PIC Analogue Synthesizer

A real analog synthesizer to build using easy to get components, capable of a wide range of sounds. The two oscillators can be detuned for that classic synth sound. Dual oscillator mono synth. Really easy to build using just 1 custom programmed PIC chip, 4 ICs and single 12v supply. All circuits built on veroboard - no printed circuit board making skills needed. PIC based dual oscillator and digital keyboard scan. Analog VCF/VCA/Envelope. Waveforms : sawtooth, square (with pulse width adjust), triangle. Fully adjustable detune. Cool Arpeggiator. Portamento. Expandable, first two modules shown below. NEW Option of third oscillator with Pulse Width Modulation. Total cost estimate $89
PIC Analogue Synthesizer - schematic

PIC board, showing 18 pin PIC microcontroller and keyboard decoder.The PIC produces three outputs: two are oscillator outputs, either in-tune or detuned. The other is a trigger output for triggering envelope. The PIC scans the keyboard via 74HC154 decoder using top key priority. The PIC is programmed in assembler for speed and accuracy necessary for producing two oscillators in tune - the chip needs to run at 20 Mhz. The PDF file contains detailed of how I wired up salvaged Hohner keyboard to the 74HC154. Back of oscillator panel showing waveshape circuit. The dual waveshape circuit divides the PIC square wave into lower octaves (selectable range) and at the same time converts the square wave into an approximation of sawtooth (stairstep). The stairstep is fed into a comparator to produce a pulse width adjustable square wave. The square wave is also integrated to produce triangle. All waveshapes are selectable for each oscillator. Interesting effects can be obtained by mixing different waveforms produced by the two oscillators. If you listen to detunedsaw.wav you should be able to hear the beat of the two oscillators in detune 1 position. Voltage controlled filter, VCA, Envelope and Output Amp - using a single LM324 Quad op-amp and 4 transistors. The voltage controlled filter cutoff frequency is controlled either manually or follows AD envelope shape. The AD envelope feeds VCA. Finally a x2 output amp boosts the signal...

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