basic working code

1 files changed, 58 insertions, 0 deletions

diff --git a/ldr-counter.py b/ldr-counter.py
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+#!/usr/bin/python
+
+# Reading an analogue sensor with  a single GPIO pin
+
+# Basic script from:
+# /www.raspberrypi-spy.co.uk/2012/08/reading-analogue-sensors-with-one-gpio-pin/
+# Author : Matt Hawkins  -- Stephen Pratt (SJP)
+# Distribution : Raspbian -- SJP Arch-arm
+# Python : 2.7 -- SJP converted to v3.5
+# GPIO   : RPi.GPIO v3.1.0a
+
+# PIN assignments:
+#   pin     Name        Connection
+#   1       +3.3V       power source
+#   7       GPIO 4      read sensor
+#   9       Ground      Ground
+
+# circuit characteristics
+#   series resistor             = 220 Ohm
+#   LDR resistance (full sun)   = 360 Ohm
+#                   'dusk'      =   3 M Ohm
+#   capactitor                  = 10 uF (quite large)
+#   max current = 3.3/580       = 5.7 mA (well within spec)
+
+import RPi.GPIO as GPIO, time
+
+# set GPIO4 as read pin
+sensorPin = 4
+# set maximum time to wait (in which case it is dark)
+maxWait = 5e6
+obsCount = 6    # number of observations
+
+# Tell the GPIO library to use Broadcom GPIO references
+GPIO.setmode(GPIO.BCM)
+
+# Define function to measure charge time
+def RCtime ():
+  timer = 0
+  # Discharge capacitor
+  GPIO.setup(sensorPin, GPIO.OUT)
+  GPIO.output(sensorPin, GPIO.LOW)
+  time.sleep(0.1)           # 100 ms
+
+  GPIO.setup(sensorPin, GPIO.IN)
+  # Count loops until voltage across
+  # capacitor reads high on GPIO
+  while (GPIO.input(sensorPin) == GPIO.LOW):
+    timer += 1
+    if timer > maxWait : return -1
+  return timer
+
+# Main program loop
+obs=list()      # an empty list
+for num in range(0, obsCount):
+    obs.append(RCtime())
+    print(obs)
+print("sum=", sum(obs))
+print("Ave time: ", sum(obs)/obsCount)        # Measure timing using GPIO4