Max7219 difficulties
dmacq
Posts: 11
Hi There,
Apologies -- I apparently posted this to the wrong forum.
In any case, my problem seems to have been that I had two segments of the 7 segment display shorted out on my PCB board -- but for anyone else with similair difficulties -- this may be instructive.
cheers
MacQ
I'd be grateful for any insights people might have for programming
the Max7219 LED driver chip....
After several days of fairly intense effort I've managed to light 6
seven segment LEDs and get them working in a clock-like fashion
But not like clockWORK..
Specifically, I'm having trouble getting all of the segments to light
when they're supposed to.
For instance, 3, 5, 6, 8, 9 , 0, all light up fine.
but the bottom parts of 1,2,4-- do not -- for any digit
I'm basing my efforts on the code found at the Parallax site.
Why does it light some segments sometimes and not
others?
I believe I have the appropriate number of pull down resistors and
everything seems to be fitting snugly -- any thoughts?
Its infuriating to be this close and then come up short of a few lit
segments.
Cheers
MacQ
Apologies -- I apparently posted this to the wrong forum.
In any case, my problem seems to have been that I had two segments of the 7 segment display shorted out on my PCB board -- but for anyone else with similair difficulties -- this may be instructive.
cheers
MacQ
I'd be grateful for any insights people might have for programming
the Max7219 LED driver chip....
After several days of fairly intense effort I've managed to light 6
seven segment LEDs and get them working in a clock-like fashion
But not like clockWORK..
Specifically, I'm having trouble getting all of the segments to light
when they're supposed to.
For instance, 3, 5, 6, 8, 9 , 0, all light up fine.
but the bottom parts of 1,2,4-- do not -- for any digit
I'm basing my efforts on the code found at the Parallax site.
Why does it light some segments sometimes and not
others?
I believe I have the appropriate number of pull down resistors and
everything seems to be fitting snugly -- any thoughts?
Its infuriating to be this close and then come up short of a few lit
segments.
Cheers
MacQ
Comments
1. The MAX7219 controls segment current through a single resistor connect to its pin 18 (iSet) -- you shouldn't have others in your circuit.
2. Are you setting the decode register properly?
a. Do you want to have numbers only, or do you want full control of the segments?
If you·want to·display digits only, you can do this:
· SHIFTOUT DataPin, Clock, MSBFIRST, [noparse][[/noparse]$09, $FF]
This will set all digits to BCD decoding.· You also need to set your scan limit so that all digits are displayed:
· SHIFTOUT DataPin, Clock, MSBFIRST, [noparse][[/noparse]$0B, $07]
·
You may want to have a look at the document below to check your MAX7219 connections.
http://www.parallax.com/dl/docs/books/sw/exp/sw29.pdf
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Jon Williams
Applications Engineer, Parallax
Dallas Office
Post Edited (Jon Williams) : 7/26/2004 3:53:45 PM GMT