1 files changed, 27 insertions, 0 deletions
diff --git a/src/components/heartrate/Biquad.cpp b/src/components/heartrate/Biquad.cpp
new file mode 100644
index 00000000..6a4b8181
--- /dev/null
+++ b/src/components/heartrate/Biquad.cpp
@@ -0,0 +1,27 @@
+/*
+  SPDX-License-Identifier: LGPL-3.0-or-later
+  Original work Copyright (C) 2020 Daniel Thompson
+  C++ port Copyright (C) 2021 Jean-François Milants
+*/
+
+#include "Biquad.h"
+
+using namespace Pinetime::Controllers;
+
+/** Original implementation from wasp-os : https://github.com/daniel-thompson/wasp-os/blob/master/wasp/ppg.py */
+Biquad::Biquad(float b0, float b1, float b2, float a1, float a2) : b0{b0}, b1{b1}, b2{b2}, a1{a1}, a2{a2} {
+
+}
+
+float Biquad::Step(float x) {
+  auto v1 = this->v1;
+  auto v2 = this->v2;
+
+  auto v = x - (a1 * v1) - (a2 * v2);
+  auto y = (b0 * v) + (b1 * v1) + (b2 * v2);
+
+  this->v2 = v1;
+  this->v1 = v;
+
+  return y;
+}