Some versions of this circuit charged up a capacitor (C1) with multiple pulses. This allowed the PIC to monitor the high voltage and produce a regulated output. Here is the current Source File and Hex File.
Since our setup only does single sided boards inhouse, a 'surface mount' layout was produced to accomodate thru-hole parts. For instance, the 8 pads for the PIC socket are spread to 0.5 inch to match the 'splayed out' leads from the socket.
In order to conserve power, a zener was used in place of the usual 5 volt regulator.
This allows doing extra tricks with the sleep mode for extended battery life.
Another variation uses a PIC12F683 with a switchable clock speed.
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