Saturday, 21 February 2015

Pi-based Domestic Electricity Monitor - Part 4 - Timing intervals between flashes of the LED

The next stage in developing the electricity monitor, using the flashing LED on my domestic meter and an LDR connected to the PI, is to try to detect when the LED is on / off and log the time between flashes.

Hardware changes:

Instead of using an RC circuit, I swapped the capacitor for a 1kΩ resistor, as I am no longer interested in the analogue light level, just whether a light input is on or off. (Diag. to follow once I get Fritzing working!) [edit - Fritzing is cool]

I also added a mini voltmeter I've had kicking around for ages from a previous project, so that I could see what was happening to the voltage level on pin 23 for debugging.


This was very helpful:

I had an 'unusual' set up for testing, in that I was having a lie-in on a Saturday morning. I could control the blinds in my room from the bed, and that was enough to set Pin 23 high or low.

here's the code and output. It still needs a few tweaks but it works well enough for testing. Next job is to rebuild the hardware and attach it to the electricity meter.

#!/usr/bin/env python
# Example for edge sensing on pin 23 using a LDR and Resistor in series

#thanks to Alex Eames @ for the useful hints

#1)set pin low
#2)wait for falling edge
#3)start timer
#4)Wait for next falling edge
#5)stop timer and log or print time since last event
#6)reset and restart timer
#7) repeat
import RPi.GPIO as GPIO, time, os

#procedure to wait for transit light-->dark: 
def wait_for_dark():
    except KeyboardInterrupt:
        GPIO.cleanup()       # clean up GPIO on CTRL+C exit 

#initialise pins:     
GPIO.setup(23, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)


for i in range (0,5):
    start_time =time.time()
    elapsed_time = time.time()-start_time
    print (GPIO.input(23),elapsed_time)

GPIO.cleanup()           # clean up GPIO on normal exit        

print("Ending PRogram")  

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