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diff --git a/source/adc.rst b/source/adc.rst deleted file mode 100644 index 937b178..0000000 --- a/source/adc.rst +++ /dev/null @@ -1,104 +0,0 @@ -.. _adc: - -===== - ADC -===== - -Analog to digital conversion is the process of reading a physical -voltage as a number. Maple can convert voltages between 0 and 3.3V to -numbers between 0 and 4095. - -.. contents:: Contents - :local: - -ADC On Maple ------------- - -Doing analog-to-digital conversion on the Maple is simple. -:ref:`Maple IDE <ide>` contains a basic example. To see it, choose -Analog > AnalogInSerial from the :ref:`examples menu <ide-examples>`. - -In order to set up your board for conversion, first connect the wire -(potentiometer, etc.) with the voltage you want to measure to a -:ref:`pin <gpio>` which can perform ADC. Each pin which can do ADC -has "AIN" (or "ain") written next to the the pin number. Then, as in -the example program, set the chosen pin's :ref:`pin mode -<lang-pinmode>` to ``INPUT_ANALOG`` by calling ``pinMode(<your_pin>, -INPUT_ANALOG)``. You will usually do this in your :ref:`lang-setup` -function. Now you can use :ref:`lang-analogread` to perform an ADC -reading. - -.. _adc-function-reference: - -Function Reference ------------------- - -* :ref:`lang-analogread` -* :ref:`lang-pinmode` -* :ref:`libmaple-adc` (low-level ADC support) - -.. _adc-noise-bias: - -Noise and Bias --------------- - -Maple has a large number of pins which are capable of taking 12-bit -ADC measurements, which means that voltages from 0 to 3.3V are read as -numbers from 0 to 4095. In theory, this means that a change in -voltage of about 1 millivolt should change the numeric voltage reading -by 1. In reality, however, a number of issues introduce noise and -bias into this reading, and a number of techniques must be used to get -good precision and accuracy. - -In order to allow for good readings, LeafLabs has tried to isolate at -least some of each board's ADC pins and traces from strong noise -sources. However, there are always trade-offs between noise, -additional functionality, cost, and package size. More information on -these isolated pins is available in each board's hardware -documentation: - -* :ref:`Maple <maple-adc-bank>` -* :ref:`Maple RET6 Edition <maple-ret6-adc-bank>` -* :ref:`Maple Mini <maple-mini-adc-bank>` -* :ref:`Maple Native Beta <maple-native-b-adc-bank>` - -That said, there are a number of more general things you can do to try -to get good readings. If your input voltage changes relatively -slowly, a number of samples can be taken in succession and averaged -together, or the same voltage can even be sampled by multiple ADC pins -at the same time. - -Another important factor when taking a voltage reading is the -reference voltages that the sample is being compared against. For -Maple, the high reference is |vdda| and the low reference is ground. -This means that noise or fluctuations on either |vdda| or ground will -affect the measurement. It also means that the voltage you are trying -to sample must be between ground and 3.3 V. - -.. _adc-range: - -In the case of a variable reading, it is best if the voltage varies -over the entire range of 0 through 3.3 V; otherwise, only a fraction -of the sensitivity is being used. Some basic tools to accomplish this -are `resistor dividers -<http://en.wikipedia.org/wiki/Voltage_divider>`_ and `Zener diodes -<http://en.wikipedia.org/wiki/Zener_diode>`_\ -. However, `operational amplifiers -<http://en.wikipedia.org/wiki/Operational_amplifier>`_ and other -powered components can also be used if greater precision is required. - -.. _adc-recommended-reading: - -Recommended Reading -------------------- - -* `Wikipedia: Analog-to-Digital Converter - <http://en.wikipedia.org/wiki/Analog-to-digital_converter>`_ -* `Arduino Analog Input Tutorial - <http://arduino.cc/en/Tutorial/AnalogInputPins>`_ -* ST documentation: - - * `Application Note on ADC Modes - <http://www.st.com/stonline/products/literature/an/16840.pdf>`_ (PDF) - * `Application Note on ADC Oversampling - <http://www.st.com/stonline/products/literature/an/14183.pdf>`_ (PDF) |