I created a 6x6 Led matrix and wired it to max7219 Chip.
I can turn any single Led I want but sometimes it doesn't work. After some testing, I narrowed it down to a specific pattern. If I turn more than 4 led in the same column, the display shuts down. Doesn't matter which column . it can be 5 from top, or 5 from bottom, doesn't matter. As long as its more than 4, it shuts own.
I wired the display according to this :
So, what value are you using on the Iset resistor (not shown there) and reassure us you are not powering an Arduino from "Vin" or the barrel jack?
Also explain what you mean by "the display shuts down"?
Provide photos - in good light and focus - of your arrangement.
Also you need a decoupling capacitor across the power connections of that chip for it to work correctly.
Grumpy_Mike:
Also you need a decoupling capacitor across the power connections of that chip for it to work correctly.
Thank you, I read some where that i should use a 10k Resistor. I changed it to 20k like it should be and works fine now.
Paul__B:
So, what value are you using on the Iset resistor (not shown there) and reassure us you are not powering an Arduino from "Vin" or the barrel jack?Also explain what you mean by "the display shuts down"?
Provide photos - in good light and focus - of your arrangement.
Its fixed now But would it be a problem if I actually use a battery through the barrel? right now im testing things in the USB.
But would it be a problem if I actually use a battery through the barrel?
Yes.
I read some where that i should use a 10k Resistor. I changed it to 20k like it should be and works fine now
By doing that you are reducing the current you are trying to use so your original problem was an inadequate power supply. Running it off the Arduino's 5V pin is a no go.
If you want to run the circuit on batteries, I would recommend 4xAA NiMH rechargeables. These can power the max chip directly, and the Arduino, through its 5V pin.
Grumpy_Mike:
Yes.
- That is a criminal waste of battery power burning up its power.
- If it is a 9V square battery then throw it away it is useless for powering much as they don't last very long.
- The current will be too high for the internal regulator and it will overheat and at best shut down at worst burn out.
By doing that you are reducing the current you are trying to use so your original problem was an inadequate power supply. Running it off the Arduino's 5V pin is a no go.
Ok, then all I need Is to rewire the 5V and ground to a battery instead of Arduino. everything else works the same right? I have a 450mh 2s battery. is that good?
The ground of the battery still needs to be connected to ground of the Arduino. But a 2s battery has a voltage of 7.5V so it is too high to connect directly to the chip. It needs dropping down to 5V, look for a buck converter to do this for maximum battery life.
Grumpy_Mike:
The ground of the battery still needs to be connected to ground of the Arduino. But a 2s battery has a voltage of 7.5V so it is too high to connect directly to the chip. It needs dropping down to 5V, look for a buck converter to do this for maximum battery life.
what about a PDB? i have one that takes 7.4 battery and it has a 5V connection in it. if I connect the display to the 5v slot and then connect the Arduino to another 5v slot, would that work? I wanna test it but I don't want to burn anything.
PDB?
Protein Data Bank?
Python DeBugger?
Post a clickable link please.
ut would that work?
No idea because I don't know what a PDB is, therefore I don't know if the two outputs from it have a common ground or are isolated.
The display's power and the Arduino's power need to share a common ground, here is why:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html
Why not drive the Arduino and display off the same supply? I think you are getting mixed up with powering the display from the Arduino's 5V pin, with powering the Arduino with an external supply through its 5V pin.
Grumpy_Mike:
No idea because I don't know what a PDB is, therefore I don't know if the two outputs from it have a common ground or are isolated.The display's power and the Arduino's power need to share a common ground, here is why:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.htmlWhy not drive the Arduino and display off the same supply? I think you are getting mixed up with powering the display from the Arduino's 5V pin, with powering the Arduino with an external supply through its 5V pin.
PDB is power distribution board. https://www.amazon.com/gp/product/B0796PK1KB/ref=ppx_yo_dt_b_asin_title_o02_s02?ie=UTF8&psc=1
they use it to give 4 quadcopter motors equal power.
OK, a double BEC - substantial overkill, but that arguably would do the job. 
I wouldn't have thought this would be suitable at all. Using this board as a simple voltage regulator is way way over the top, if indeed it would work at all.
I repeat I would recommend a buck converter down to 5V.
OK, my mistake, didn't read it sufficiently carefully.
It is not a double 5 V "buck" regulator but a 7-15 V to 5 V "buck" regulator together with a 7-15 V to 12 V "buck-boost" regulator. Still entirely suitable, albeit clearly overkill.
Really a very useful device.
