MAX 7219 LED Driver help

T&E Engineer

I have attached a stripped down version (no joystick code) of Jon's MAX7219 code written for Nuts and Volts column 70.

When I uncomment out some of the scrolling sections I can see that some LED flickering or movement is happening but what I see is all of the 35 LEDs (using LPT747 - similar to LPT757 found in Robolympics schematic) being on with different intensities as the scrolling or LED movement occurs.

I know I have it wired up correctly as per the article and the LPT747 datasheet. Is there anything I should look at just to get "something" displayed with "all" of the LEDs being on. I first thought maybe I should use a ~ somewheres in the output but I don't see where or if it needs to be used.

It is unclear if I am even using the correct "Common Cathode" 35 LED dot matrix display. Since all LEDs are on (varying intensities), there must be something correct.

Please help if you can. I bought 2 of these $20 chips each from Parallax and want to use the properly.

Thanks,

Timothy Gilmore

T&E Engineer

I found out my problem thanks to "slotcarz". The anode connections were where the cathode connections were so I swapped them. I also had to change the DATA statements and scaning from 5 columns·TO 7 rows. I still have a slight problem with scrolling but I will keep playing with it some more.

I have attached Jon's·code·(modified) for the symptoms above if anyone would·like to check it out.

PS: I would like to say that the MAX 7219 does an excellent job of displaying characters but a bit expensive at $20 each.

Thanks,

Timothy Gilmore



Post Edited (tdg8934) : 12/24/2005 8:17:48 PM GMT

Kenny Gardner

Timothy,

Head on over to Maxim's Web site and request 2 samples. That'll get you two more for free.

While there, you can buy them for $7.04. I bought 25 of them for $5.63 each. They say the lead time is 5 weeks but when I bought·mine it·only took a few days.

Jameco sells them for $9.95 or 7.59 if you buy 10 or more.

Kenny

T&E Engineer

Kenny,

Thanks for the info but Parallax even though higher in price offers great support so that to me is worth more than the hassle of Salesmen calling·me about free samples.

I do appreciate the info!

Thanks,

Timothy Gilmore