The square-wave gives you that classic lofi sound. It's played with a larger knob which controls the frequency. Hitting A has the knob work from a low to high pitch and B is the reverse. Pressing both merges this into one frequency that causes the knob to play from high to low and back to high which gives you a bit of flexibility.

Where start was is now the on/off toggle and select is now a red led. Power and signal are connected through the original wire to a breakout box containing a 9v battery for power and standard 1/4 inch jack.

Seven of these have been built.