Remarks

Bh1750
Status
Source code	GitHub
Datasheet(s)	GitHub
NuGet package

The BH1750 is a light intensity sensor that communicates over I2C.

Code Example

Bh1750 sensor;

public override Task Initialize()
{
    Resolver.Log.Info("Initialize...");

    var i2c = Device.CreateI2cBus();
    sensor = new Bh1750(
        i2c,
        measuringMode: Mode.ContinuouslyHighResolutionMode, // the various modes take differing amounts of time.
        lightTransmittance: 1 // lower this to increase sensitivity, for instance, if it's behind a semi opaque window
        ); 

    // Example that uses an IObservable subscription to only be notified when the filter is satisfied
    var consumer = Bh1750.CreateObserver(
        handler: result => Resolver.Log.Info($"Observer: filter satisifed: {result.New.Lux:N2}Lux, old: {result.Old?.Lux:N2}Lux"),

        // only notify if the visible light changes by 100 lux (put your hand over the sensor to trigger)
        filter: result => {
            if (result.Old is { } old) { //c# 8 pattern match syntax. checks for !null and assigns var.
                // returns true if > 100lux change
                return ((result.New - old).Abs().Lux > 100);
            }
            return false;
        });
    sensor.Subscribe(consumer);

    // classical .NET events can also be used:
    sensor.Updated += (sender, result) => Resolver.Log.Info($"Light: {result.New.Lux:N2}Lux");

    return Task.CompletedTask;
}

public override async Task Run()
{
    var result = await sensor.Read();
    Resolver.Log.Info("Initial Readings:");
    Resolver.Log.Info($" Light: {result.Lux:N2}Lux");

    sensor.StartUpdating(TimeSpan.FromSeconds(1));
}

Sample project(s) available on GitHub

Wiring Example

To wire a Bh1750 to your Meadow board, connect the following:

Bh1750	Meadow Pin
GND	GND
SCL	D08 (SCL)
SDA	D07 (SDA)
VCC	3V3

It should look like the following diagram:

Characteristic	Locus
Inheritance	System.Object ObservableBase<Illuminance> SamplingSensorBase<Illuminance> PollingSensorBase<Illuminance> ByteCommsSensorBase<Illuminance> > Bh1750
Implements	ISamplingSensor<Illuminance> ISamplingSensor<Illuminance> IDisposable ILightSensor
Inherited Members	ByteCommsSensorBase<Illuminance>.Peripheral ByteCommsSensorBase<Illuminance>.ReadBuffer ByteCommsSensorBase<Illuminance>.WriteBuffer ByteCommsSensorBase<Illuminance>.Init(Int32, Int32) ByteCommsSensorBase<Illuminance>.Dispose(Boolean) ByteCommsSensorBase<Illuminance>.Dispose() PollingSensorBase<Illuminance>.StartUpdating(Nullable<TimeSpan>) PollingSensorBase<Illuminance>.StopUpdating() SamplingSensorBase<Illuminance>.samplingLock SamplingSensorBase<Illuminance>.Updated SamplingSensorBase<Illuminance>.SamplingTokenSource SamplingSensorBase<Illuminance>.Conditions SamplingSensorBase<Illuminance>.IsSampling SamplingSensorBase<Illuminance>.UpdateInterval SamplingSensorBase<Illuminance>.RaiseEventsAndNotify(IChangeResult<>) SamplingSensorBase<Illuminance>.Read() ObservableBase<Illuminance>.observers ObservableBase<Illuminance>.NotifyObservers(IChangeResult<>) Meadow.Foundation.ObservableBase<Illuminance>.Subscribe(IObserver<>) Meadow.Foundation.ObservableBase<Illuminance>.CreateObserver(Action<>, System.Nullable<Predicate<IChangeResult<UNIT>>>)
Namespace	Meadow.Foundation.Sensors.Light
Assembly	Bh1750.dll

Syntax

public class Bh1750 : ByteCommsSensorBase<Illuminance>, ISamplingSensor<Illuminance>, ISamplingSensor<Illuminance>, IDisposable, ILightSensor

Constructors

Bh1750(II2cBus, Byte, Bh1750.MeasuringModes, Double)

Create a new BH1750 light sensor object using a static reference voltage.

Declaration

public Bh1750(II2cBus i2cBus, byte address = null, Bh1750.MeasuringModes measuringMode = default(Bh1750.MeasuringModes), double lightTransmittance = null)

Parameters

Type	Name	Description
II2cBus	i2cBus
System.Byte	address
Bh1750.MeasuringModes	measuringMode
System.Double	lightTransmittance

Properties

Illuminance

The current illuminance read by the sensor

Declaration

public Illuminance? Illuminance { get; }

Property Value

Type	Description
System.Nullable<Illuminance>

LightTransmittance

BH1750 Light Transmittance (27.20-222.50%)

Declaration

public double LightTransmittance { get; set; }

Property Value

Type	Description
System.Double

MeasuringMode

BH1750 Measuring Mode

Declaration

public Bh1750.MeasuringModes MeasuringMode { get; set; }

Property Value

Type	Description
Bh1750.MeasuringModes

Methods

RaiseEventsAndNotify(IChangeResult<Illuminance>)

Raise events for subcribers and notify of value changes

Declaration

protected override void RaiseEventsAndNotify(IChangeResult<Illuminance> changeResult)

Parameters

Type	Name	Description
IChangeResult<Illuminance>	changeResult	The updated sensor data

ReadSensor()

Read the current luminocity

Declaration

protected override Task<Illuminance> ReadSensor()

Returns

Type	Description
Task<Illuminance>	The current Illuminance value

Overrides

Meadow.Foundation.SamplingSensorBase<Illuminance>.ReadSensor()

Events

LuminosityUpdated

Raised when a new Illuminance value is read by the sensor

Declaration

public event EventHandler<IChangeResult<Illuminance>> LuminosityUpdated

Event Type

Type	Description
EventHandler<IChangeResult<Illuminance>>