I'd like to buy or build a UV exposure unit for the photoresist method of making my own PCBs.
- adjustable timer knob
- works for double-sided PCBs
- US$50 budget
What are my options?
Making one for $50 with those features is going to be difficult. Here is my very simple one:
It's made from MDF and some strips of wood, held together with some glue and wood screws. A sheet of ordinary window glass rests on the upper wood strips.
I used standard 12" fluorescent light fittings, disassembled, with the tubes replaced by UV tubes. They are connected to a piece of mains cable and a mains plug.
I time the exposure (11 minutes) with the kitchen timer on my Dell Streak tablet. Although it's very crude, I get excellent results - 8/8 mil tracks if necessary - with transparencies printed on my cheap inkjet printer.
It cost me the equivalent of about $40.
You could build a basic unit like mine, and add the bells and whistles later.
Some members of the Homebrew PCB Yahoo group are using UV LEDs, but they are far more expensive than a couple of UV tubes. Enough LEDs for a small board could cost over $100, IIRC.