This circuit generates frequencies determined by R3 and C1. We found it in the Radio Electronics magazine of May 1988. The power supply must be symmetrical.
The values of the capacitance between output A and ground can be programmed digitally in 18 steps...
This is one of many twin-T oscillator configurations that can be found in this section and on this...
This useful power supply was found in an 1985 Italian publication, but can still be assembled...