View Full Version : Multiple led drivers

04-26-2006, 04:11 AM

I am driving 4x 8 digit led displays using 4x Max7219 IC's.
I also have a BS1302 chip keeping time for me.

My question is....· any ideas on how to cut down on the I/O lines required?

The above basically uses all 15 of my I/O lines.
3 for each Max and 3 for the BS1302.

I have switched a couple of the displays over to the aux I/O side·on my BS2P40.
Two·of the display's·only update occasionally and don't need to be in the main loop.

That has freed up 6, but I really need to free as many as possible on the Main I/O side.

Speaking of freeing I/O lines... any ideas on minimal I/O, 16·button matrix keyboard connections?
Found a few circuits using Pulsin and time based inputs, but they seem a bit hit and miss.


Thanks, Steve


Jon Williams
04-26-2006, 04:27 AM
You can daisy-chain the MAX7219s and the DS1302 could share the clock with them.· You might even be able to share the data line, but I would suggest separating that to keep thing simple.· That should cut things down to five lines by my count.

Jon Williams
Applications Engineer, Parallax

04-26-2006, 04:31 AM
I will try daisy chaining them tomorrow.
I will look for a circuit diagram, as I assume you would loop them using the DOUT pin on the Max's

Thanks for your time.



04-26-2006, 05:51 AM
I must be stupid....

I have looped all the clock connections
I then fed the first Max on pin 1 with the data line, then chained them in a line linking pin 28 of the Max (DOUT) to the next Max's pin 1 (DIN)
The load lines are now all linked together as well.

It appears to have gone completely screwy for some reason,
The displays no longer show the correct time etc

Another late night ahead!

Post Edited (Steve2381) : 4/25/2006 11:08:36 PM GMT