Sorry if this is a bit vague but I'm looking at building:
A filter unit which can be controlled automatically via an oscillator output. I'd like the oscillator to output square, sine, and sawtooth waves. I'd also like to be able to manually control the rate.
It sounds like you want to build an oscillator
(VCO), not a filter (VCF).
If you truly are interested in a VCF, I have put some notes together here:http://www.experimentalistsanonymous.com/ve3wwg/doku.php?id=steiner_vcf
I haven't built this yet, but I plan to. It has simulated ok in LTspice.
Is this acheivable with a 40106?
I've checked the archives section on this site but it all looks a bit scary!
The CD40106 has been bent by many folks to operate as an oscillator. But the difficult thing is controlling it reliably over a wide frequency range. Most folks want the control voltage CV to specify a specific note to come out of the VCO. Doing so accurately is tricky. I have some notes here about the VCO that I recently built, but it is not the best project for the faint of heart:http://www.experimentalistsanonymous.com/ve3wwg/doku.php?id=synth_vco
If the frequency is low for a LFO (low frequency oscillator), then pitch control is not an issue and many circuits can be bent into use for that. I haven't gone there yet, so don't have much to say on that.
Hope that helps.