Anytime is a good time to move on to manufacturing one's own PCBs. As hard as it may be, I admit defeat in this aspect because all my attempts ended in frustration. The one I'm left with and I read many good things about is the UV curable etching mask method. I don't remember why I avoided this for so long. I must have been put off by the use of UV lamps, transparent sheets, careful timing, some new chemicals in carefully measured proportions and then the actual etching. Luckily the UV light can be produced much more efficiently and cheaply by LEDs and there are a handful of good DIY examples on the internet. The rest will be dealt with methodically, step-by-step.
Yet another UV box, you'll say, and you'd be right. However, I'm planning on doing something different this time. Something probably worth documenting. While all boxes I've seen were using an auxiliary power supply to produce 12V for groups of 3 LEDs, there's none powered directly from the power grid. The circuit is widely used nowadays in LED bulbs, Christmas lighting and such. I don't see why shouldn't this work.
Needless to say, that's a dangerous project involving high voltages. While most projects do, this one will have more dangerous areas that need to be isolated. In fact the entire back side of LED board will be hazardous. For extra-protection from the high voltage involved, the on/off LED switching will be handled by a single pole relay.
Warning:
This project involves HIGH VOLTAGE! Touching a high voltage live wire is DEADLY! Please take proper precautions if you are attempting to reproduce it.
I've ordered the LEDs and until they arrive I should come up with the box shape and components arrangement within it. Most definitely it will have double exposure capability. That means there will be an LED board on the bottom of the box and one on the lid. The electronics will have a separate closed compartment near the LCD display and the configuration buttons - that I didn't figure in the schematic above.
Meanwhile I invite you to read another Bogdan's post about a similar project. That's a nicely crafted box by the way!
Update: Check-out Part 2 - The high voltage electric circuit.