Max7219 wrong seg and dig pins

Using Arduino Displays
1

Hi
i buy a max7219 and when i connected power supply to it , the negative pin is in segX pins and the positive pins is in digX pins , thus i have reverse board and i don't know how can control it ! or if i connect parts together right or wrong !?

when i use LedControl library for driving in it using my esp8266 board and 5v external power supply there is nothing show from my code and leds are always on !

I use 4 * 1.8 inch common cathode 7 segment .

I connected boards like this together :
esp---------max7219---------7segment
D1-------------Din(1)
D2-------------CS(load)(12)
D5-------------CLK(13)
-----------------V+(19)----------------------------------5V
-----------------ISET(18)-------------------------------10Kohm resistor ----5V
-----------------segX-----------------X
-----------------dig0-----------------GND

IMG_20231029_203124_041
IMG_20231029_203124_041920×1114 117 KB

2

According to the MAX7219 datasheet, the minimum logic high input voltage (Vih) is 3.5V. The best you're going to get out of a 3.3V powered ESP8266 is 3.3V. That could be part of the problem.

1 Like
3

Is my eyes playing a trick on me or is there really a short circuit here?

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4

Your schematic like this?

image

5

You could use a HCT08 as a level converter to the MAX chip. Run it on 5V and its threshold voltages will be compatible with your processor. Check this link: Low Voltage Logic Thresholds Chart, IC Switching Levels I do not understand your word "schematic" but the part requires a common cathod Display configuration. The data sheet will confirm this see fig 2. https://www.analog.com/media/en/technical-documentation/data-sheets/MAX7219-MAX7221.pdf

1 Like
7

thanks , but nothing important , i checked it as you mention it .

8

yes , exactly ,
image

without any microcontroller, this is my schematic .

but i have positive side on digits pins . and digit pins always are high and when i connect my common cathode 7 segment turn on leds .

9

thanks, i do not attention to this part , what can i do about it ?

And main problem still exist and it's wrong functionality of max7219 on digit pins and segment pins .

10

If the LEDs are on when the digit pins are at a higher voltage than the segment pins then you must have a common anode display.
The MAX7219 needs common cathode displays.

Can you give us the part number of your displays, or a link to their datasheet?

11

max7219 is common cathode display driver ?!
image

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I tested with voltmeter and 5v+ is out from digit pin .

12

This is to do the level conversion for the SPI interface, you will still need an appropriate display. You simply wire the two inputs together and connect to the processor, the output goes to the MAX.

14

sorry , i'm totally newbie and learning ...

i tested my 7 segment, when i connect pins 2,3,4,6,7,8,9,10 to V+ and 1,5 to GND the leds turned on, i'm totally sure that my 7 segments are common cathodes .

i found this datasheet and in both cc and ca is exist :

image
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I test with voltmeter and digit pins are 5 V and the segment pins are GND , why ? is this right ?

my esp8266 not control the max7219 , maybe i need level shifter because Vih is 3.6 and output of my esp8266 is 3.3V OR max7219 wrong pins ?!

15

using "< code > " from tools bar, post your complete code.

16

If the segments each have three diodes in series, as the illustration shows, I think you are going to have trouble driving these from 5 volts. This means a solution other than an MAX7219. If you can drive these satisfactorily at 5 volts then the illustration is probably wrong.

17

Thank you all, my problem is solved with you guidence.

18

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