it might have been me who posted the CD4520 link, it was at the Analog Cottage, i just tried the URL - http://ourworld.compuserve.com/homepages/the_analog_cottage/diyelpro.htm but it wouldn't work, i also just searched Alta Vista, and that link wouldn't work either - it was last updated in April, so maybe it's just a temporary glitch
credit where credit is due and all that, so if it's still not working in a few days, does someone want to remind me and i'll convert the papers i have into a small text file (just have to get the scanner working...)