class DAC – digital to analog conversion¶
The DAC is used to output analog values (a specific voltage) on pin X5 or pin X6. The voltage will be between 0 and 3.3V.
This module will undergo changes to the API.
from pyb import DAC dac = DAC(1) # create DAC 1 on pin X5 dac.write(128) # write a value to the DAC (makes X5 1.65V) dac = DAC(1, bits=12) # use 12 bit resolution dac.write(4095) # output maximum value, 3.3V
To output a continuous sine-wave:
import math from pyb import DAC # create a buffer containing a sine-wave buf = bytearray(100) for i in range(len(buf)): buf[i] = 128 + int(127 * math.sin(2 * math.pi * i / len(buf))) # output the sine-wave at 400Hz dac = DAC(1) dac.write_timed(buf, 400 * len(buf), mode=DAC.CIRCULAR)
To output a continuous sine-wave at 12-bit resolution:
import math from array import array from pyb import DAC # create a buffer containing a sine-wave, using half-word samples buf = array('H', 2048 + int(2047 * math.sin(2 * math.pi * i / 128)) for i in range(128)) # output the sine-wave at 400Hz dac = DAC(1, bits=12) dac.write_timed(buf, 400 * len(buf), mode=DAC.CIRCULAR)
- class pyb.DAC(port, bits=8, *, buffering=None)¶
Construct a new DAC object.
portcan be a pin object, or an integer (1 or 2). DAC(1) is on pin X5 and DAC(2) is on pin X6.
bitsis an integer specifying the resolution, and can be 8 or 12. The maximum value for the write and write_timed methods will be 2**``bits``-1.
The buffering parameter selects the behaviour of the DAC op-amp output buffer, whose purpose is to reduce the output impedance. It can be
Noneto select the default (buffering enabled for
DAC.write_timed(), and disabled for
Falseto disable buffering completely, or
Trueto enable output buffering.
When buffering is enabled the DAC pin can drive loads down to 5KΩ. Otherwise it has an output impedance of 15KΩ maximum: consequently to achieve a 1% accuracy without buffering requires the applied load to be less than 1.5MΩ. Using the buffer incurs a penalty in accuracy, especially near the extremes of range.
- DAC.init(bits=8, *, buffering=None)¶
Reinitialise the DAC. bits can be 8 or 12. buffering can be
True; see above constructor for the meaning of this parameter.
De-initialise the DAC making its pin available for other uses.
Generate a pseudo-random noise signal. A new random sample is written to the DAC output at the given frequency.
Generate a triangle wave. The value on the DAC output changes at the given frequency and ramps through the full 12-bit range (up and down). Therefore the frequency of the repeating triangle wave itself is 8192 times smaller.
Direct access to the DAC output. The minimum value is 0. The maximum value is 2**``bits``-1, where
bitsis set when creating the DAC object or by using the
- DAC.write_timed(data, freq, *, mode=DAC.NORMAL)¶
Initiates a burst of RAM to DAC using a DMA transfer. The input data is treated as an array of bytes in 8-bit mode, and an array of unsigned half-words (array typecode ‘H’) in 12-bit mode.
freqcan be an integer specifying the frequency to write the DAC samples at, using Timer(6). Or it can be an already-initialised Timer object which is used to trigger the DAC sample. Valid timers are 2, 4, 5, 6, 7 and 8.
Example using both DACs at the same time:
dac1 = DAC(1) dac2 = DAC(2) dac1.write_timed(buf1, pyb.Timer(6, freq=100), mode=DAC.CIRCULAR) dac2.write_timed(buf2, pyb.Timer(7, freq=200), mode=DAC.CIRCULAR)
NORMAL mode does a single transmission of the waveform in the data buffer,
CIRCULAR mode does a transmission of the waveform in the data buffer, and wraps around to the start of the data buffer every time it reaches the end of the table.