Other stuff

25/6/09
I like to take a schematic from wherever and draw it up into a PCB and project file. It’s almost my favourite part of electronics and somewhat like doing puzzles. To these ends I’ve in the past carried on and made complete stuff I’m not really interested in so now I just finish up the project file then file it for the future. When I went on DIY stompboxes with my version of a ducker a guy who works for Paia, a kitset seller of some repute, mentioned a Paia ducker I searched out the schematic (as most of the Paia schematics are published somewhere) and drew up a PCB. I do this over my morning coffee to wake up.
The Paia ducker is interesting for me because, like most Paia stuff, it uses the designers own special way of solving problems, and in this case uses IC’s I’ve either never seen before or uses them in ways I’ve never used them.

The 555 I’ve used as an oscillator in astable mode but I’ve never used them in one shot or monostable mode as it is here and it had me wondering why pins 7 and 6 were tied together and pin 2 was the input until I got my 555 book out and realised it was set up in monostable mode. This means the key in signal is held open for the duration set by the hold pot. I think. I’m not sure but it looks something like that and the threshold determines when that happens. Then it feeds the LM339 which is a quad comparator chip and I really have no idea what a comparator is except that it obviously compares things… then makes a choice.
The IC’s and other paraphenalia to make this board would give me change outta 10 bucks but the outer world hardware of four pots, a rotary switch, and five inputs and a DC input would cost me about about 25-30 bucks and right now I’m both too busy not doing stuff I should be doing plus I’m outta cash so this one, though I’d love to have one by Monday for my upcoming slot at Vit S… it ain’t gonna happen.