# Help oscillator BF

Good morning,
I need to make an oscillator that produces a variable frequency and in repetition from 1,000 to 30,000 Hz, square wave is fine, with 1 volt pp output to be applied to the input of an audio amplifier.
I thought of the NE555. Or do you have a more powerful solution?
Thank you.

Use one of the Analog Devices DDS modules, e.g. AD9850

thanks for the reply, but the module generates the repetition signal from 1000 to 30,000 Hz or not?
It is not clear.

From fractional Hz to 60MHz, IIRC, with about 30 steps per Hz.

It's not easy to get a square wave out of a 555, especially with variable frequency, but you can double the frequency and run the output through a type-T flip-flop which will make a square wave from the rectangle wave or pulse, and it cut the frequency in half.

Then, you'll need to run the output through a voltage divider (or pot) to knock-down the voltage and a capacitor to remove the DC component (to get a 1V "AC" square wave that goes from -.5V to +5V) . Audio amplifiers like to see an AC input... Most amplifiers have a capacitor on the input but it's smart to play-it-safe.

The biggest issue with a 555 may be knowing the frequency.

The Arduino's [u]tone()[/u] function can do it (again with the resistors & capacitor).

Or, you may be able to use your sound card with [u]Audacity[/u] or an audio generator application.

But soundcards are designed for audio, so 30kHz may be a problem, especially a 30kHz square wave. Audacity can generate sine or square wave tones up to the Nyquist limit (half the sample rate) so you can get above the audio range with a high sample rate (96kHz or 192kHz are standard) so digitally it's not an issue, it's just a question of the particular soundcard. (You need a higher sample rate for accurate square waves.) And the output voltage from a soundcard is "unknown" until you measure it.

Or, you can buy a little [u]Audio Generator[/u].

Or you could use an AD9850, which has both sine and square outputs, and is very cheap.

Or use two 555s. Connect the two capacitors together using a resistor and have one modulate the other. Take the output from the digital output of the faster one. It wonâ€™t be a square wave but it will be a rectangular one and there is little difference in the sound. If you really must have it square then put the output through a divide by two D-Type edge triggered flip flop with Q bar wired up to D and double the frequency of the fast 555.

You can also get the same effect with two uni-junction transistors, but they are hard to get these days.