For anyone who is interested in the basic theory, including a bunch of control circuits Maxim has an outstanding tutorial here: http://dbserv.maxim-ic.com/tarticle/view_article.cfm?article_id=93 Personally I find all of the control schemes listed much more complicated than the self induced VCO design we have discussed here. BAJ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads