Hi, I'm planning to start a project involving large 7 segment displays. The device will basically involve a user entering 1-3 digits on a keypad which will output the entered numbers to a minimum of 2 x 3-digit 7 segment displays. The first display will be 3 single digits (1 inch) and be integrated with the keypad and arduino in an enclosure. The second display will also be 3 single digits (5 inches) but will be displayed/mounted at a remote location (less than 50 ft). The large display however, will incorporate an additional port to daisy chain additional displays. All displays will be showing the same number. I plan on using ethernet cabling to connect the displays.
Now, I understand most of the projects, examples, and tutorials involving 7 segment displays and multiplexing, but I am at a complete loss of how to drive 9-12 volt segments in conjunction with shift registers. I initially planned on using 2 MAX7219s but then I realized that it only handles up to 5V leds. However, i found an interesting (and simple) schematic by yesyes that looks promising: http://www.electronicspoint.com/attachments/1624d1300495023-max7219-and-higher-voltage-led-displays-max7219-high-voltage-leds-schematic-_final.pdf.
I'm fairly competent in programming, but somewhat new to electronics. I can follow a schematic, but have no clear understanding of anything beyond resistors, capacitors, and power, so please bear with me.
My questions are:
- Is there a better/simpler/lower-cost way than this schematic?
- If I follow the schematic, does anything in the schematic change if I drive only 3 digits instead of 8? The segments i'm planning to get are: Single Hi-Red 5.0 inch CC 7-Seg LED Display Data.
- How are the resistors for R1, R10, and the 8x 2.2k ohm in the schematic calculated?
- Will there be a problem if I send 5 and 12 volt supply, ground, clock, serial data in/out, and load signals down a single cat5 cable? Is there a cable length limit?
Just to let you know, I haven't bought the components yet. I need to plan it out first and seek your guidance so I can be sure that everything will work (hardware-wise) and not blow up.
Thanks for your help. Any suggestion is appreciated.