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Update BME688 gas resistance calculation #909

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merged 2 commits into from
Feb 23, 2024
Merged

Update BME688 gas resistance calculation #909

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378684e
Fix xml comment on BME280
adrianstevens Feb 23, 2024
16ffa80
Update calculation and registers for gas resistance
adrianstevens Feb 23, 2024
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2 changes: 1 addition & 1 deletion Source/Meadow.Foundation.Peripherals/Sensors.Atmospheric.Bme280/Driver/Bme280.cs
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Expand Up @@ -148,7 +148,7 @@ public SpiClockConfiguration.Mode SpiBusMode
/// Initializes a new instance of the BME280 class
/// </summary>
/// <param name="i2cBus">I2C Bus to use for communicating with the sensor</param>
/// <param name="address">I2C address of the sensor (default = 0x77)</param>
/// <param name="address">I2C address of the sensor (default = 0x76)</param>
public Bme280(II2cBus i2cBus, byte address = (byte)Addresses.Default)
{
bme280Comms = new I2cCommunications(i2cBus, address);
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4 changes: 2 additions & 2 deletions Source/Meadow.Foundation.Peripherals/Sensors.Atmospheric.Bme68x/Driver/Bme68x.Registers.cs
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Expand Up @@ -47,8 +47,8 @@ internal enum Registers : byte
TEMPDATA = 0x22,
HUMIDITYDATA = 0x25,

GAS_RES = 0x2A,
GAS_RANGE = 0x2B,
GAS_RES = 0x2C,
GAS_RANGE = 0x2D,
RES_HEAT_0 = 0x5A,
GAS_WAIT_0 = 0x64,

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11 changes: 6 additions & 5 deletions Source/Meadow.Foundation.Peripherals/Sensors.Atmospheric.Bme68x/Driver/Bme68x.cs
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Expand Up @@ -138,7 +138,7 @@ public bool GasConversionIsEnabled
{
var gasConversion = busComms.ReadRegister((byte)Registers.CTRL_GAS_1);
byte mask = 0x10;
gasConversion = (byte)((gasConversion & (byte)~mask) | Convert.ToByte(value) << 4);
gasConversion = (byte)((gasConversion & (byte)~mask) | Convert.ToByte(value) << 5);

busComms.WriteRegister((byte)Registers.CTRL_GAS_1, gasConversion);
gasConversionIsEnabled = value;
Expand Down Expand Up @@ -587,10 +587,11 @@ private Resistance CalculateGasResistance(ushort adcGasRes, byte gasRange)
{
if (calibration == null) throw new NullReferenceException("Calibration must be defined");

var var1 = 1340.0 + 5.0 * calibration.RangeSwErr;
var var2 = var1 * (1.0 + k1Lookup[gasRange] / 100.0);
var var3 = 1.0 + k2Lookup[gasRange] / 100.0;
var gasResistance = 1.0 / (var3 * 0.000000125 * (1 << gasRange) * ((adcGasRes - 512.0) / var2 + 1.0));
var var1 = ((uint)262144) >> gasRange;
var var2 = (adcGasRes) - 512;
var2 *= 3;
var2 = 4096 + var2;
var gasResistance = 1_000_000.0 * var1 / var2;

return new Resistance(gasResistance, Resistance.UnitType.Ohms);
}
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