This is somewhat a living document. It may change if a certain requirement is discovered to be difficult to implement and fails a cost benefit analysis. The next step is to use it to generate a block diagram of the proposed system.
Preform additive synthesis with square waves.
Sum square waves of arbitrary magnitude and output the result as audio, a control voltage, and a visualization of the resulting waveform. The square waves frequencies are multiples of a fundamental frequency. If the fundamental frequency is 100 Hz, the other available frequencies will be [200, 300, …, 800] Hz.
The output fundamental frequency range will be decided during the design phase. As a minimum it should cover [0.1, 100] Hz for use as a LFO. Ideally it should go up to 10 kHz, in order to cover the useful audio range.
- Provide ability to be controlled by an external envelope generator. (Research if this is commonly done, or if a signal and its envelope are multiplied externally.)
- Provide ability to reset all harmonics to 0ᵒ phase via both push button and external control voltage.
- Provide ability to pause output waveform (probably by disconnecting the clock from the divider network) via both push button and external control voltage.
- Hopefully it can be powered by two 9 V batteries, stepped down to 5 V. If not, include a barrel jack and wall wart, with appropriate voltage conditioning circuitry.
- Provide ability for user to know if batteries are almost dead.
- Provide LED whose brightness changes with the output voltage amplitude. Useful for LFO applications.
Summary of Method
Generate an initial high frequency square wave and frequency divide it down to the desired harmonics. Sum the harmonics. Provide the ability to control the summing coefficients and invert individual harmonics to get a negative summing coefficient.
Currently I don’t know how to change the phase of each harmonic while still being able to optionally keep them in phase and at the correct multiples of each other (at least using analogue techniques).
- External clock signal
- A Reset control voltage
- A Pause control voltage
- The summed square waves: Audio (speaker), trs jack, bnc jack, tiny oscilloscope screen.
- A saturation warning light, which flashes if the summing circuit hits the voltage rail.
- A low power LED, which turns on when the batteries are almost dead.
- Each available harmonic needs a sliding pot to control the harmonic and a switch to control its polarity (adds 180ᵒ phase).
- Provide a switch to change between internal clock and externally provided clock.
- A Reset button, which resets all harmonics to 0ᵒ phase.
- A Pause button, which pauses the output waveform at its current value. When button is released the waveform resumes from where it was paused.