Pulse doubler schematic

[jdzura at csc.com]

Tom,Bruce
<snip>
Do you think the pll will work well down to frequencies of
0 Hz when the car is not moving?  I don't think I've seen
one with a lock range the low.
A minor mod to your 30Hz Vats bypass circuit, to up the
frequency might work well with the frequency doubler.
You're correct, the PLL won't support a 0 Hz input, at least I don't think it
will. Although it is possible to design the lock in and track range to be very
wide, I don't know what the extremes are.
It may be that the digital design with a non"canned"  oscillator would be
suitable. There are some 32 KHz crystals available and that could be divided down
to the 100-200 Hz range fairly easily. My problem is that I don't like RC
oscillators when exposed to temperature extremes.
Maybe the guy with the PIC should just take care of the issue. It would seem that
the PIC would be a simple circuit to build, and very easy to implement.
What do you guys think?
Joe D