circuitpython/docs/library/pyb.DAC.rst

.. _pyb.DAC:

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.*

Example usage::

    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)

Constructors
------------

.. class:: pyb.DAC(port, bits=8)

   Construct a new DAC object.

   ``port`` can be a pin object, or an integer (1 or 2).
   DAC(1) is on pin X5 and DAC(2) is on pin X6.

   ``bits`` is 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.

Methods
-------

.. method:: dac.init(bits=8)

   Reinitialise the DAC.  ``bits`` can be 8 or 12.

.. method:: dac.noise(freq)

   Generate a pseudo-random noise signal.  A new random sample is written
   to the DAC output at the given frequency.

.. method:: dac.triangle(freq)

   Generate a triangle wave.  The value on the DAC output changes at
   the given frequency, and the frequence of the repeating triangle wave
   itself is 2048 times smaller.

.. method:: dac.write(value)

   Direct access to the DAC output.  The minimum value is 0.  The maximum
   value is 2\*\*``bits``-1, where ``bits`` is set when creating the DAC
   object or by using the ``init`` method.

.. method:: 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.

   ``freq`` can 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.

   ``mode`` can be ``DAC.NORMAL`` or ``DAC.CIRCULAR``.

   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)