At first, i taught a simple circuit will do the job. I'm far from be an expert in electronics and i was wrong.
The unit will cost about nothing 'cause the part are cheap, but you are right, i will put it on a board.
Luckily, i have everything by hand, 'cause there is an electronic dep where i work.
My goal was to made something simple that everybody can do. I failed at it. Cant be so simple and work as safe as i wanted to.