From 1fd1f9e2ec8064232dcc89e8c00a1ccf6ab4e40a Mon Sep 17 00:00:00 2001
From: Ahmet Inan <inan@aicodix.de>
Date: Tue, 12 Feb 2019 09:40:26 +0100
Subject: [PATCH] added Schmitt trigger and edge triggers

---
 README.md  |  8 +++++++
 trigger.hh | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 trigger.hh

diff --git a/README.md b/README.md
index cff171b..c046fe3 100644
--- a/README.md
+++ b/README.md
@@ -56,6 +56,14 @@ The following [infinite impulse response](https://en.wikipedia.org/wiki/Infinite
 
 [atan](https://en.wikipedia.org/wiki/Inverse_trigonometric_functions) and [atan2](https://en.wikipedia.org/wiki/Atan2).
 
+### [trigger.hh](trigger.hh)
+
+Implemented are the following [trigger functions](https://en.wikipedia.org/wiki/Flip-flop_(electronics)):
+
+* [Schmitt trigger](https://en.wikipedia.org/wiki/Schmitt_trigger)
+* [Rising edge trigger](https://en.wikipedia.org/wiki/Signal_edge)
+* [Falling edge trigger](https://en.wikipedia.org/wiki/Signal_edge)
+
 ### [const.hh](const.hh)
 
 Some constants we need
diff --git a/trigger.hh b/trigger.hh
new file mode 100644
index 0000000..4ea6f2c
--- /dev/null
+++ b/trigger.hh
@@ -0,0 +1,64 @@
+/*
+Some trigger functions
+
+Copyright 2019 Ahmet Inan <inan@aicodix.de>
+*/
+
+#pragma once
+
+namespace DSP {
+
+template <typename TYPE>
+class SchmittTrigger
+{
+	TYPE treshold;
+	bool previous;
+public:
+	constexpr SchmittTrigger(TYPE treshold, bool previous = false) : treshold(treshold), previous(previous)
+	{
+	}
+	bool operator() (TYPE input)
+	{
+		if (previous) {
+			if (input < -treshold)
+				previous = false;
+		} else {
+			if (input > treshold)
+				previous = true;
+		}
+		return previous;
+	}
+};
+
+class FallingEdgeTrigger
+{
+	bool previous;
+public:
+	constexpr FallingEdgeTrigger(bool previous = false) : previous(previous)
+	{
+	}
+	bool operator() (bool input)
+	{
+		bool tmp = previous;
+		previous = input;
+		return tmp && !input;
+	}
+};
+
+class RisingEdgeTrigger
+{
+	bool previous;
+public:
+	constexpr RisingEdgeTrigger(bool previous = false) : previous(previous)
+	{
+	}
+	bool operator() (bool input)
+	{
+		bool tmp = previous;
+		previous = input;
+		return !tmp && input;
+	}
+};
+
+}
+