When using MAX7219, I am having trouble because the LED is dark

Thread Starter

mami2023

Joined Dec 26, 2023
5
[Explanatory image of wiring for LED lighting]
1703585208809.jpg

I have attached the image.

When power is connected to LED A, 20mA will flow at 100R.
This is not a problem. It shines brightly.

On the other hand, the output of the MAX7219 draws only 4mA when LED B is lit.
I control the MAX7219 with ESP32 and set it to shine the brightest.
When I measured the current of the MAX7219's ISET resistor, it was 0.28mA.
Apparently, the MAX7219 allows 100 times more current to flow through the LED than the ISET resistor current. In other words, LED B should be able to flow 28mA.
However, only 4mA flows and the light is dim.

why?
How can I get 20mA to flow to LED B?
 

Thread Starter

mami2023

Joined Dec 26, 2023
5
This is a question about lighting one LED with the MAX7219. It is not an 8x8 dot matrix.

The MAX7219 is stated to be able to flow up to 40mA per segment.

When connected as shown in the attached photo, a maximum of 40mA should be able to flow through one LED.
However, when I measure it, only 4mA flows.
If I use the <MD_MAX72xx.h> library, will only 4mA flow?

#include <MD_MAX72xx.h> library is used to light only one LED at maximum brightness.

#include <MD_MAX72xx.h>
void setup() {
Serial.begin(9600);
mx.begin();
mx.control(0, MD_MAX72XX::INTENSITY, 15);
mx.setColumn(0, 0, 0b10000000);
}

This connects pins 9 and 13 of 1088AS to MAX7219, and only the bottom right one of 1088AS lights up.
In the photo, LED B is connected to GND and pin 9, and 4mA flows.
Similarly, if LED B is connected to pins 9 and 13, 4mA will flow.

1703653339008.jpg

Even though the maximum brightness is set to 15, the intervals between pulse outputs are wide. In other words, LEDs don't shine brightly.
Why are the pulse intervals so wide?
 

Jon Chandler

Joined Jun 12, 2008
1,047
The MAX7219 is designed to multiplex 8 digits. That means the selected segments of each digit are only illuminated for ⅛ the time. The chip doesn't know if 8 digits or only 1 is connected unless you set the scan register correctly. Note the caution about having 3 or less digits illuminated.

If you're only trying to use one LED, the MAX7219 is a poor way to do so.

SmartSelect_20231226_225532_Edge.jpg
 

Thread Starter

mami2023

Joined Dec 26, 2023
5
The MAX7219 is designed to multiplex 8 digits. That means the selected segments of each digit are only illuminated for ⅛ the time. The chip doesn't know if 8 digits or only 1 is connected unless you set the scan register correctly. Note the caution about having 3 or less digits illuminated.

If you're only trying to use one LED, the MAX7219 is a poor way to do so.

View attachment 310978
Thank you for your reply.
Attach multiple LEDs to one MAX7219.
However, out of the multiple LEDs installed, only one lights up.
For example, you connect 20 LEDs, but only one lights up. Out of 20 segments, only 1 segment lights up.
The manual states that a maximum of 40mA can flow in one segment. I thought that if I turned on one LED with the library's maximum brightness setting, 20mA would flow. However, only 4mA flows. That's why I'm having trouble.
 

ericgibbs

Joined Jan 29, 2010
18,835
Hi mami,
I assume you know the ESP32 is 3.3V and the MAX is a nominal 5V,
Post a diagram showing how the power supplies connected to the modules

E
 

Thread Starter

mami2023

Joined Dec 26, 2023
5
Hi mami,
I assume you know the ESP32 is 3.3V and the MAX is a nominal 5V,
Post a diagram showing how the power supplies connected to the modules

E
Power is supplied to this ESP32 module via USB connection.
MAX7219's VCC is connected to the ESP32's VIN.
MAX7219 is supplied with 4.5V.

ESP32-DEV-CH340-USBC-003.jpg
 

Ya’akov

Joined Jan 27, 2019
9,117
Welcome to AAC.

Have you tried a loop setting the intensity register to the 16 values it supports to see if it is acting as expected (aside from the current consumption).

Have you tried other values for the ISET resistor, or a potentiometer to see if it is influencing current consumption as expected?
 
Top