"Arfa Daily" wrote:

It's a slightly unconventional way of doing it, but if it works for your
application, then that's fine.

I really appreciate the help.

My way of doing it kept all the grounds
together - the watch and the external circuit, but ensured that the two
circuits were isolated from each other, and the correct polarity of drive
signal was always produced at the highest level, irrespective of the duty
cycle of the drive waveform. C1 AC couples the high frequency drive, which
is then floating with respect to ground. D1 then behaves as a basic shunt
rectifier, reclamping the voltage pulses about 0.6v above ground. D2 and C2
then form a charge pump to largely remove the low frequency pulsing of the
high frequency drive ie the reason that the buzzer goes BEEP BEEP BEEP.

Buzz '-' ------| |-------||----------^^^^-------- Drive to transistor
C1 | D2 |
-- --
D1 ^ -- C2
| |
------------------------------------------------ Gnd

Don't know if that will come out ok. Gives you the idea if it does.

Thanks for taking the time to draw it out. I drew it based
on your last message, and it appears I drew it correctly.
Let's see if I understand. "Buzz" is normally high, but
switches to and from watch ground (or near it) during
buzzing. When Buzz is high (off), D1 and D2 will be not
conducting and C1 will be charged. C2 will be discharged.

As Buzz goes low, D1 clamps at 0.6 volts and C1 discharges.
As Buzz then goes high D2 charges C2 through C1 and D1 is
reverse biased. If I get that right, then I see the
advantage of your design, in keeping the common ground (that
did worry me). Thanks again.