IoT Platform

Lynxari MPU9250 sensor device driver

This device driver is specifically designed to be used with the Agilatech® Lynxari IoT Platform. Please see agilatech.com to download a copy of the system.

Install

$> npm install lynxari-mpu9250-device

Design

This device driver is designed for both streaming and periodic monitored data collection from the MPU9250 sensor. This sensor supplies 3-axis data for acceleration, gyroscope, and magnetism, for a total of 9 values. Because a fair amount of overhead is required to poll the device for any one value, the hardware driver simply grabs all 9 values at once periodically. This period is configurable.

Usage

This device driver is designed to be consumed by the Agilatech® Lynxari IoT system. As such, it is not really applicable or useful in other environments.

To use it with Lynxari, insert its object definition as an element in the devices array in the devlist.json file.

{
  "name": "MPU9250",
  "module": "@agilatech/lynxari-mpu9250-device",
  "options": {
    "devicePoll": 1000,
    "streamPeriod": 60000,
    "bus":"/dev/i2c-1",
    "rate":300
  }
}

Device config object

The device config object is an element in the devlist.json device configuration file, which is located in the Lynxari root directory. It is used to tell the Lynxari system to load the device, as well as several operational parameters.

name is simply the name given to the device. This name can be used in queries and for other identifcation purposes.

module is the name of the npm module. The module is expected to exist in this directory under the node_modules directory. If the module is not strictly an npm module, it must still be found under the node_modules directory.

options is an object within the device config object which defines all other operational parameters. In general, any parameters may be defined in this options object, and most modules will have many several. The three which are a part of every Lynxari device are 'devicePoll', 'streamPeriod', and 'deltaPercent'. The deviceName options also can define FIXME: list all other addtional driver options. Finally, all parameter values can have a range defined by specifying '_range'.

"streamPeriod":<period>
Period in milliseconds for broadcast of streaming values

"devicePoll":<period>
Period in milliseconds in which device will be polled to check for new data

"deltaPercent":<percent>
Percent of the data range which must be exceeded (delta) to qualify as "new" data

"bus":<linux bus device>
Linux filesystem device for hardware bus, i.e. /dev/i2c-1

"addr":<i2c address>
Address on the I2C bus for which this device is located.  Defaults to 0x68.

"rate":<refresh rate>
Time in milliseconds on which all 9 values will be polled and loaded as the current.

devicePoll and streamPeriod

devicePoll is given in milliseconds, and defines how often the device will be polled for new values. This paramter is primary useful in sensors which sit idle waiting to be polled, and not for devices which supply values on their own schedule (i.e. for pull ranther that push).

streamPeriod is also given in milliseconds, and defines how often the device will publish its values on the data stream. Streaming is disabled if this parameter is set to 0.

deltaPercent explained

deltaPercent is the percentage of the current numerical data range which a polled data value must exceed to be considred "new". As an example, consider a temperature range of 100, a deltaPercent of 2, and the current temerature of 34. In such a case, a device poll must produce a value of 36 or greater, or 32 or less than in order to be stored as a current value. 35 or 33 will be ignored. deltaPercent may be any value greater than 0 or less than 100, and may be fractional. If not defined, the default is 5 percent.

bus file for Linux-based I2C access

bus defines the device file on Linux-based systems from which to read and write data. Since this driver is tightly coupled with the lower level hardware driver, it will not work with Windows-based systems.

Defining the value ranges

Value ranges may also be defined in the config, and are closely related to deltaPercent. If not defined, the software will keep track of minimum and maximum values and derive the range from them. However, that takes time for the software to "learn" the ranges, so they can be defined in the config object:

"accelx_range":<numeric range>
"accely_range":<numeric range>
"accelz_range":<numeric range>
"gyrox_range":<numeric range>
"gyroy_range":<numeric range>
"gyroz_range":<numeric range>
"magx_range":<numeric range>
"magy_range":<numeric range>
"magz_range":<numeric range>

where the <numeric range> is a number representing the absolute range of the value.

module config

Every module released by Agilatech includes configuration in a file named 'config.json' and we encourage any other publishers to follow the same pattern. The parameters in this file are considered defaults, since they are overriden by definitions appearing in the options object of the Lynxari devlist.json file.

The construction of the config.json mirrors that of the options object, which is simply a JSON object with key/value pairs. Here is an example of an 'config.json' file which streams values every 10 seconds, polls the device every second, requires an 8% delta change to register a new monitored value:

{
    "streamPeriod":10000, 
    "devicePoll":1000, 
    "deltaPercent":8
}

Default values

If not specified in the config object, the program uses the following default values:

• streamPeriod : 10000 (10,000ms or 10 seconds)
• devicePoll : 1000 (1,000ms or 1 second)
• deltaPercent : 5 (polled values must exceed the range by ± 5%)
• bus : /dev/i2c-2
• addr : 0x68
• rate : 500 (poll and store all values every 1/2 second)

Properties

All drivers contain the following 4 core properties:

1. state : the current state of the device, containing either the value chron-on or chron-off to indicate whether the device is monitoring data isochronally (a predefinied uniform time period of device data query).
2. id : the unique id for this device. This device id is used to subscribe to this device streams.
3. name : the given name for this device.
4. type : the given type category for this device, (sensor, actuator, etc)

Monitored Properties

In the on state, the driver software for this device monitors three values.

1. accelx : accelerometer x-axis value

2. accely : accelerometer y-axis value

3. accelz : accelerometer z-axis value

4. gyrox : gyro x-axis value

5. gyroy : gyro y-axis value

6. gyroz : gyro z-axis value

7. magx : magnetometer x-axis value

8. magy : magnetometer y-axis value

9. magz : magnetometer z-axis value

Streaming Properties

In the on state, the driver software continuously streams FIXME:three values in isochronal fashion with a period defined by streamPeriod. Note that a streamPeriod of 0 disables streaming.

1. accelx_stream
2. accely_stream
3. accelz_stream
4. gyrox_stream
5. gyroy_stream
6. gyroz_stream
7. magx_stream
8. magy_stream
9. magz_stream

State

This device driver has a binary state: on or off. When off, no parameter values are streamed or available, and no commands are accepted other than the turn-on transition. When on, the device is operations and accepts all commands. The initial state is off.

Transitions

1. turn-on : Sets the device state to on. When on, the device is operational and accepts all commands. Values are streamed, and the device is polled periodically to keep monitored values up to date.

2. turn-off : Sets the device state to off, When off, no parameter values are streamed or available, and no commands are accepted other than the turn-on transition.

Compatibility

This driver is designed to run within the Lynxari IoT platform. While Lynxari will run on nearly any operating system, this driver employs UNIX-specific protocols and as such will run on the following operating systems:

• 32 or 64-bit Linux
• macOS and OS X
• SunOS
• AIX

Copyright

Copyright © 2018 Agilatech®. All Rights Reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.