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====== Inverted LED Display ======
<color darkorange>Apr 2017</color>
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==== I made a mistake ====
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When I designed the PCB for this project. I did what most people would do and I made the PCB the 'right way up' with 40 Way Raspberry pi header and the 7 Segment LED also the normal way up (so you can read it). Later on I realised this was a bit of a mistake, because this means the Raspberry Pi Zero Power and USB connections are now at the bottom, so you can't power this up and put it on a table :(.
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Fear not though, with some help I have edited the code so that it writes the time upside-down, so if you rotate your Raspberry Pi 180° you can read the time correctly, and still put it on the table. Below is the adjusted code.
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<color #ed1c24>Please NOTE: </color> You do <color #ed1c24>NOT</color> have to rotate the 7 Segment LED on the PCB, the code does this for you.
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{{:ntp_normal.jpg?300|}}    {{:ntp_inverted.jpg?300|}}
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Above we can see the Clock working in 'Normal' mode on the left, and in 'Inverted' mode on the right.
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==== The Python Code ====
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<sxh [py][; options for SyntaxHighlighter]>
#! /usr/bin/python
# Python Script to run a 7 Segment Common Anode LED as a clock. 
# Version 1.0
import RPi.GPIO as GPIO
import time

#Define numbering system for the IO pins Raspberry Pi
GPIO.setmode(GPIO.BCM)
 
# Define GPIO ports for the 7seg
gpioSegments =  (5,6,13,19,26,21,20,16)
# 7seg_segment_pins (11,7,4,2,1,10,5,3) +  100R inline
# Setup channels for output and set initial values
for segment in (gpioSegments):
  GPIO.setup(segment,GPIO.OUT)
  GPIO.output(segment,GPIO.HIGH)
          
# Define GPIO ports for the digits 0-3
gpioDigits = (25,24,23,18)
# Pins (12,9,8,6) select digits 0-3 respectively reading LTR on display
# Setup channels for output and set initial values
for digit in (gpioDigits):
  GPIO.setup(digit,GPIO.OUT)
  GPIO.output(digit,GPIO.LOW)

#Define flags for comtrol of Colon separator on display
colon_visible=True
colon_counter=0

#Define segment arrays for each number to be displayed
numbers = {
	'0':(0,0,1,0,1,0,0,0),
    '1':(0,1,1,1,1,1,0,1), 
    '2':(0,0,1,1,0,0,1,0), 
    '3':(0,0,1,1,0,1,0,0), 
    '4':(0,1,1,0,0,1,0,1), 
    '5':(1,0,1,0,0,1,0,0), 
    '6':(1,0,1,0,0,0,0,0), 
    '7':(0,0,1,1,1,1,0,1), 
    '8':(0,0,1,0,0,0,0,0), 
    '9':(0,0,1,0,0,1,0,0), 
    ' ':(0,0,0,0,0,0,0,0)}

#Cycle through each digit and its segments  
try:
    while True:
        time_string = str(time.ctime()[11:13]+time.ctime()[14:16]).rjust(4)
        for digit in range(4):
#select digit to display
            GPIO.output(gpioDigits[digit], 2)
#set required segments on         
            for segment in range(0,8):
                GPIO.output(gpioSegments[segment], numbers[time_string[digit]][segment]) 
#check to see if we are on segment 3 of digit 2(LTR)
                if ((digit==2) and (segment==2)):
#when colon counter gets to set value flip colon display mode between TRUE (visible) and False (NOT.visible)
					if (colon_counter<=25):
#count value not reached turn colon ON or OFF based on current setting of colon_visible
						if colon_visible==True:
							GPIO.output(13, 0)
						else:
							GPIO.output(13, 1)
#colon counter set value reached so flip colon display mode and reset colon counter
					else:
						colon_counter = 0
						colon_visible =  not colon_visible
#display all selected segments for a short time
            time.sleep(0.005)
#turn-off All segments
            for segment in range(0,8):
                GPIO.output(gpioSegments[segment],GPIO.HIGH)
#turn-off current digit selector pin
            GPIO.output(gpioDigits[digit], GPIO.LOW)
#advance colon counter
        colon_counter=colon_counter+1
finally:
  GPIO.cleanup()
</sxh>