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| -rwxr-xr-x | ldr-counter.py | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/ldr-counter.py b/ldr-counter.py new file mode 100755 index 0000000..a96af1b --- /dev/null +++ b/ldr-counter.py @@ -0,0 +1,58 @@ +#!/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 |