From 3b251901addff6b2df196d6f9bb012a5ec168c6c Mon Sep 17 00:00:00 2001
From: Uwe Fechner <u.fechner-1@tudelft.nl>
Date: Tue, 19 Nov 2024 21:28:10 +0100
Subject: [PATCH] add delay function

---
 examples/test_delay.jl | 41 +++++++++++++++++++++++++++++++++++++++++
 src/DiscreteFilters.jl | 11 ++++++++++-
 2 files changed, 51 insertions(+), 1 deletion(-)
 create mode 100644 examples/test_delay.jl

diff --git a/examples/test_delay.jl b/examples/test_delay.jl
new file mode 100644
index 0000000..d168ea0
--- /dev/null
+++ b/examples/test_delay.jl
@@ -0,0 +1,41 @@
+using DiscreteFilters, ControlPlots
+
+# Define the cut-off frequency in Hz
+cut_off_freq = 2.0
+
+# Define the sampling time in seconds
+dt = 0.05
+sim_time = 4.0
+N = Int(sim_time / dt)
+
+# Design the filter
+butter = create_filter(cut_off_freq; order=4, dt)
+cheby1 = create_filter(cut_off_freq; order=4, type=:Cheby1, dt)
+
+# Create an array of measurements
+measurements = zeros(N)
+for i in Int(N/2):N
+    measurements[i] = 1.0
+end
+
+results = zeros(N)
+
+# Apply the EMA filter
+last_measurement::Float64 = 0.0
+for i in 1:N
+    global last_measurement
+    results[i] = ema_filter(measurements[i], last_measurement, cut_off_freq, dt)
+    last_measurement = results[i]
+end
+
+# Apply the Butterworth filter
+buffer = zeros(N)
+results_delay = zeros(N)
+for i in 1:N
+    results_delay[i] = apply_delay(measurements[i], buffer, i; delay=5)
+end
+
+
+# Plot the results
+plot((1:N)*dt, [measurements, results, results_delay]; xlabel="Time (s)", ylabel="Amplitude", 
+     fig="Delay of 5 samples")
\ No newline at end of file
diff --git a/src/DiscreteFilters.jl b/src/DiscreteFilters.jl
index 3bb4a6c..8be82aa 100644
--- a/src/DiscreteFilters.jl
+++ b/src/DiscreteFilters.jl
@@ -2,7 +2,7 @@ module DiscreteFilters
 
 using DSP
 
-export ema_filter, create_filter, apply_filter
+export ema_filter, create_filter, apply_filter, apply_delay
 
 """
     ema_filter(measurement, last_measurement, cut_off_freq, dt)
@@ -66,4 +66,13 @@ function apply_filter(butter, measurement, buffer, index)
     return res[index]
 end
 
+function apply_delay(measurement, buffer, index; delay=1)
+    buffer[index] = measurement
+    if index-delay < 1
+        return measurement
+    else
+        return buffer[index-delay]
+    end
+end
+
 end