These sensors measure temperature, humidity, pressure and air quality and can communicate over both SPI and I2C. For the moment, the BME280 is mostly implemented and the BME680 (which also includes air quality sensing) is not completed. The datasheets are:
The interface for the sensors are as follows:
type BME280 interface {
gopi.Driver
// Get Version
ChipIDVersion() (uint8, uint8)
// Get Mode
Mode() BME280Mode
// Return IIR filter co-officient
Filter() BME280Filter
// Return standby time
Standby() BME280Standby
// Return oversampling values osrs_t, osrs_p, osrs_h
Oversample() (BME280Oversample, BME280Oversample, BME280Oversample)
// Return current measuring and updating value
Status() (bool, bool, error)
// Return the measurement duty cycle (minimum duration between subsequent readings)
// in normal mode
DutyCycle() time.Duration
// Reset
SoftReset() error
// Set BME280 mode
SetMode(mode BME280Mode) error
// Set Oversampling
SetOversample(osrs_t, osrs_p, osrs_h BME280Oversample) error
// Set Filter
SetFilter(filter BME280Filter) error
// Set Standby mode
SetStandby(t_sb BME280Standby) error
// Return raw sample data for temperature, pressure and humidity
// Temperature in Celcius, Pressure in Pascals and humidity in
// %age
ReadSample() (float64, float64, float64, error)
// Return altitude in meters for given pressure in Pascals
AltitudeForPressure(atmospheric, sealevel float64) float64
}
type BME680 interface {
gopi.Driver
// Get ChipID
ChipID() uint8
// Reset
SoftReset() error
}
In order to create a sensor object, you can import the following modules anonymously into your application:
| Import | Module Name | Sensor | Interface |
|---|---|---|---|
| github.com/djthorpe/sensors/sys/bme280 | sensors/bme280/i2c | BME280 | I2C |
| github.com/djthorpe/sensors/sys/bme280 | sensors/bme280/spi | BME280 | I2C |
| github.com/djthorpe/sensors/sys/bme680 | sensors/bme680/i2c | BME680 | SPI |
| github.com/djthorpe/sensors/sys/bme680 | sensors/bme680/spi | BME680 | SPI |
For the I2C driver, you will also need to import the module github.com/djthorpe/gopi-hw/sys/i2c
anonymously, and for the SPI driver, import the module github.com/djthorpe/gopi-hw/sys/spi. For
example,
package main
import (
"os"
"fmt"
// Frameworks
"github.com/djthorpe/gopi"
"github.com/djthorpe/sensors"
// Modules
_ "github.com/djthorpe/sensors/sys/bme280"
_ "github.com/djthorpe/gopi-hw/sys/i2c"
)
const (
BME280 = "sensors/bme280/i2c"
)
func Main(app *gopi.AppInstance, done chan<- struct{}) error {
bme280 := app.ModuleInstance(BME280).(sensors.BME280)
fmt.Println("BME280=",bme280)
return nil
}
func main() {
config := gopi.NewAppConfig(BME280)
os.Exit(gopi.CommandLineTool(config, Main))
}
More information about wiring up the sensors and using the examples is given in the following sections.
The Bosch BME280 measures temperature, humidity and pressure. You can interface this device either through I2C or SPI. The datasheet is provided in the "doc" folder.
In order to connect it to the Raspberry Pi, here are the two configurations of the pins on the BME280 device. The AdaFruit product is listed here as an example but there are other ways to connect (more information is avilable at https://www.adafruit.com/product/2652). The pin numbers here are provided for connecting the AdaFruit product with a Raspberry PI and are for the physical board pins:
| BME280 Pin | I2C | SPI(0) | Description |
|---|---|---|---|
| Vin | 2 | 2 | 3-5VDC power in |
| 3Vo | 3.3V power out | ||
| GND | 6 | 6 | Ground |
| SCK | 5 | 23 | SPI/I2C Clock Pin |
| SDO/MISO | 21 | Serial Data Out | |
| SDI/SDA/MOSI | 3 | 19 | Serial Data In / I2C Data Pin |
| CS | 24 | Chip Select |
Using the I2C connection bus, the slave address defaults to 0x77.
In order to install and/or run the command-line tool, you need to deploy the correct flavour using tags. Here is how you can can install and/or run when you want to use the I2C flavour:
bash% cd $GOPATH/src/github.com/djthorpe/sensors
bash% go (run|install) -tags i2c cmd/bme280.go
When you want to install or run a version which communicates over the SPI bus:
bash% cd $GOPATH/src/github.com/djthorpe/sensors
bash% go (run|install) -tags spi cmd/bme280.go
The command line tool demonstrates everything you need to know about using the sensor interface. You can run it with one of the following commands:
bme280 resetResets the sensor and displays the sensor statusbme280 statusDisplays the current sensor statusbme280 measureMeasures Temperature, Pressure and/or Humidity
There are also various flags you can use in order to set filter, mode, oversampling or standby time. Here are the main flags you can use on the command line:
-filter uint
Set filter co-efficient (0,2,4,8,16)
-mode string
Set sensor mode (normal,forced,sleep)
-oversample uint
Set oversampling of measurements (0,1,2,4,8,16)
-standby float
Standby time between measurements in normal mode, ms (0.5,10,20,62.5,125,250,500,1000)
There are a set of additional flags you can also use, some of which are available for I2C and others for SPI:
-i2c.bus uint
I2C Bus (default 1)
-i2c.slave uint
I2C Slave address (default 0x77)
-spi.speed uint
SPI Communication Speed
-debug
Set debugging mode
-verbose
Verbose logging
-log.append
When writing log to file, append output to end of file
-log.file string
File for logging (default: log to stderr)
The modes of operation are essentailly "forced" or "normal". Forced mode can be used for one-off measurement, or otherwise you can read measurements with a particular duty cycle, which is a function of standby time and oversampling values. Here's an example of status output demonstrating this:
bash% bme280 status
+------------------------+----------------------+
| REGISTER | VALUE |
+------------------------+----------------------+
| chip_id | 0x60 |
| chip_version | 0x00 |
| mode | BME280_MODE_NORMAL |
| filter | BME280_FILTER_OFF |
| standby | BME280_STANDBY_500MS |
| duty cycle | 558ms |
| oversample temperature | BME280_OVERSAMPLE_8 |
| oversample pressure | BME280_OVERSAMPLE_8 |
| oversample humidity | BME280_OVERSAMPLE_8 |
| measuring | false |
| updating | false |
+------------------------+----------------------+
In this example, the standby time is 500ms, measurement time is 58ms and you shouldn't poll for new measurements more than once every 558ms (the duty cycle).
In forced mode only one measurement is taken before the sensor returns to sleep mode:
bash% bme280 -mode forced measure
+-------------+------------+
| MEASUREMENT | VALUE |
+-------------+------------+
| temperature | 20.03 °C |
| pressure | 998.61 hPa |
| altitude | 122.64 m |
| humidity | 53.52 %RH |
+-------------+------------+
The Bosch BME680 measures air quality in addition to temperature, humidity and pressure. You can interface this device either through I2C or SPI. The datasheet is provided in the "doc" folder.
The code to implement this sensor is still to be written.