An optimized toy piano.
The pulses of the LFO (square wave) can be used as triggers for notes, with the knob the frequency is changed. The 3.5mm jacks are used as input for external trigger/gate signals, using the toggle switches to switch between input and internal frequency. The contacts made with the metal pins and clips determine the pitch of the notes played. The LEDs indicate each pulse, internal or external.
A toy car with additional functions:
Inputs for control voltage to trigger the sound samples, so the device can be played rhythmically with a sequencer.
The two knobs are used for sound control, a kind of gate function. They determine whether a sound is triggered and how long the "tone" is held.
A mono amplifier,
can be used as a preamp for microphones or as an amplifier of line signals to a loudspeaker.
An effect device with controls for overdrive and tone, similar to a distortion effect for guitars. Suitable for signals from the microphone, keyboard or audio from the smartphone.
Read more: Cornelia: Distortion/Filter Audio Effect with LM358