Re: Google Groups
Welcome to Usenet (not Google Groups). This group is sci.electronics.design, which is actually older than Google.
It's entirely unmoderated and unrestricted, except for the generally accepted informal rules, known as *netiquette*.
Don't let Rob discourage you--c'mon and join the fun.
Re: NE566
The 566 is a really crappy oscillator. It's perfectly okay for a junkbox project, of course--I've done lots worse things myself--but for a real design there are many, much better choices nowadays.
On the simple end, the oscillator of a CD4046 will work as a very wide-range VCO with a pretty linear tuning characteristic over about
100:1 in frequency, though the center frequency isn't that accurately controlled by the RC time constant.The 4046 has only a square-wave output, so if that's a worry one could use one of many dual op amps. One section would be a Howland current source driving an integration capacitor with its other end grounded, and the other would be a Schmitt trigger controlling the polarity of the Howland. That will be better than the 556, but of course needs a lot of extra resistors. (On a PC board, one could make both the Howland and the Schmitt using one 8x resistor array, so it wouldn't be that many parts in real life.)
Cheers
Phil Hobbs