Buzzer/555 chip

[You2me]

I'm trying to connect a buzzer to my collision avoidance system that will beep when the car is within certain ranges from an object. I'm sending a PWM signal to the buzzer through a 555 chip but I'm getting weird results. I know this is probably more a 555 issue than a basic stamp one but maybe someone can help. The datasheet (www.national.com/pf/LM/LM555.html (http://www.national.com/pf/LM/LM555.html)) shows many different circuits I can build but I have no idea which one will help the most. I only need two different frequencies and they need to be loud enough to be heard over the motors. Thanks.

[PJ Allen]

The astable multivibrator is the basic free-running oscillator.· Two different frequencies is a two-tone oscillator, easy enough with a 555.· An oscillator enabled by an external signal (e.g. a Stamp pin output) is gated.

Update -- A "buzzer" will buzz on its own, but a "piezo speaker" requires a tone/frequency source.

[C.Moher]

Hook your buzzer up to a DC source...does it buzz ? If so, you don't need a frequency source, you have bought a buzzer by mistake. They just give you a single frequency beep when they get the right amount of DC. You need a piezo electric transducer or a small speaker.

If it doesn't buzz, hook it up one lead to P0, the other to the -ve rail and use this code:

FREQOUT 0, 2000, 3800
If it buzzes now, it begs the question as to why you are using a 555 timer to begin with when the Stamp can handle this far better.