Need help sweeping tone generator..

[epraizer]

I need help in designing a tone generator that sweeps at a frequency of 100Hz to 3kHz in a span of two seconds. It is powered by a 12 volts source and is enabled by an external trigger. The external trigger enables the tone generation when is at least 6 volts; otherwise no tone is generated. An 8-ohm speaker is used to produce the sound.

So far this is what I am able to come up with.

**broken link removed**

There is already external trigger.
The only problem left is the frequency sweep of 100Hz to 3kHz in a span of 2 seconds.
Thank you in advance.

 

[Hero999]

How will that produce a sweeping tone?

It will produce a single tone for about two seconds - it'll sound like beep.

 

[epraizer]

That is actually my problem. I need to make it sweep from 100Hz to 3000Hz in a span of 2 seconds.

 

[Hero999]

Connect the control voltage on the astable to the capacitor on the monostable via an inverting amplifier with a gain of 1, biased at half the supply voltage.

If you use a 556 timer and a dual op-amp you should be able to cut the IC count to two.

 

[epraizer]

Thanks for that. I'll try that out.

 

[audioguru]

The 555 will blow up if it tries to drive an 8 ohm speaker from a 12V supply. Its peak output current will try to be 1.2A. You must use a 39 ohm resistor in series with the speaker to limit the current to 200mA. Then the speaker will not be very loud because the 555 is not a power amplifier.

The output of a 555 is a square-wave buzz, not a sine-wave tone.

 

[Hero999]

Not quite, the 555 typically drops 2.5V with an output current of 200mA so the peak output voltage will be 3.5V, as it's AC coupled, but you're right the current will still be too high and will blow the 555.

Using a 64R speaker, adding a 39R resistor or reducing the supply voltage to 6V should solve the problem.

 

[audioguru]

The output of the 555 is almost 0V when at rest then it tries to go up to +9.5V before the capacitor charges to about 3.5V. 9.5V/8 ohms= 1.2A.

 

[Hero999]

I think it's unlikely that a single 1.2A surge is going to kill the 555.

Anyway who cares? The continuous current is still too high with the 8R speaker.