I recently started a project in which I want to control two 7-segment LED displays using two shift registers (74HC595) and my Arduino. I thought I had the basic ideas mastered, but I ran into some complications and I could use some help.
For this project, I wanted very (physically) large digits. I purchased two of these giant 6.5" 7-segment displays from Sparkfun. They are common anode.
The first thing I realized is that these displays likely need more than the 5V that the Arduino will supply. So, I'm guessing a different source will be needed. I'm hoping that a 12V battery would do it, but I'm not sure. I'm also a little uncertain what that implies for my circuit... does that mean I'm going to need a relay?
I also realized that I'm uncertain about the resistors I need here. I'm not sure if I'm reading it correctly, but the specs seem to indicate that there are 12 individual LEDs in each segment (five in the decimal point, which I probably don't even need for this).
The specs indicate 20mA forward current and forward voltage of 11.6-12.4V, but I don't understand if that's per LED, per segment, or for the whole display.
One other point - I intend to use multiplexing (or charlieplexing?) to cycle through and turn on individual segments to reduce power consumption at any one time. (I was thinking that if I did one segment per display, that means only two segments, at most, need to be lit at any one time.)
I'd really appreciate any advice here. It would be great if someone could put together the entire wiring diagram, but I'm happy to take a crack at it myself if somebody can answer some of the key questions. (i.e., power source, resistors)