dac

machine Module

Class DAC

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ESP32 has two 8-bit DAC (digital to analog converter) channels, connected to GPIO25 (Channel 1) and GPIO26 (Channel 2).
The DAC driver allows these channels to be set to arbitrary voltages.<br The DAC channels can also be driven with DMA-style written sample data, via the I2S driver when using the “built-in DAC mode”.

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This class includes full support for using ESP32 DAC peripheral.

ESP32 DAC output voltage range is 0-Vdd (3.3 V), the resolution is 8-bits

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Create the DAC instance object

dac = machine.DAC(pin)

pin argument defines the gpio which will will be used as dac output.
Only GPIOs 25 and 26 can be used as DAC outputs.
The pin argument can be given as pin number (integer) or the machine.Pin object.

>>> import machine
>>> dac=machine.DAC(25)
>>> dac
DAC(Pin(25), channel: 1)
>>> 

Methods

dac.deinit()

Deinitialize the dac object, free the pin used.

dac.write(value)

Set the DAC value. Valid range is: 0 - 255
The value of 255 sets the voltage on dac pin to 3.3 V

dac.waveform(freq, type [,duration=0] [,scale=0] [,offset=0] [,invert=2])

Generate the waveform on the dac output

Arg	Description
freq	the waveform frequency; valid range: 16-32000 Hz for sine wave 500-32000 Hz for noise 170 - 3600 Hz for triangle 170 - 7200 Hz for ramp and sawtooth
type	the waveform type, use one of the defined constants: SINE, TRIANGLE, RAMP, SAWTOOTH and NOISE
duration	optional, is given, waits for duration ms and stops the waveform
scale	optional, only valid for sine wave; range: 0-3; scale the output voltage by 2^scale
offset	optional, only valid for sine wave; range: 0-255; ofset the output voltage by offset value
invert	optional, only valid for sine wave; range: 0-3; invert the half-cycle of the sine wave

dac.beep(freq, duration [,scale=0])

Generate the sine wave beep on the dac output

Arg	Description
freq	fequency; valid range: 16-32000 Hz
duration	the duration of the beep in ms
scale	optional; range: 0-3; scale the output voltage by 2^scale

dac.write_timed(data, samplerate [,mode=machine.DAC.NORMAL] [,wait=False])

Output the values on dac pin from array or file using ESP32 I2S peripheral
The data in array or file must be 8-bit DAC values
The data from array or file obtained with machine.ADC.read_timed() can be used.

Arg	Description
data	array object or filename If an array object is given, write data from array object The array object can be array of type 'B', or bytearray If the filename is given, the datafrom the file will be output
samplerate	the sample rate at which the data will be output valid range: 5000 - 500000 Hz
mode	optional, default: machine.DAC.NORMAL; if set to machine.DAC.CIRCULAR the data from array or file will be repeated indefinitely (or until stopped)
wait	optional, default: False; if set to True waits for data output to finish

dac.write_buffer(data, freq [,mode=machine.DAC.NORMAL] [,wait=False])

Output the values on dac pin from an array using timer
The in the array must be 8-bit DAC values
The data from an array obtained with machine.ADC.collect() can be used.

Arg	Description
data	array object of type 'B'
freq	float; the frequency at which the data will be output valid range: 0.001 - 18000 Hz
mode	optional, default: machine.DAC.NORMAL; if set to machine.DAC.CIRCULAR the data from array will be repeated indefinitely (or until stopped). Some 'cliks' can be expected when playing continuously if the first value differs from the last one.
wait	optional, default: False; if set to True waits for data output to finish

dac.wavplay(wavfile, [,correct])

Plays the WAV file on dac pin
Only PCM, 8-bit mono WAV files with sample rate >= 22000 can be played

If the optional argument correct is given, the sample rate is corrected by correct factor.
The allowed range is: -8.0 - +8.0 (float values can be entered).

dac.stopwave()

Stops the background proces started by dac.waveform(), dac.write_timed() or dac.wavplay() function.

dac.freq()

Changes the frequency of the background waveform proces started by dac.waveform() function.