In this Instructable, I'm going to provide a straight-forward schematic and some brief explanations as to how this will work and also some ideas as to what kind of tinkering you can do with this device.
Step 1: Components List
*This resistor can vary between 10k Ohm and 100 k Ohm but other pots (200k or 1M) sound really nice.
470 microFarad Polarized (I prefer something lower than 100 microFarads and I strongly suggest using a 50 microFarad capacitor).
0.01 microFarad non-Polarized)*
*This capacitor can vary between 0.01 microFarads and 0.27 microFarads. I noticed that using a 0.1 microFarad capacitor gets extremely close to a square wave.
8 Ohm Speaker
9 volt Battery
9 volt Connector
Potentiometer (for volume adjustment)
Step 2: Schematic
The LM386 has a built in feedback resistor (1350 K Ohms) to account for the likelihood that you will use a battery for your projects. By connecting Pin 1 and 8 together, you are bypassing this resistor.
Pin 7 doesn't connect anywhere.
Pin 6 connects to the 9 volt battery.
Pin 4 connects to the ground
As seen in the first picture, the Red X's indicate that there is no connection. So Pin 2 and 3 do not connect, and Pin 2 and 4 do not connect. The rest should be pretty straight forward.
The second picture is an earlier schematic. It is the same but has a few more notes. Rt and Ct indicate that these components can vary. By changing these components you can effect the Frequency being generated.
A simple equation (or so I heard) to determine the Frequency in Hertz is (2.5)/(Rt * Ct). Rt will be between 10,000 and 100,000 Ohms.
If R3 (100 Ohm) is left out or removed, you will get a loud squeal so try to avoid that.
Step 3: Things to Try
Replace Rt with a PhotoCell to create a Solar theramin type device.
Switch the 0.01 microFarad capacitor with anything between 0.27 microFarads.
I'm not sure about this but with a 470 microFarad capacitor, I get loud clicks/tapping sounds rather than a tone (maybe I just made a mistake). I fixed this by using much smaller capacitors. I noticed that anything bigger than 100 microFarads sounds like a purring cat but anything smaller sounds like a real tone.
Step 4: Conclusion
The great thing about this is that it doesn't drain the power of a 9 volt battery. With other projects, the 9 volt drained in a day.
Step 5: Square Wave
The schematic posted in the images should give you a square wave oscillation.