From 22c92da97ce5e11ae8774cbc06e85be2583f06f1 Mon Sep 17 00:00:00 2001
From: "pls.153" <pls.153@protonmail.com>
Date: Thu, 23 Mar 2023 18:14:37 +0100
Subject: [PATCH] add snippet 'sensor-reading'

---
 snippets/sensor-reading/qml/main.qml | 23 +++++++++++++++++++++++
 snippets/sensor-reading/readme.md    |  5 +++++
 snippets/sensor-reading/run.lisp     | 28 ++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+)
 create mode 100644 snippets/sensor-reading/qml/main.qml
 create mode 100644 snippets/sensor-reading/readme.md
 create mode 100644 snippets/sensor-reading/run.lisp

diff --git a/snippets/sensor-reading/qml/main.qml b/snippets/sensor-reading/qml/main.qml
new file mode 100644
index 0000000..3858beb
--- /dev/null
+++ b/snippets/sensor-reading/qml/main.qml
@@ -0,0 +1,23 @@
+import QtQuick 2.15
+import QtSensors 5.15
+
+Rectangle {
+  width: 300
+  height: 500
+
+  Accelerometer {
+    id: accel
+    active: true
+    accelerationMode: Accelerometer.User // exclude gravity
+  }
+
+  Timer {
+    id: timer
+    interval: 50
+    repeat: true
+    running: true
+
+    onTriggered: Lisp.call("qml-user:accel-changed",
+                           accel.reading.x, accel.reading.y, accel.reading.z)
+  }
+}
diff --git a/snippets/sensor-reading/readme.md b/snippets/sensor-reading/readme.md
new file mode 100644
index 0000000..477eb88
--- /dev/null
+++ b/snippets/sensor-reading/readme.md
@@ -0,0 +1,5 @@
+Description
+-----------
+
+Shows how to read sensor data with a timer, plus a trivial low-pass filter.
+
diff --git a/snippets/sensor-reading/run.lisp b/snippets/sensor-reading/run.lisp
new file mode 100644
index 0000000..680a739
--- /dev/null
+++ b/snippets/sensor-reading/run.lisp
@@ -0,0 +1,28 @@
+(in-package :qml-user)
+
+;;; low-pass filter
+
+(defun make-low-pass-filter (&optional (alpha 0.02))
+  (let ((a alpha)
+        filtered)
+    (lambda (value)
+      (setf filtered (if filtered
+                         (+ (* value a)
+                            (* filtered (- 1.0 a)))
+                         value)))))
+
+(defvar *accel-x* (make-low-pass-filter))
+(defvar *accel-y* (make-low-pass-filter))
+(defvar *accel-z* (make-low-pass-filter))
+
+;;; sensor data
+
+(defun hr (x)
+  "Human readable."
+  (floor (+ 0.5 (* 1000 x))))
+
+(defun accel-changed (x y z)
+  (qlog :x (hr (funcall *accel-x* x)))
+  (qlog :y (hr (funcall *accel-y* y)))
+  (qlog :z (hr (funcall *accel-z* z))))
+