Simplest option for generating audio tones?

Question

I'm looking for the simplest way to generate audio tones. Something like a square or sine wave, but I want multiple tone options. For example, two quick beeps, one at 440Hz, one at 1Khz. The tones should occur at the press of a button, and again at the release.

I am aware that a square wave can be generated with a 555 timer, but I don't know how to produce multiple tones. I also know a simple microcontroller can be used with a DAC, but I have a few requirements:

1. Parts count and cost as low as possible. Under $1 in higher quantities of components is ideal.
2. The components must not require FCC certification or SDoC, which is a concern going the microcontroller route.
3. The audio signal must be a mic-level signal.

Is some kind of MCU unavoidable in this situation? I've yet to find a suitable solution that covers all those bases, so any help is greatly appreciated!

Answer 1

This is one of the simpler ways:

Source: https://www.nutsvolts.com/magazine/article/op-amp-cookbook-part-3 Tone control could be done with mosfets switching components (like a parallel cap for C1\C2 (maybe you'd only need one?)

Op amps with the bandwidth you need can be had for the 10c cost range with quantity. Timing would need to be done with a 555 timer. This is probably not the best way, but "a way" to design a circuit like this

Answer 2

By far, the simplest physical implementation is to use an MCU. I would use something like the PIC10F200. The only external components would be a bypass capacitor for the power supply, plus a simple RC filter for the audio output.

^{simulate this circuit – Schematic created using CircuitLab}

The audio output on pin 4 would be a synthesized delta-sigma signal containing the tones, triggered by the changes on pin 3. R1, R2 and C2 attenuate the signal down to mV levels and provide a low-pass function with a 10 kHz cutoff frequency.