From 8f5fcdc8ec29a74f8bd90f9edd93484570813b37 Mon Sep 17 00:00:00 2001
From: Ilya Rodichev <ilya@rodichev.com>
Date: Sat, 25 Jan 2025 19:22:32 +0300
Subject: [PATCH] enable IIR filtering for BME280

---
 airrohr-firmware/airrohr-firmware.ino |  3 ++-
 airrohr-firmware/bmx280_i2c.cpp       |  2 ++
 airrohr-firmware/bmx280_i2c.h         | 30 +++++++++++++++++++++------
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/airrohr-firmware/airrohr-firmware.ino b/airrohr-firmware/airrohr-firmware.ino
index 7b6b4cb47..9ea796237 100644
--- a/airrohr-firmware/airrohr-firmware.ino
+++ b/airrohr-firmware/airrohr-firmware.ino
@@ -5408,7 +5408,8 @@ static bool initBMX280(char addr)
 			BMX280::MODE_FORCED,
 			BMX280::SAMPLING_X1,
 			BMX280::SAMPLING_X1,
-			BMX280::SAMPLING_X1);
+			BMX280::SAMPLING_X1,
+			BMX280::IIR_16);
 		return true;
 	}
 	else
diff --git a/airrohr-firmware/bmx280_i2c.cpp b/airrohr-firmware/bmx280_i2c.cpp
index 562953569..b89d9a657 100644
--- a/airrohr-firmware/bmx280_i2c.cpp
+++ b/airrohr-firmware/bmx280_i2c.cpp
@@ -129,6 +129,7 @@ void BMX280::setSampling(sensor_mode mode,
                                   sensor_sampling tempSampling,
                                   sensor_sampling pressSampling,
                                   sensor_sampling humSampling,
+                                  iir_filter iirFilter,
                                   standby_duration duration) {
 
   _measReg.mode = mode;
@@ -140,6 +141,7 @@ void BMX280::setSampling(sensor_mode mode,
 
   config _configReg;
   _configReg.t_sb = duration;
+  _configReg.filter = iirFilter;
 
   // making sure sensor is in sleep mode before setting configuration
   // as it otherwise may be ignored
diff --git a/airrohr-firmware/bmx280_i2c.h b/airrohr-firmware/bmx280_i2c.h
index e7138f8fc..bc2fd6c65 100644
--- a/airrohr-firmware/bmx280_i2c.h
+++ b/airrohr-firmware/bmx280_i2c.h
@@ -50,6 +50,19 @@ class BMX280 {
     SAMPLING_X16 = 0b101
   };
 
+  /**************************************************************************/
+  /*!
+      @brief  IIR filter
+  */
+  /**************************************************************************/
+  enum iir_filter {
+    IIR_NONE = 0b000,
+    IIR_2 = 0b001,
+    IIR_4 = 0b010,
+    IIR_8 = 0b011,
+    IIR_16 = 0b100
+  };
+
   /**************************************************************************/
   /*!
       @brief  power modes
@@ -82,6 +95,7 @@ class BMX280 {
                    sensor_sampling tempSampling = SAMPLING_X16,
                    sensor_sampling pressSampling = SAMPLING_X16,
                    sensor_sampling humSampling = SAMPLING_X16,
+                   iir_filter iirFilter = IIR_NONE,
                    standby_duration duration = STANDBY_MS_0_5);
 
   void takeForcedMeasurement();
@@ -146,14 +160,18 @@ class BMX280 {
     // 111 = 20 ms
     uint8_t t_sb : 3; ///< inactive duration (standby time) in normal mode
 
-    // unused - don't set
-    uint8_t none : 1;     ///< unused - don't set
+    // Controls the time constant of the IIR filter
+    // 000 = off
+    // 001 = 2
+    // 010 = 4
+    // 011 = 8
+    // 100, others = 16
+    uint8_t filter : 3; ///< Controls the time constant of the IIR filter
+    uint8_t none : 1; ///< unused - don't set
     uint8_t spi3w_en : 1; ///< unused - don't set
-
-    uint8_t _unused : 3;
-
+    
     /// @return combined config register
-    uint8_t get() { return (t_sb << 5); }
+    uint8_t get() { return (t_sb << 5) | (filter << 2); }
   };
 
   /**************************************************************************/