FunctionGenerator

Arduino library to generate (numeric) wave forms for a DAC

Description

This library presents a class for a function generator in software. It is typical used to control one or more DAC's. To maximize signal quality one has to apply all (or most) processor power to calculate new values over and over again to get enough resolution. In practice the generator is useful for low frequencies, 0.01 - 25 Hz, depending on waveform and processor and number of DAC's. (see indication below).

Note: this class generates float values, performance wise this can be optimized, to achieve higher speeds at cost of accuracy / precision.

Performance

Indication of what performance can be expected (based upon 0.2.1 version).
Note that the values need to be transported to a DAC or serial port too.
Numbers based on performance example, for one single signal.

Processor	Clock	Waveform	usec/calls	max freq
Arduino UNO	16 MHz	sawtooth	62	60 Hz
Arduino UNO	16 MHz	triangle	74	50 Hz
Arduino UNO	16 MHz	square	53	1000 Hz
Arduino UNO	16 MHz	sinus	164	25 Hz
Arduino UNO	16 MHz	stair	81	50 Hz
Arduino UNO	16 MHz	random	37	1000 Hz

ESP32	240 MHz	sawtooth	3.8	1000 Hz
ESP32	240 MHz	triangle	3.9	1000 Hz
ESP32	240 MHz	square	2.8	1000 Hz
ESP32	240 MHz	sinus	13.6	250 Hz
ESP32	240 MHz	stair	4.8	800 Hz
ESP32	240 MHz	random	1.3	1000 Hz

assumption minimal 250 samples per period to get a smooth signal. if a rougher signal is OK, higher frequencies are possible.
ESP32 can do more calculations however 1000 Hz seems to be a nice upper limit for a software based function generator.
if one wants to control multiple DAC's one need to divide the numbers.

Note: hardware function generator https://github.com/RobTillaart/AD985X

Interface

Constructor

funcgen(float period = 1.0, float amplitude = 1.0, float phase = 0.0, float yShift = 0.0) All parameters can be set in the constructor but also later in configuration.

Configuration

void setPeriod(float period = 1.0) set the period of the wave in seconds.
float getPeriod() returns the set period.
void setFrequency(float frequency = 1.0) set the frequency of the wave in Hertz (1/s).
float getFrequency() returns the set frequency.
void setAmplitude(float amplitude = 1.0) sets the amplitude of the wave. TODO point to point? Setting the amplitude to 0 gives ?what?
float getAmplitude() returns the set amplitude.
void setPhase(float phase = 0.0) shifts the phase of the wave. Will only be noticeable when compared with other waves.
float getPhase() returns the set phase.
void setYShift(float yShift = 0.0) sets an Y-shift in amplitude, allows to set some zero point.
float getYShift() returns the set Y-shift.

Wave forms

t is time in seconds

float sawtooth(float t, uint8_t mode = 0) mode == 0 (default) ==> sawtooth /|. mode == 1 ==> sawtooth |.
float triangle(float t) triangle form, duty cycle 50%.
float square(float t) square wave with duty cycle 50%.
float sinus(float t) sinus wave, has no duty cycle.
float stair(float t, uint16_t steps = 8, uint8_t mode = 0) mode = 0 ==> steps up, mode = 1 steps down.
float random() noise generation.
float line() constant voltage line
float zero() constant zero.

Line() and zero() are functions that can be used to drive a constant voltage from a DAC and can be used to calibrate the generator / DAC combination.

Operational

See examples.

Future

waveforms

square duty-cycle (will be slower!)
triangle duty-cycle (makes sawtooth a special triangle)
trapezium wave (would merge square and triangle and sawtooth)

investigate

duty-cycle for sinus what does it mean. move peak.
white noise, pink noise etc.
investigate algorithms for performance gains (DAC specific values 10-12-16 bit)
Amplitude modulation ?
external clock to synchronize two or more sw function generators.
RC function curve.
heartbeat curve?
record a signal and play back

misc

stand-alone functions in separate .h?
mapping to voltage function.
check for synergy with https://github.com/RobTillaart/AD985X

examples

example ESP32 version as separate task...
example with DAC. 8 12 16 bit.
example with potentiometers for 4 parameters

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