161 lines
5.8 KiB
ReStructuredText
161 lines
5.8 KiB
ReStructuredText
Environmental Sensing Sample
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############################
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Overview
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========
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This sample implementes a simple environmental sensing service using the Arduino
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101 board.
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The sensor subsystem application collects temperature, humidity and pressure
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data from a set of sensors connected to the Arduino 101 and sends it to the SoC
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through IPM. The collected sensor data is also displayed by the sensor subsystem
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on a Grove LCD.
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The application processor exposes the received sensor data as a simple Bluetooth
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Environmental Sensing Service.
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Requirements
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============
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To use this sample, the following hardware is required:
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* Arduino 101
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* `Grove LCD module`_
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* `Grove Base Shield`_ [Optional]
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* `HDC1008 Sensor`_
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* `BME280 Sensor`_
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Wiring
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======
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External Wiring
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---------------
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The sample uses the HDC1008 sensor for temperature and humidity measurement, and
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the BMP280 sensor for pressure measurement. This section describes how to wire
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these sensors to the Arduino 101 board.
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Both sensors operate at 3.3V and use I2C to communicate with the Arduino. On the
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Arduino 101, the I2C data pin (SDA) is exposed as pin A4 (on the ANALOG IN
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header) and the I2C clock pin (SCL) as pin A5 (also on the ANALOG IN header).
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Since the Arduino 101 doesn't have internal pull-up resistors, these need to be
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added externally when connecting SCL and SDA to the sensors.
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In addition to connecting the ground (GND), 3.3V power (VDD and VDDIO) and I2C
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pins, both HDC1008 and BMP280 require some extra wiring.
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For HDC1008, connect the address pins (A0 and A1) to GND (this sets the device
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address to the default used by the app). Also connect the RDY pin of the sensor
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to the A1 pin (on ANALOG IN header) of the Arduino board. This is needed as the
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application configures data-ready interrupt on that pin (GPIO pin 3).
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For BMP280, connect the SDO pin to GND and the CSB pin to VDDIO, since the
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sensor needs to be setup to use I2C, and not SPI.
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.. image:: figures/wiring.png
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:width: 600px
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:align: center
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:alt: Wiring with Arduino 101
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Using board sensors
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-------------------
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If you do not want to use any external sensors, you can use the Arduino 101's
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internal BMI160 sensor to do just temperature readings. To do this, you need to
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modify the channel_info array from the sensor subsystem application to contain
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only BMI160's temperature channel, and also remove the humidity and pressure
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characteristic from the control application (running on the application
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processor).
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If you choose this approach and you also want to use the Grove LCD, then you
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also need to modify the sensor subsystem application to only display temperature
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on the LCD, as humidity and pressure values will not be available.
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Grove LCD
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---------
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Using the Grove LCD is optional and it can be disabled by removing the Grove
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configuration options from the arc/proj.conf file.
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The Grove LCD communicates with the sensor subsystem through the I2C bus. When
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connecting the Grove LCD to the Arduino 101, either directly (similar to sensor
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wiring) or through a Grove Base Shield, you need to make sure that the I2C SDA
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and SCL lines have pull-up resistors connected between GND and the 3.3V power
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source.
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Take note that even though SDA and SCL are connected to a 3.3V power source, the
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Grove LCD VDD line needs to be connected to the 5V power line, otherwise
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characters will not be displayed on the LCD (3.3V is enough to power just the
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backlight).
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Building and Running
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====================
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Building
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--------
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This sample builds two applications for both the sensor subsystem (arc) and the
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application processor (x86). The resulting images need to be flashed to the
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device either using JTAG (openocd) or DFU util (USB).
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Before using the environmental sensing sample, the Arduino 101 board needs to be
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flashed with the firmware for its nRF51 Bluetooth LE controller. To do this,
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follow the steps from:
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https://wiki.zephyrproject.org/view/Arduino_101#Bluetooth_firmware_for_the_Arduino_101
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The sample provide a single :file:`Makefile` that builds both images, simple run
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make in the top level directory of the application and flash either using JTAG
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or using DFU. (DFU is preferred).
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The sample can be found here: :file:`samples/environmental_sensing` in the
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Zephyr project tree.
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.. code-block:: console
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$ make
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$ make flash # for flashing with JTAG
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Running
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--------
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The ARC (Sensor Subsystem) program collects temperature, humidity and pressure
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data using the sensors API and sends it to the x86 core through an outbound
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IPM. The collected data is also displayed on a Grove LCD.
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The x86 program reads the sensor data from an inbound IPM and exposes it as
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GATT characteristics (temperature, humidity and pressure) through a simple
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Bluetooth Environmental Sensing Service. The values of these characteristics
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are updated every time a new message containing sensor data is received.
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An example of sensor data values that can be seen on the Grove LCD is
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illustrated in the image below.
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.. image:: figures/temp_sensing_4.png
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:width: 400px
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:align: center
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:alt: LCD Display
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The data exposed over Bluetooth using an Environmental Sensing Service can be
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tested with a BLE Scanner app. The image below is a screenshot of such an application.
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.. image:: figures/temp_sensing_5.png
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:width: 400px
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:align: center
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:alt: BLE Scanner Application
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The temperature value is 0xBA09 (little-endian) which is equal to 2490 in
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decimal. Since the Bluetooth specification states that temperature values are
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expressed with a resolution of 0.01 degrees Celsius, the value exposed over
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Bluetooth is the same as the one displayed on the Grove LCD (24.9 degrees
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Celsius).
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.. _HDC1008 Sensor: https://www.adafruit.com/product/2635
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.. _BME280 Sensor: https://www.adafruit.com/products/2652
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.. _Grove Base Shield: http://wiki.seeedstudio.com/wiki/Grove_-_Base_Shield
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.. _Grove LCD module: http://wiki.seeed.cc/Grove-LCD_RGB_Backlight/
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