Fully working plot, server, and sensor with timestamps

main.go

@@ -12,20 +12,28 @@ import (
 )
 
 var dataFile *os.File
-var startTime time.Time
+var berlinTZ *time.Location
 
 type VoltageData struct {
 	Voltage float64 `json:"voltage"`
 }
 
+func init() {
+	var err error
+	berlinTZ, err = time.LoadLocation("Europe/Berlin")
+	if err != nil {
+		log.Fatalf("Failed to load Berlin timezone: %v", err)
+	}
+}
+
 func initDataFile() {
 	// Ensure the data/ directory exists
 	if err := os.MkdirAll("data", os.ModePerm); err != nil {
 		log.Fatalf("Failed to create data directory: %v", err)
 	}
 
-	// Generate a filename with timestamp
-	filename := filepath.Join("data", fmt.Sprintf("voltages_%s.csv", time.Now().Format("20060102_150405")))
+	// Generate a filename with timestamp in Berlin local time
+	filename := filepath.Join("data", fmt.Sprintf("voltages_%s.csv", time.Now().In(berlinTZ).Format("20060102_150405")))
 	file, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
 	if err != nil {
 		log.Fatalf("Failed to open data file: %v", err)
@@ -35,9 +43,7 @@ func initDataFile() {
 	log.Printf("Logging voltage data to %s\n", filename)
 
 	// Write CSV header
-	_, _ = dataFile.WriteString("time_s,voltage\n")
-
-	startTime = time.Now()
+	_, _ = dataFile.WriteString("timestamp,voltage\n")
 }
 
 func handler(w http.ResponseWriter, r *http.Request) {
@@ -60,15 +66,15 @@ func handler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Compute relative time
-	relTime := time.Since(startTime).Seconds()
+	// Get current timestamp in Berlin
+	timestamp := time.Now().In(berlinTZ).Format("2006-01-02 15:04:05.000")
 
 	// Print voltage to console
-	fmt.Printf("Received voltage: %f at time %.3f s\n", v.Voltage, relTime)
+	fmt.Printf("Received voltage: %f at %s\n", v.Voltage, timestamp)
 
 	// Append CSV line to file
 	if dataFile != nil {
-		if _, err := dataFile.WriteString(fmt.Sprintf("%.3f,%.6f\n", relTime, v.Voltage)); err != nil {
+		if _, err := dataFile.WriteString(fmt.Sprintf("%s,%.6f\n", timestamp, v.Voltage)); err != nil {
 			log.Printf("Failed to write to file: %v", err)
 		}
 	}

plot.py

@@ -1,7 +1,10 @@
 import os
 import matplotlib.pyplot as plt
+import matplotlib.dates as mdates
 import numpy as np
 
+from datetime import datetime
+
 DATA_DIR = "data"
 
 # Find the latest data file
@@ -13,18 +16,30 @@ latest_file = max(files, key=lambda f: os.path.getmtime(os.path.join(DATA_DIR, f
 filepath = os.path.join(DATA_DIR, latest_file)
 print(f"Plotting data from {filepath}")
 
-# Load CSV data (skip header)
-data = np.loadtxt(filepath, delimiter=",", skiprows=1)
-times = data[:, 0]
-voltages = data[:, 1]
+# Load CSV data
+timestamps = []
+voltages = []
+
+with open(filepath, "r") as f:
+    next(f)  # skip header
+    for line in f:
+        ts_str, v_str = line.strip().split(",")
+        ts = datetime.strptime(ts_str, "%Y-%m-%d %H:%M:%S.%f")
+        timestamps.append(ts)
+        voltages.append(float(v_str))
 
 # Plot
-plt.figure(figsize=(10, 5))
-plt.plot(times, voltages, marker='o', linestyle='-')
-plt.xlabel("Time (s)")
+plt.figure(figsize=(12, 5))
+plt.plot(timestamps, voltages, marker='o', linestyle='-')
+
+plt.xlabel("Time (CET)")
 plt.ylabel("Voltage (V)")
 plt.title(f"Voltage Measurements ({latest_file})")
 plt.grid(True)
+
+# Format x-axis for readable time
+plt.gcf().autofmt_xdate()
+plt.gca().xaxis.set_major_formatter(mdates.DateFormatter("%H:%M:%S"))
+
 plt.tight_layout()
 plt.show()
-