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Since the previous post did not upload the circuit, try this. You can use a 555 timer to make a square wave of the frequency you want. Put the output through a capacitor to a small loud speaker. Measure the ac voltage across the speaker. If it is less than the output from the 555 with the speaker removed, you can put a logic gate line driver or other type with higher current capacity (putting all six gates of a 4049 in parallel will also work.) output and then out of that go to the capacitor and speaker.