async-bmp280

   !CircleCI  

JavaScript interface to control the temperature and pressure sensors BMP280, like the one used in the Enviro pHat. The BMP280Interface extends the DeviceInterface of async-i2c-bus.

Installation

To use this library you will also have to install async-i2c-bus.

Yarn:

``bash
yarn add async-i2c-bus async-i2c-bus
`

or npm:

`bash
npm i -P async-i2c-bus async-i2c-bus
`

And you're ready to go.

$3

The package requires node v8.10.x or higher.
If you need a compatibility with lower versions of node, you can build it. To do so clone the repo in your workspace, and modify the target options in the tsconfig.json, e.g:

`js
{
"compilerOptions": {
"target": "es5", // <-- Line changed
"outDir": "dist/main",
"rootDir": "src",
// ..
}
}
`

And build the module with yarn build or npm run build.

Usage

The BMP280 factory takes as argument an instance of the BusInterface and returns an instance of the BMP280Interface.

`javascript
function BMP280({ bus }: { bus: BusInterface }): BMP280Interface;
`

The BMP280Interfaces inherits from DeviceInterface, hence all the low level methods such as writeByte, readByte,... are available to work with the device.

But it also offers some specific methods to work with the sensor.

$3

The init method performs a reset of the device, acquires temperature/pressure correction and configures the device with the values selected (if none present, it will use the default ones):

`javascript
init(params?: Partial): Promise;
`

The interfaces in the params are:

`javascript
interface BMP280ControlMeasurement {
temperatureOversampling: BMP280Oversampling;
pressureOversampling: BMP280Oversampling;
mode: BMP280Mode;
}
interface BMP280Config {
standbyTime: BMP280StandbyTime;
iirFilter: BMP280IirFilter;
}

// Types:
type BMP280Oversampling = 'x0' | 'x1' | 'x2' | 'x4' | 'x8' | 'x16';
type BMP280Mode = 'SLEEP' | 'FORCED' | 'NORMAL';
type BMP280StandbyTime = '500us' | '62ms' | '125ms' | '250ms' | '500ms' | '1s' | '2s' | '4s';
type BMP280IirFilter = 'x0' | 'x1' | 'x2' | 'x4' | 'x8' | 'x16';
`

This is the recommended way of initializing the sensor.

If you don't use it, be sure to call readTemperatureCorrection and readPressureCorrection to be able to read the right temperature/pressure values.

Example of init vs no init

`javascript
import { Bus } from 'async-i2c-bus';
import { BMP280, REGISTERS, OFFSETS, OVERSAMPLING, MODE, STANDBY_TIME, IIR_FILTER } from 'async-i2c-bus';

// ...

const bus = Bus();
await bus.open();

const bmp280 = BMP280({ bus });

// init version
await bmp280.init();

// no-init version;

await bmp280.reset();
await bmp280.readTemperatureCorrection();
await bmp280.readPressureCorrection();

await bmp280.writeByte(
REGISTERS.CTRL_MEAS,
(OVERSAMPLING.x1 << OFFSETS.OSRS_T) | (OVERSAMPLING.x1 << OFFSETS.OSRS_P) | MODE.NORMAL,
);
await bmp280.writeByte(REGISTERS.CONFIG, (STANDBY_TIME['500us'] << OFFSETS.T_SB) | (IIR_FILTER.x16 << OFFSETS.FILTER));
`

After this step, the device is ready to readTemperature and to readPressure.

For more details, check the full auto-generated documentation and get familiar with BMP280 datasheet.

$3

The module exports
There's two handy methods to read/write the registers config and ctrl_meas.

#### write

`javascript
writeControlMeasurement(controlMeasurement: Partial): Promise
writeConfig(controlMeasurement: Partial): Promise
`

Both functions will apply the values passed in the argument and apply them on the current value. That means that it is possible to change only one value or more in the register and leave the rest untouched.

`javascript
await bmp280.writeConfig({ iirFilter: 'x16' });

// it is equivalent as:

const currentValue = await bmp280.readByte(REGISTERS.config);
const nextValue = (currentValue ^ (MASKS.FILTER << OFFSETS.FILTER)) | (IIR_FILTER.x16 << OFFSETS.FILTER);
await bmp280.writeByte(REGISTERS.CONFIG, nextValue);
`

#### read

Read is the inverse function of the previous two functions:

`javascript
readControlMeasurement(): Promise
readConfig(): Promise
`

Example:

`javascript
await bmp280.writeConfig({ iirFilter: 'x16', standbyTime: '4s' });
await bmp280.readConfig(); // Returns { iirFilter: 'x16', standbyTime: '4s' }
`

$3

`javascript
readTemperature(): Promise
readPressure(): Promise
`

Read temperature returns the celsius degrees.
Read pressure returns the pressure in Pascals.

$3

In case that you want or need to work with lower level method, the module exposes several constants to work with:

- REGISTERS
- MASKS
- OFFSETS
- OVERSAMPLING
- MODE
- STANDBY_TIME
- IIR_FILTER

Example:

`javascript
// ...
await bmp280.writeByte(
REGISTERS.CTRL_MEAS,
(OVERSAMPLING.x1 << OFFSETS.OSRS_T) | (OVERSAMPLING.x1 << OFFSETS.OSRS_P) | MODE.NORMAL,
);

const ctrlMeas = await bmp280.readByte(REGISTERS.CTRL_MEAS);
const temperatureOversampling = (ctrlMeas & MASKS.OSRS_T) >>> OFFSETS.OSRS_T;
`

$3

`javascript
import { Bus } from 'async-i2c-bus';
import { BMP280 } from 'async-i2c-bus';

const main = async () => {
const busNumber = 1;
const bus = Bus({ busNumber });

await bus.open();

const bmp280 = BMP280({ bus });

await bmp280.init();

let temperature = 0;
let pressure = 0;

/* Read temperature/pressure every second /
while (1) {
[temperature, pressure] = await Promise.all([bmp280.readTemperature(), bmp280.readPressure()]);

console.log(Temperature: ${temperature}°C);
console.log(Pressure: ${pressure}Pa);

await new Promise(resolve => {
setTimeout(() => {
resolve();
}, 1000);
});
}
};
`

$3

`javascript
import { Bus } from 'async-i2c-bus';
import { BMP280, IIR_FILTER, MODE, OVERSAMPLING } from 'async-i2c-bus';

const main = async () => {
const busNumber = 1;
const bus = Bus({ busNumber });

await bus.open();

const bmp280 = BMP280({ bus });

// Use your values
await bmp280.init({
temperatureOversampling: OVERSAMPLING.x16,
pressureOversampling: OVERSAMPLING.x16,
mode: MODE.FORCED,
iirFilter: IIR_FILTER.x0,
});

/* Read temperature/pressure once /
const [temperature, pressure] = await Promise.all([bmp280.readTemperature(), bmp280.readPressure()]);

console.log(Temperature: ${temperature}°C);
console.log(Pressure: ${pressure}Pa);
};
``