Hi, maybe you can help shed light on a weird problem, I have a Sparkfun pro-mini running a single MAX7219 on a prototype board I had made. It has run fine, i.e. days. I built a 3rd board and all of the segments LED's were on full brightness, even though I used the same 30k ohm for Rset as the other two boards I made. The software can't put the MAX7219 to sleep, it just stays on. When the code runs, all you can see is a very slight dimming of the segments. Adjusting brightness in the code had no effect.
All of the 7219's came from Sparkfun and they appear legit. I soldered the chip in at 500F, which is less than the 300C recommended limit for 10 sec.
I've also confirmed resistance is 30k. (that red and orange can be tricky at times)
Not enough detail on what it is you're working with and if you mean your code is identical across all of them, so the only input I have now is that soldering at a lower temp but holding it to a component for 10 seconds is NOT "being safer" as it seems you're portraying it to be. 10 seconds against an iron is wayyyyyyy too long.
It is definitely installed correctly. My question has more to do with the 7219 than Arduino/code. In your experience working with the 7219 when they fail, have you ever seen them just turn all LED segments on and lose the ability to interpret the Din? Or do they tend to just shut down all together and do nothing?
My comment about the soldering temp related to the Maxim 7219 datasheet that specifies 300C maximum temp for 10 sec, and I was under that temp during install. Is it possible that it burned up? Sure. Is what I'm observing evidence of that, or a bad chip?
A MAX7219 at "off" has Seg pins LOW and Dig pins HIGH.
No one has any idea what your display is since you're having a hard time describing your setup. Segments? Are you using a number display? How many digits? Is it common cathode or common anode? Bar graph? Matrix? What? Without getting the needed information from you about what you are using, I'll venture a guess that all of whatever it is that is on, is on because you have anodes and cathodes backwards.
So you've made multiple boards, and you're certain they are physically identical?
Odds of you having all of your LEDs backwards is nil.
If you're saying you have multiple physically identical boards running identical code, but behavior is different, and you're super duper ultra certain everything was identical, then remove that MAX7219 and test it. You may have fried it with your soldering tactics.
Get an Arduino, only wire up the MAX7219 with DIN, LOAD, CLK, power/iSet, and test individual pins. Stick an LED cathode into the GND of the MAX7219, and see if it lights up when you run the anode through the Seg pins. Vice versa for Dig pins.
For a prototype board, you really would've saved some heartache by using some female headers/sockets for the ProMicro and the MAX7219.
Your max7219 looks like the genuine article, made by Maxim. There are many cheap copies around. Most users find that the copies work perfectly, as I have myself, but occasionally there can be problems
I started building a new board with sockets for everything, and was studying the schematic and realized that I had soldered all of the LED's backwards; which I confirmed by applying a power source to an LED and observing they were lighting up the wrong way.
The confusing part about it was that it actually worked for a while prior to just staying full bright so I had assumed it was all wired correctly.
Thank you all for the tip to add the noise reduction resistors.
I do have two decoupling capacitors on the 7219.
Aside from that, are there other design tips you would recommend in working with the 7219?
Does it matter which digital pins you use as inputs to the 7219 if I'm using the ledcontrol.h library? I ask because I'm not using the commonly used 11, 12, 13 SPI pins, which may be ok since I'm not using the SPI.h library. I'm considering switching back on future versions.
