04.23.08
PCB Manufacture notes and PreAmpV0.2 Died!
Just for future reference (because I always forget), using the naff double sided PCB, 3:30 exposure was enough, but by far and away the most important point was to remember to jam the acetate down to the exposure unit, to the point of stressing the joints. Too many times have I relied on the foam in the lid of the exposure unit only to find that the acetate has warped slightly so I get a blurring after developing. Argh! Never again!
On the preamp front, it died! I dont know why, but I know what could have happened. Today in the lab, I came back from cleaning the “drop chamber”, as I like to call it, plugged it back in and it didnt work. I think it was because there was a DC spike on the output of the hydrophone which then knocked out the amplifier input. Here is my reasoning. I washed the hydrophone in hot water, boiling hot, since its the best way of getting rid of all the contaminants. I think this cause a charge build up in the peizoelectric material (either that or it was still hot, hence a wierd DC value) which then discharged (or stayed the same if it was simply due to the heat) and wiped out the input with a fair amount of voltage.
So next PCB, remember the protection diodes! I didnt put them on this time because I couldnt be bothered, and I didnt think this would happen!
p.s. Also, dont forget to place some text so you know which way round the acetate is supposed to go! Plus that the text that is to be on the bottom layer should be flipped! Elementary I know, but always forgotten!