Re: Loud Piezo Buzzer for Timer


RobZ wrote:
Hi all,
as the result of a dare, I am trying to build a shooting Timer. ( a
timer that responds to the sound of a firearm being fired and records
the times thereof).

The timing is done by an ATMEL micro.
the Start signal (from the Atmel) is a .5sec pulse.
I have been using this to switch on a transitor to connect the 9V
battery directy to the Piezo buzzer.
this works fine except the volume/db of the buzzer is far to low. the
Buzzer is rated 85Db with a supply voltage of 24V,
another problem is that a buzzer of less than .25 Sec is too quick
can any one assist in pointing me in the right direction re the
following:
a) Will a voltage doubler circuit (diode/capacitor network) work in
this instance?
b) must this "increased voltage" be stored in a capacitor before being
able to be used ?
c) if so, how do i connect it up to "release" the stored voltage -
similiar to flash trigger , connecting to ground?
d) given a 9v supply and a 5v trigger, could someone supply me a rough
schematic ?
e) the circuits i have been looking at (via google) typically use a 555
as an oscilator but they produce 200-300Volts!
am i on the right track here?
any Response is appreciated

Hi, Rob. One at a time:

a) Using a 555 as a voltage doubler will pump your 9V battery supply
up to 18V, It should definitely work to increase your piezo beeper
volume.

b) Any voltage doubler uses an output cap to store the energy. The
bigger the output cap, the more energy is stored. Your piezo isn't a
high current load (probably less than 20mA DC), though, so an enormous
storage cap shouldn't be much of a consideration.

c-e) The basic 555 voltage doubler circuit is at this link:

http://www.reconnsworld.com/power_voltdoubler.html

It should work exactly as shown in the link (555 driving 1N4002s and
220uF caps). Your hookup diagram should look soomething like this
(view in fixed font or M$ Notepad):

|
| BZ1
| |.-.| +18V
| || || |
| .-|| ||---'
| | || ||
| | |'-'|
| |
| From ___ |/
| uC >-|___|-o-| 2N3904
| 2.2K | |>
| .-. |
| 2.2K| | |
| | | ===
| '-' GND
| |
| ===
| GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

With the higher voltage and full voltage turn on, your beeper should
start up right away -- .25 seconds is plenty long for the beeper's
internal oscillator to start up and give you a good tone.

I hope this has been of use. Feel free to post again with more
questions.

Good luck
Chris

.

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