From 3bfc9d6abfe681e610f4e1eb3cb01f008f3bfbbf Mon Sep 17 00:00:00 2001
From: Tellicious <tellicious@icloud.com>
Date: Sat, 1 Jun 2024 00:01:33 +0200
Subject: [PATCH] Added band-pass and band-stop filter coefficients calculation
 to IIRFilters.c

---
 .github/releaseBody.md |  7 +++++--
 Changelog.md           |  9 ++++++++-
 inc/IIRFilters.h       | 22 +++++++++++++++++++++-
 src/IIRFilters.c       | 25 ++++++++++++++++++++++++-
 4 files changed, 58 insertions(+), 5 deletions(-)

diff --git a/.github/releaseBody.md b/.github/releaseBody.md
index 5815b4a..63a5572 100644
--- a/.github/releaseBody.md
+++ b/.github/releaseBody.md
@@ -1,6 +1,9 @@
-## Added assertions to verify correctness of parameters
+## Added band-pass and band-stop filter coefficients calculation to IIRFilters.c
 
 **Improvements:**
-- Added assertions to `matrix.c` and `numMethods.c`
+- Added band-pass and band-stop filter coefficients calculation to `IIRFilters.c` to simplify initialization
+
+**Bugfix:**
+- Fixed minor bug in `IIRFilters.c`
 
 See [Changelog](Changelog.md)
\ No newline at end of file
diff --git a/Changelog.md b/Changelog.md
index 5c846c8..fae7c95 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## v1.12.0
+
+**Improvements:**
+- Added band-pass and band-stop filter coefficients calculation to `IIRFilters.c` to simplify initialization
+
+**Bugfix:**
+- Fixed minor bug in `IIRFilters.c`
+
 ## v1.11.1
 
 **Improvements:**
@@ -100,7 +108,6 @@
 - Fixed snippets
 - Renamed a few variables inside PID object
 
-
 ## v1.2.0
 
 **Improvements:**
diff --git a/inc/IIRFilters.h b/inc/IIRFilters.h
index 2ea3085..bfd59dd 100644
--- a/inc/IIRFilters.h
+++ b/inc/IIRFilters.h
@@ -98,11 +98,31 @@ void IIRFilterInitLP(IIRFilterGeneric_t* filter, float lpFreq, float dT_ms);
  * \brief           Initialize second-order Butterworth high-pass IIR filter
  *
  * \param[in]       filter: pointer to IIR filter structure
- * \param[in]       hpFreq: low-pass cutoff frequency in Hz
+ * \param[in]       hpFreq: high-pass cutoff frequency in Hz
  * \param[in]       dT_ms: sampling time in ms
  */
 void IIRFilterInitHP(IIRFilterGeneric_t* filter, float hpFreq, float dT_ms);
 
+/**
+ * \brief           Initialize second-order Butterworth band-pass IIR filter
+ *
+ * \param[in]       filter: pointer to IIR filter structure
+ * \param[in]       centerFreq: center frequency of pass-band in Hz
+ * \param[in]       bandwidth: bandwidth of pass-band in Hz. Response will be symmetrical around centerFreq on a logarithmic scale
+ * \param[in]       dT_ms: sampling time in ms
+ */
+void IIRFilterInitBP(IIRFilterGeneric_t* filter, float centerFreq, float bandwidth, float dT_ms);
+
+/**
+ * \brief           Initialize second-order Butterworth band-stop IIR filter
+ *
+ * \param[in]       filter: pointer to IIR filter structure
+ * \param[in]       centerFreq: center frequency of stop-band in Hz
+ * \param[in]       bandwidth: bandwidth of stop-band in Hz. Response will be symmetrical around centerFreq on a logarithmic scale
+ * \param[in]       dT_ms: sampling time in ms
+ */
+void IIRFilterInitBS(IIRFilterGeneric_t* filter, float centerFreq, float bandwidth, float dT_ms);
+
 /**
  * \brief           Apply generic IIR filter to provided sample
  *
diff --git a/src/IIRFilters.c b/src/IIRFilters.c
index 67750c7..8856275 100644
--- a/src/IIRFilters.c
+++ b/src/IIRFilters.c
@@ -64,7 +64,7 @@ void IIRFilterInitLP(IIRFilterGeneric_t* filter, float lpFreq, float dT_ms) {
 }
 
 void IIRFilterInitHP(IIRFilterGeneric_t* filter, float hpFreq, float dT_ms) {
-    const float lambda = 1.f / TAN(3.141592653f * (hpFreq * dT_ms * 1e-3f));
+    const float lambda = 1.f / TAN(constPI * (hpFreq * dT_ms * 1e-3f));
     const float q = SQRT(2.f);
     float n0 = 1.f / (1.f + q * lambda + lambda * lambda);
     float n1 = -2.f * n0 * lambda * lambda;
@@ -74,6 +74,29 @@ void IIRFilterInitHP(IIRFilterGeneric_t* filter, float hpFreq, float dT_ms) {
     IIRFilterInit(filter, n0, n1, n0, 0, d1, d2, 0);
 }
 
+void IIRFilterInitBP(IIRFilterGeneric_t* filter, float centerFreq, float bandwidth, float dT_ms) {
+    const float Q = centerFreq / bandwidth; // Q factor
+    const float C = TAN(constPI * (centerFreq * dT_ms * 1e-3f));
+    const float D = 1.f / (1.f + C / Q + C * C);
+    float n0 = C / Q * D;
+    float n2 = -n0;
+    float d1 = 2.f * (C * C - 1.f) * D;
+    float d2 = (1.f - C / Q + C * C) * D;
+    IIRFilterInit(filter, n0, 0, n2, 0, d1, d2, 0);
+}
+
+void IIRFilterInitBS(IIRFilterGeneric_t* filter, float centerFreq, float bandwidth, float dT_ms) {
+    const float Q = centerFreq / bandwidth; // Q factor
+    const float C = TAN(constPI * (centerFreq * dT_ms * 1e-3f));
+    const float D = 1.f / (1.f + C / Q + C * C);
+    float n0 = (1.f + C * C) * D;
+    float n1 = 2.f * (C * C - 1.f) * D;
+    float n2 = n0;
+    float d1 = 2.f * (C * C - 1.f) * D;
+    float d2 = (1.f - C / Q + C * C) * D;
+    IIRFilterInit(filter, n0, n1, n2, 0, d1, d2, 0);
+}
+
 float IIRFilterProcess(IIRFilterGeneric_t* filter, float input) {
     /* Apply the IIR filter equation */
     float output;