555 IC Project - 'Red Alert' Siren query.

[Aerodyne]

This thread has deviated rather but is following an interesting path. As far as LED PCB exposure units go, I designed and made one four or five years back and sent it for publication in EPE. It was accepted but never saw print. I still use it from time to time but sunlight is less trouble! I too used my laser printer (until it finally gave up the ghost) and I used the same method as I practiced with the students at school, printing at high density on plain paper then 'translucentising' the paper with a quick spray of WD40 (on the back, not the print side or runs occur). This made a very satisfactory and essentially cheap mask for PCBs.
I still use ferric Chloride. It is cheap and messy, so care is needed.
I have two Canon inkjet printers, both support transparencies. However they are getting old, like their owner!

Regards
Tony