table [Box]
Post by: kam on October 17, 2011, 17:36:58 PM
what do you use for diffuser?