Hello. I'm quite new to Arduino stuff and have a question about using 8x8 dot matrix(MAX7219) with RGB LEDs.
My project is about showing numbers by using MAX7219 and LEDs.
When I tried MAX7219 alone, it worked totally fine. No problem with the codes or wiring.
Also RGB LEDs tried alone, also worked. Nothing went strange or wrong.
But after I tried MAX7219 and RGB LEDs together on the same breadboard, MAX7219 went strange, flickering and not responding properly.
I wonder what I did wrong, maybe it is fatal for MAX7219 to connect it with other devices.
What do you think about it? Should I change MAX7219 into LCD or something else?
If any of you have gone through this problem, please share your experience.
The MAX7219 can only control individual LEDs when wired in a matrix.
You can use different colours of LED, or RGB LEDs but only when you have access to both anode and cathode of all LEDs separately.
You can not use common anode or common cathode RGB LEDs.
Thank you so much with the info. But the biggest problem I have is that MAX7219 looks like it is totally damaged after I used it with RGB LEDs. I tried simple example codes but none of them worked. If it is permanently broken, it would affect the whole project so I need to know clearly if there is any possibility that MAX7219 is dead.
Yes there is a big possibility that you damaged he MAX7219.
If you post a schematic of how you wired it up with the RGB LEDs, and the simple test that used to work but now doesn’t, it should be easy to see what you might have damaged.
This is not true. It can be used with LEDs with a common cathode - I have personally used MAX7219 with 3 pin CC RG LEDs.
'The MAX7219/MAX7221 are compact, serial input/
output common-cathode display drivers that interface
microprocessors (μPs) to 7-segment numeric LED
displays of up to 8 digits, bar-graph displays, or 64 individual
LEDs.'
Yes, of course you can use the MAX7219 with RGB - common cathode or common anode - LEDs. No problem at all.
The limitation is that since each such LED requires three positions on the same row or column out of a total of eight, there are two unused positions unless you place single LEDs in those. So you can drive only sixteen RGB LEDs per MAX7219.
And since the MAX7219 has only an overall brightness control, you have only seven available colours per LED corresponding to each colour LED being either fully on or fully off. The resulting colours with two or three LEDs lit, may or may not be to your liking.
So you can only damage the MAX7219 by making some really ridiculous wiring mistake. We need to know what the OP actually did when wiring what actual sort of RGB LED in order to determine what the problem was here.
Would I be right in saying that it would be difficult to get a balanced white light like this?
The current setting resistor should, ideally, ensure each led, whether red, green or blue, gets the same current. But if you check the max7219 data sheet, the recommended values for the resistor vary according to the led forward voltage. Red LEDs have a much lower forward voltage than the green or blue in every RGB led I have come across. So I suspect it will not result in equal currents for all 3 colours and attempt to produce white will probably be quite pink.
Then you would find out how faithful is the current driver on the MAX7219 because the forward voltage affects brightness mainly with a resistive drive.
Well, you could look at table 11 on page 11 or the "Typical Operating Characteristics" on page 4 of the datasheet.
For 40 mA drive, the quoted RSET values for 2.0 V (red) and 3.5 V (just possible for blue?) are respectively 11.8 and 9.7k. It implies that the difference in current for a 10k RSET resistor would be less than 20%.
