From 8f78143ecccece03877185a789d0b5e3d0040cc3 Mon Sep 17 00:00:00 2001
From: fleur <spacecarrot@fleurshax.net>
Date: Wed, 23 Oct 2019 16:10:21 +0200
Subject: [PATCH] added filter doc and cleaned up a bit
---
preload/apps/ecg/__init__.py | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/preload/apps/ecg/__init__.py b/preload/apps/ecg/__init__.py
index 53e4795fc..59466effc 100644
--- a/preload/apps/ecg/__init__.py
+++ b/preload/apps/ecg/__init__.py
@@ -51,12 +51,13 @@ last_sample_count = 1
leds.dim_top(1)
COLORS = [((23 + (15 * i)) % 360, 1.0, 1.0) for i in range(11)]
-
# variables for high-pass filter
+# note: corresponds to 1st order hpf with -3dB at ~18.7Hz
+# general formula: f(-3dB)=-(sample_rate/tau)*ln(1-betadash)
moving_average = 0
alpha = 2
beta = 3
-
+betadash = beta/(alpha+beta)
def update_history(datasets):
global history, moving_average, alpha, beta, last_sample_count
@@ -64,7 +65,8 @@ def update_history(datasets):
for val in datasets:
if current_mode == MODE_FINGER:
history.append(val - moving_average)
- moving_average = (alpha * moving_average + beta * val) / (alpha + beta)
+ moving_average += betadash*(val-moving_average)
+ # identical to: moving_average = (alpha * moving_average + beta * val) / (alpha + beta)
else:
history.append(val)
--
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