From 32e5b464c60f99ccd7705071b4c441a3e76cd2c7 Mon Sep 17 00:00:00 2001
From: Craig Oates <craig@craigoates.net>
Date: Sat, 14 Dec 2019 23:52:28 +0000
Subject: [PATCH] port over code from roaming-light project.

---
 light-meter.py | 129 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100755 light-meter.py

diff --git a/light-meter.py b/light-meter.py
new file mode 100755
index 0000000..8afea6b
--- /dev/null
+++ b/light-meter.py
@@ -0,0 +1,129 @@
+# 07_light_meter.py
+# From the code for the Electronics Starter Kit for the Raspberry Pi by MonkMakes.com
+
+#from Tkinter import *
+from tkinter import *
+import json
+import RPi.GPIO as GPIO
+import time, math
+import requests # for pushing the readings to roaming-light-api
+from datetime import datetime
+
+# Configure the Pi to use the BCM (Broadcom) pin names, rather than the pin positions
+GPIO.setmode(GPIO.BCM)
+
+# This project uses a photoresistor, a component whose resistance varies with the light falling on it.
+# To measure its resistance, the code records the time it takes for a capacitor to fill  
+# when supplied by a current passing through the resistor. The lower the resistance the faster 
+# it fills up. 
+#
+# You can think of a capacitor as a tank of electricity, and as it fills with charge, the voltage
+# across it increases. We cannot measure that voltage directly, because the Raspberry Pi
+# does not have an analog to digital convertor (ADC or analog input). However, we can time how long it
+# takes for the capacitor to fill with charge to the extent that it gets above the 1.65V or so
+# that counts as being a high digital input. 
+# 
+# For more information on this technique take a look at: 
+# learn.adafruit.com/basic-resistor-sensor-reading-on-raspberry-pi
+# The code here is based on that in the Raspberry Pi Cookbook (Recipes 12.1 to 12.3)
+
+
+# Pin a charges the capacitor through a fixed 1k resistor and the thermistor in series
+# pin b discharges the capacitor through a fixed 1k resistor 
+a_pin = 18
+b_pin = 23
+
+# empty the capacitor ready to start filling it up
+def discharge():
+    GPIO.setup(a_pin, GPIO.IN)
+    GPIO.setup(b_pin, GPIO.OUT)
+    GPIO.output(b_pin, False)
+    time.sleep(0.01) # 0.01 -- initial value
+
+# return the time taken for the voltage on the capacitor to count as a digital input HIGH
+# than means around 1.65V
+def charge_time():
+    GPIO.setup(b_pin, GPIO.IN)
+    GPIO.setup(a_pin, GPIO.OUT)
+    GPIO.output(a_pin, True)
+    t1 = time.time()
+    while not GPIO.input(b_pin):
+        pass
+    t2 = time.time()
+    return (t2 - t1) * 1000000
+
+# Take an analog readin as the time taken to charge after first discharging the capacitor
+def analog_read():
+    discharge()
+    return charge_time()
+
+# Convert the time taken to charge the cpacitor into a value of resistance
+# To reduce errors, do it 100 times and take the average.
+def read_resistance():
+    n = 20
+    total = 0;
+    for i in range(1, n):
+        total = total + analog_read()
+    reading = total / float(n)
+    resistance = reading * 6.05 - 939
+    return resistance
+
+def light_from_r(R):
+    # Log the reading to compress the range
+    return math.log(1000000.0/R) * 10.0
+
+# Gets the time and date (at the time of the reading)
+def get_timestamp():
+    return datetime.now().strftime(("%Y-%m-%d %H:%M:%S"))
+
+# Pushes the reading to roaming-light-api
+def push_reading(lvalue):
+    act = False
+    if lvalue > 20:
+        act = True
+    time = get_timestamp()
+    headers = {"content-type": "application/json"}
+#    payload = { "active": act, "light-reading": int(lvalue), "timestamp": time }
+    payload = { "reading": int(lvalue), "time": time}
+#    res = requests.post("http://192.168.1.228:5000/api/readings/add/1", data=json.dumps(payload), headers=headers)
+    res = requests.post("http://35.176.14.135/api/readings/add/1", data=json.dumps(payload), headers=headers)
+#    print(int(lvalue))
+#    print(res.status_code)
+    print(payload)
+
+# group together all of the GUI code into a class called App
+class App:
+
+    # this function gets called when the app is created
+    def __init__(self, master):
+        self.master = master
+        frame = Frame(master, bg="black")
+        frame.pack(expand=1)
+        label = Label(frame, text='Light', fg="white", bg="black", font=("Helvetica", 32))
+        label.grid(row=0)
+        self.reading_label = Label(frame, text='12.34', bg="black", fg="white", font=("Helvetica", 110))
+        self.reading_label.grid(row=1)
+        self.update_reading()
+
+    # Update the reading
+    def update_reading(self):
+        light = light_from_r(read_resistance())
+        reading_str = "{:.0f}".format(light)
+        self.reading_label.configure(text=reading_str)
+        self.master.after(200, self.update_reading)
+        push_reading(light)
+
+# Set the GUI running, give the window a title, size and position
+root = Tk()
+# Uncomment when app. is ready for deployment
+#root.attributes("-fullscreen", True)
+root.attributes("-zoomed", True)
+root.configure(background="black")
+root.wm_title('Light Meter')
+app = App(root)
+root.geometry("400x300+0+0")
+try:
+    root.mainloop()
+finally:
+    print("Cleaning up")
+    GPIO.cleanup()