Original cheap transformerless UV-LEDs bromograph PIC12F509

Preface

Fig.1 - The UV-LEDs bromograph during the exposure

Fig.1 – The UV-LEDs bromograph

A bromograph (or UV Exposure Unit, or UV Screen Exposure System) is a fundamental instrument for making PCBs using the photo-etching method. Unfortunately its price is usually prohibitive for a normal DIY maker and the UV-neons are expensive anyway if you’re thinking of building one.

I thought that UV-LEDs could represent a valid alternative to them and I made some experiments to test their effectiveness. Encouraged by the first positive results, I considered that even using UV-LEDs with a wide view angle, such as 120°, I would need 54 LEDs to light uniformly a surface of a common 160×100 mm board. That means at least 1A of current consumption or doubling in case of a dual-layer bromograph, plus, a small amount consumed by a timer circuit which I planned to include in the project. So, I decided to avoid the use of a transformer that is quite cumbersome and expensive. I surfed on the internet looking for a solution and I stumbled on Wutel‘s website. There, I found some circuits that, by exploiting the capacitive reactance, supply LEDs directly from the 220V.

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