This is an analog square-wave generator with high and low pitch modes (selectable with toggle switch). This little runt packs eight tiny keys, volume, frequency range control and a mint green LED that shines bright green.
Built into an old metal case it is quite small, only about 2.5 inches wide. Powered by a 9v battery. Output is a standard 1/4 inch jack.
The square-wave produced gives you that classic lofi sound. It is monophonic and will play the highest key that is being pressed. The frequency range control adjusts the spread of pitches across the 8 keys.