I'm trying to build countdown timer for sport events. It should be made of 3 digits (0-9) that are at least 20x7 cm and since I'm on very limited budget, I decided to use led stripes I already have (they are in 5cm segments, every segment with 3LED and resistor, 12V, 20mA).
According to http://www.arduino.cc/en/Tutorial/ShiftOut
I've create small model with 21 2mA LED and dip switch for choosing starting point for countdown (240, 120, 90 and 40 seconds). I wrote simple countdown code and it works just fine.
Since I'm planing to use 4 led stripes (2x2) for every segment of 7-seg display, I tried using schematic from http://chaokhun.kmitl.ac.th/~kswichit/Led/Led.html
(74HC595 is connected to Arduino Mega).
I'm still testing with 2mA LED and powering them with 9V battery. I've connected everything like on schematic but nothing happened, then I downloaded ULN2003A data sheet and saw that pin 8 is GND, so I connected pin 8 to GND rail on protoboard and only two LEDs powered up, turned off, and that's it.
What should I do, to make this work?
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