Homebrew PCBs

See my "laptop drill press" in the photos section, and message 2057 in this group which describes it.

>As soon as it arrives, I will be trying a surplus Derma-Spec
> lamp ($6.95) that has a small 6" Blacklight BLB tube and
> 1-Min. timer in it. I ordered 2, and plan on modifying the 1
> min. timer circuit to suit the exposure time needed. Maybe
> this will offer a little more control of the exposure.
 
I did exactly that, and it works, sort of, but there were a few problems:

1.  There is a transistor in there that gets very hot.  Painting the heatsink black with a magic marker seemed to help some.

2.  The lamp is pretty small, so it may not work very well, or be slow if you want to expose something bigger than 2 inches wide.  It takes about 10 minutes to expose photosensitized boards from GC using this lamp from a distance of about 1 1/2 inches.

3.  I believe that the amount of light that is put out changes as the lamp warms up.  This may have been the cause of a different amount of exposure I seemed to have on a double sided board I made.  There is an exposure meter circuit in the (highly recommended!) book The Art of Electronics by Horowitz and Hill, that might help.

A better solution might be to get a black light from a toy shop or party supplies store, for maybe $20-$30.  I plan to try that next time I want to make a board.  Warming the lamp for 10 minutes before making exposures might help make the exposures more consistent.

Cheers,
- Jan, fellow poor man :-)



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