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parking_sensor.py

+import time
+import datetime
+import sys
+import os
+import grovepi
+import math
+import json
+import traceback
+import subprocess
+import multiprocessing as mp
+from video_server import runVideo
+
+
+ranger = 4
+buzzer = 6
+
+alertThreshold = 100
+midThreshold = 50
+warningThreshold = 20
+
+grovepi.pinMode(ranger, "INPUT")
+grovepi.pinMode(buzzer, "OUTPUT")
+
+
+startBuzz = None
+buzzDelay = None
+buzzOn = False
+LCDUpdated = datetime.datetime.now().timestamp()      
+buzzDuration = 0.05
+
+
+#Read data from ultrasonic ranger
+def readDistance():
+    try:
+        distance = grovepi.ultrasonicRead(ranger)
+        return distance
+    except:
+        return None
+
+
+def setBuzzer(buzzOn):
+    buzzing = grovepi.digitalRead(buzzer)
+    # Read buzzer state, if buzz is needed and not buzzing already, then start buzzing. Turn off if buzz state is not wanted.
+    if buzzOn:
+        if not buzzing:
+            grovepi.digitalWrite(buzzer, 1)
+            buzzing = True
+    else:
+        if buzzing:
+            grovepi.digitalWrite(buzzer, 0)
+            buzzing = False
+
+#Wrapper for the buzzer
+def buzzerWrapper(distance):
+    global startBuzz, buzzDelay, buzzOn, buzzDuration
+    #Only start buzzer if in alert threshold
+    if distance and distance <= alertThreshold:
+        #Delay is equal to inverse of distance, with a minimum value
+        delay = (distance-warningThreshold)/100
+        delay = max(0.03, delay)
+        #If buzzer has not started, start it and set time.
+        if startBuzz is None:
+            setBuzzer(True)
+            startBuzz = datetime.datetime.now().timestamp()
+        #If not in delay, but are buzzing, keep buzzing until buzz duration has elapsed. 
+        elif not buzzDelay and startBuzz and datetime.datetime.now().timestamp() - startBuzz > buzzDuration:
+            if distance > warningThreshold:
+                buzzDelay = datetime.datetime.now().timestamp()
+                setBuzzer(False)
+        #If in delay, delay until the pause between delays has elapsed.
+        elif buzzDelay and datetime.datetime.now().timestamp() - buzzDelay > delay:
+            buzzDelay = None
+            startBuzz = None
+            
+    else:
+        #If not in alert threshold, make sure buzzer is off.
+        setBuzzer(False)
+
+def resetSystem():
+    #Reset the system to off state
+    grovepi.digitalWrite(buzzer, 0)
+
+
+def videoProcess():
+    queue = mp.Queue()
+    return mp.Process(target=runVideo, args=(queue,)), queue
+
+
+def exceptHandler(process, queue):
+    #Force system quit on exception
+    if queue:
+        queue.put('terminate')
+    time.sleep(1)
+    if process:
+        process.terminate()
+        process.join()
+    resetSystem()
+    exit()
+    
+if __name__ == '__main__':
+    process = None
+    try:
+        #Start the video server
+        process, queue = videoProcess()
+        process.start()
+        
+        #Initialise multiprocessing dictionary
+        manager = mp.Manager()
+        d = manager.dict()
+        d['warningThreshold'] = warningThreshold
+        d['midThreshold'] = midThreshold
+        d['alertThreshold'] = alertThreshold
+        
+        #First read of distance is None
+        readDistance()
+        while True:
+            #Event loop
+            distance = readDistance()
+            d['distance'] = distance
+            queue.put(d)   
+            buzzerWrapper(distance)
+    except KeyboardInterrupt:
+        exceptHandler(process, queue)
+    except Exception as e:
+        print(e)
+        exceptHandler(process, queue)
+