Re: Some simple design help?

"Arfa Daily" <arfa.daily@xxxxxxxxxxxx> wrote:

>If the drive to the sounder is being driven with a pulsed square wave -
>which it almost certainly is - I would suggest that if you got a scope on
>it, you would see that it was actually going from 3v to virtually ground.

Yep - I did something like this last night. I suppose I
should have known the meter couldn't respond.

>You could glue a little AC coupled peak rectifier circuit on the end.
>Connect the + lead of a capacitor C1 of say 10uF, to the ' bottom ' end of the
>buzzer, and then connect the - lead to the cathode of a small signal diode D1
>ie 1N4148. Connect the anode of the diode to watch ground. Now connect the
>anode of another similar diode D2 to the cathode / cap junction, and finally,
>connect the + lead of another capacitor C2 of say 47uF to the cathode of the
>second diode. The - lead of this cap goes again to watch ground.

I drew this circuit out, but I'm not quite sure of the
function of D1 and C1 (see labels above) My simple design
just used the equivalent of D2 and C2, connecting the anode
of D2 to the positive end of the buzzer (B+) and the
negative end of C2 to the negative end of the buzzer (being
switched low). The watch is battery operated and floats
relative to the transistor in the device being switched, so
D2 just charges C2 when the buzzer is being sounded - which
switches the transistor. That's the way the timer was set
up in my first attempt.

Thanks for your comments.
.

Relevant Pages

  • Re: Some simple design help?
    ... >>You could glue a little AC coupled peak rectifier circuit on the end. ... >>buzzer, and then connect the - lead to the cathode of a small signal diode ... Connect the anode of the diode to watch ground. ... The - lead of this cap goes again to watch ground. ...
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