The Bastl Instruments Kastle Synth V1 .5 is a modular Lo-Fi Synth in pocket size. As such, it is ideally suited for the entry into modular synthesis , but also extends the advanced modular system with unique functions. In two Attiny 85 chips it combines a complex oscillator, LFO and waveform generator . Unlike its predecessor, Kastl Synth version 1.5 has a USB port for power supply , a metal case , and a modified sound generation system that is still battery powered, so you can create digital lo-fi sounds, melodic and noisy, soft, hard and drony sounds on the go. The Mini Modular Synthesizer develops its full potential in connection with various modular devices.
The oscillator section of the Bastl Kastle Synth has three parameters : Pitch , timbre and waveshape . All are equipped with control voltage and three different synthesis modes. The modes available are Phase Distortion, Phase Modulation (FM) and Track & Hold Modulation. Each mode uses two oscillators. The Waveshape knob can also be used to adjust the pulse width of the square-wave output from the main oscillator. There is a main and rectangular output that can be used independently or in combination. In version 1.5 the oscillator section has been revised , so that the Kastl Synth 1.5 sounds much fatter than its predecessor.
The voltage controllable LFO has a triangle and rectangular output and a reset input. This section has also been revised in the new version and now sounds different. A rungler-inspired stepped waveform generator produces eight different voltages, either in random order or in eight- or 16-level repetitive patterns. Pattern loop playback depends on how BIT IN is patched.
The Kastle project by Bastl Instruments is an Open Source DIY project based on two Attiny 85 chips that can be reprogrammed with Arduino (google: "programming Attiny 85 with Arduino"). One chip is used to generate sounds, while the second chip is dedicated to modulation. For the Attiny Chips there are several firmwares available. Many of them can be found on the gitHub site;