kopia lustrzana https://github.com/micropython/micropython
docs/library/pyb.ADC.rst: Document new features for ADCAll.
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@ -14,10 +14,12 @@ class ADC -- analog to digital conversion
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val = adc.read() # read an analog value
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val = adc.read() # read an analog value
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adc = pyb.ADCAll(resolution) # create an ADCAll object
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adc = pyb.ADCAll(resolution) # create an ADCAll object
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adc = pyb.ADCAll(resolution, mask) # create an ADCAll object for selected analog channels
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val = adc.read_channel(channel) # read the given channel
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val = adc.read_channel(channel) # read the given channel
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val = adc.read_core_temp() # read MCU temperature
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val = adc.read_core_temp() # read MCU temperature
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val = adc.read_core_vbat() # read MCU VBAT
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val = adc.read_core_vbat() # read MCU VBAT
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val = adc.read_core_vref() # read MCU VREF
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val = adc.read_core_vref() # read MCU VREF
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val = adc.read_vref() # read MCU supply voltage
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Constructors
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Constructors
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@ -81,27 +83,42 @@ The ADCAll Object
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.. only:: port_pyboard
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.. only:: port_pyboard
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Instantiating this changes all ADC pins to analog inputs. The raw MCU temperature,
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Instantiating this changes all masked ADC pins to analog inputs. The preprocessed MCU temperature,
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VREF and VBAT data can be accessed on ADC channels 16, 17 and 18 respectively.
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VREF and VBAT data can be accessed on ADC channels 16, 17 and 18 respectively.
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Appropriate scaling will need to be applied. The temperature sensor on the chip
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Appropriate scaling is handled according to reference voltage used (usually 3.3V).
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has poor absolute accuracy and is suitable only for detecting temperature changes.
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The temperature sensor on the chip is factory calibrated and allows to read the die temperature
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to +/- 1 degree centigrade. Although this sounds pretty accurate, don't forget that the MCU's internal
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temperature is measured. Depending on processing loads and I/O subsystems active the die temperature
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may easily be tens of degrees above ambient temperature. On the other hand a pyboard woken up after a
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long standby period will show correct ambient temperature within limits mentioned above.
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The ``ADCAll`` ``read_core_vbat()`` and ``read_core_vref()`` methods read
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The ``ADCAll`` ``read_core_vbat()``, ``read_vref()`` and ``read_core_vref()`` methods read
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the backup battery voltage and the (1.21V nominal) reference voltage using the
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the backup battery voltage, reference voltage and the (1.21V nominal) reference voltage using the
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3.3V supply as a reference. Assuming the ``ADCAll`` object has been Instantiated with
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actual supply as a reference. All results are floating point numbers giving direct voltage values.
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``adc = pyb.ADCAll(12)`` the 3.3V supply voltage may be calculated:
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``v33 = 3.3 * 1.21 / adc.read_core_vref()``
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``read_core_vbat()`` returns the voltage of the backup battery. This voltage is also adjusted according
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to the actual supply voltage. To avoid analog input overload the battery voltage is measured
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via a voltage divider and scaled according to the divider value. To prevent excessive loads
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to the backup battery, the voltage divider is only active during ADC conversion.
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If the 3.3V supply is correct the value of ``adc.read_core_vbat()`` will be
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``read_vref()`` is evaluated by measuring the internal voltage reference and backscale it using
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valid. If the supply voltage can drop below 3.3V, for example in in battery
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factory calibration value of the internal voltage reference. In most cases the reading would be close
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powered systems with a discharging battery, the regulator will fail to preserve
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to 3.3V. If the pyboard is operated from a battery, the supply voltage may drop to values below 3.3V.
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the 3.3V supply resulting in an incorrect reading. To produce a value which will
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The pyboard will still operate fine as long as the operating conditions are met. With proper settings
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remain valid under these circumstances use the following:
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of MCU clock, flash access speed and programming mode it is possible to run the pyboard down to
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2 V and still get useful ADC conversion.
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``vback = adc.read_core_vbat() * 1.21 / adc.read_core_vref()``
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It is very important to make sure analog input voltages never exceed actual supply voltage.
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It is possible to access these values without incurring the side effects of ``ADCAll``::
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Other analog input channels (0..15) will return unscaled integer values according to the selected
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precision.
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To avoid unwanted activation of analog inputs (channel 0..15) a second prarmeter can be specified.
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This parameter is a binary pattern where each requested analog input has the corresponding bit set.
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The default value is 0xffffffff which means all analog inputs are active. If just the internal
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channels (16..18) are required, the mask value should be 0x70000.
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It is possible to access channle 16..18 values without incurring the side effects of ``ADCAll``::
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def adcread(chan): # 16 temp 17 vbat 18 vref
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def adcread(chan): # 16 temp 17 vbat 18 vref
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assert chan >= 16 and chan <= 18, 'Invalid ADC channel'
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assert chan >= 16 and chan <= 18, 'Invalid ADC channel'
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@ -140,4 +157,5 @@ The ADCAll Object
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def temperature():
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def temperature():
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return 25 + 400 * (3.3 * adcread(16) / 4096 - 0.76)
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return 25 + 400 * (3.3 * adcread(16) / 4096 - 0.76)
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Note that this example is only valid for the F405 MCU and all values are not corrected by Vref and
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factory calibration data.
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