"Shaun" wrote in message
...

"Shaun" wrote in message
...
Hello,

I wanted to resurrect an old project from Popular Electronics magazine
May
1991. I thought some people on this list might want to build it.

Its a very very loud alarm, to get someone's attention, but the
frequencies
that it operates at don't match the description in the magazine article,
they're higher. The alarm is still very annoying though. Some of the
parts
are not available such as the matsu****a transducer ( piezo) if anyone
knows
were to get them please post. I use a piezo tweeter which is much larger
but works very well.

It's a three page article so here we go.

Shaun




I figured out how to get the frequencies right. Change C3 and C4 to
0.022uF
from 0.01uF
That lowers the frequencies and make the alarm louder and at the right
pitch. Problem solved.

Shaun


Other changes for more power and louder:

Change the 10 ohm resistor (R7) at the emitter of Q1 to a 3.3 ohms at 1
watt.
Change R6 to 180 ohms.
Change R5 to 470 ohms.
And for the piezo buzzer, use a piezo tweeter, you can get them off of ebay.

Shaun