7 segment display

[Guest]

hey i am building a kind of display for a running band.the display will be capable of showing the time (seconds and minutes) , the overall distance (miles and km), the speed (kmh, mph). every digit is formed of a 7 segment display. should i drive all the sevensegments as a parallel connection (4 for time, 4 for distance, 3 for speed ) or use 3 ports for each group.. and how can be the solution to this .. lots of seven segments are not easy to control ?

[Mark]

All the seven segments can be driven from the same port. The commons should be driven separately. Basically, you output your segment data, and then drive the common for a short duration. Turn off the drive and output the next displays segment data. Turn on the common drive again. You keep repeating this process. What is important is to refresh the displays at 100 times a second to prevent noticeable flicker. That would be about every 900us. Depending on what else is going on and your operating frequency, this might not allow enough time to do other tasks. If that is the case, Then you might need to drive the groups of displays separately or use some latches to hold the segment values.

[cmdrdan]

With all of those seven segment displays to control, you might want to consider a hardware approach. A MAX7219 chip will drive up to eight display digits at the cost of three I/O pins from your PIC. The 7219 has a data out pin, so that you can chain multiple display drivers without wasting more PIC I/O pins. You may be able to get a couple of them from Maxim to play with, and if you like them, you should be able to buy more at Digikey. They are on the spendy side, but so is your time spent in coding display multiplexing. Search the forum and you can find examples of 7219 drivers that others have written....

Dan