Hello everyone,
I have three questions regarding an LED array that is controlled with the MAX7219 and the Arduino mega 2560. I chose the resistor of 27 kOhm from the data sheet as I am using LEDs that require 20mA and 2-3V.
Now my first question:
If I drive the LEDs with the MAX7219 and use the resistor mentioned above, do I have to install 64 LEDs or can I install only 32. Would I then have to change the resistor?
Second question:
My LEDs need 20mA. If I use 32, that would be 640 mA and with 64 LEDs that would be 1280 mA. Can the Ardunio mega supply that many amps or am I missing something here? I mean, I don't have to have all the LEDs on at the same time.
Third question:
I am building the LED matrix with single LEDs on a breadboard. Do you have any tips on how I can use as few cables as possible when plugging them in? At the moment I'm still using a lot of cables and it's getting a bit confusing.
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I believe that you can use as many or as few LEDs as you like (up to the maximum supported by the chip) and the resistor value stays the same.
Definitely not. You need to find another source for your 1.2A
As already mentioned, where does 27K resistor value come from. Are you referring to the value of the Rset resistor - based upon the values in table 11 in the datasheet:
Do you have to use single LEDs? There is an 8x8 LED matrix module readily available if you didn't already know. Have a look at how the LEDs are wired within that module.
I believe that you can use as many or as few LEDs as you like (up to the maximum supported by the chip) and the resistor value stays the same.
Thank you.
Definitely not. You need to find another source for your 1.2A
As already mentioned, where does 27K resistor value come from. Are you referring to the value of the Rset resistor - based upon the values in table 11 in the datasheet:
All right. Does the 3V remain the same for the external power supply unit regardless of the number of LEDs or does it have to be changed?
Since I use different colored single LEDs, they need either 2 or 3 V. I then looked at the table of Rset in the data sheet that you listed above and selected a resistor that is between 20mA/2V and 20mA/3V. Can't I do it that way? I think the LEDs will just light up differently, right?
Do you have to use single LEDs? There is an 8x8 LED matrix module readily available if you didn't already know. Have a look at how the LEDs are wired within that module.
Thanks, but I have to use individual LEDs because I use special LEDs with different wavelengths. These are only available as single LEDs.
The 3V is the "forward voltage" of the led and varies depending on the colour, not the number of LEDs. For example red LEDs have a forward voltage of 1.8~2.0V, yellow, amber and some green LEDs are around 2.5V. Blue and white LEDs are often 3.0~3.5V.
When connected as a matrix, these voltages do not add together, but as you know, the currents add together.
The MAX7219 is a matrix driver so only a maximum of 8 LEDs will be on at a time. To use it to drive individual LEDs you will to group them in sets of 8. Here is a thread where 3 MAX7219s are used to drive strings of 60,60 and 12 LEDs to simulate an analog clock. My comments start at post 13.
Thanks.. I have aborted the idea of using the MAX7219 driver, I couldn't get it to work as desired. for some reason it was cooking my leds. I have since revamped the whole display with WS2812D leds.
I'd show some pictures on here, but can't remember how to post them..
