I'm gonna give the link to the VCO, then go to bed; it's now 5:00 am so it's past my nappy time.
The VCO circuit can be found here:
The siren ciruit is the one I use in the screwdriver but instead of gating it with a square wave, the circuit is modulated with a sine wave. At pin 9 and the other end to ground I use two large value parts that can be adjusted for personal taste such as 22Meg and 10uF or 15 Meg and 1 uF, etc. These parts determine how fast-- or how slow-- the screwdriver will sweep from one end of the frequency range to another. The frequency cap used is .001 uF so the VCO will work in the near ultrasound. I lost my notes so one will have to pop in resistor values to get it to work no higher than 20 kHz and probably less at 15 kHz upper limit. The screwdriver will however work extremely well at lower audible frequencies producing as much as 143 dB (but we always try for more) of sound, and this will make family & friends hate you as well as upset nearby neighbors so keep the frequencies above 12 kHz-- most humans can't hear that high anyways. But sound of such intensity can cause pain, headaches, and deafness with continued exposure even at ultrasound frequencies.
same as with the first part: the .001 cap on top of the 4046 but the frequncy resistor & cap are mounted in front. The 1K resistor that connects from pin 2 of the XR2206 to pin 9 of the CD4046 is wired below the two ICs on the bottom of the circuit board but make sure the wire is protected with tape or heat shrink tubing so the wires won't short any of the IC pins. That could ruin a lot of nice work very quickly. Still, feel free to experiment with the values; each screwdriver always needs some tweaking for proper operation.