Hello all 
Please, I need some help with my current project, using arduino UNO
I want to connect 24 x seven segments two digit LED displays
All display will display a “solid” number from 0 to 59 and I don’t care if those numbers to change simultaneously.
For example, it’s ok if I can change a number for each display every 5-10 seconds
How can I connect all those displays to Arduino Uno?
For example - use a i2c displays and i2c multiplexors
Do you want your Arduino to drive all the 7seg displays directly doing its own multiplexing in software, or are you happy to use dedicated display driver chips ( the MAX7219 comes to mind ) that can drive 8 digits per chip.
3x MAX7219 would handle 24 displays.
How are you going to power those displays?
Can you explain this a little differently? Multiplexed display drivers show each digit in turn but do it fast enough so that it appears to our eyes that all digits are illuminated simultaneously.
Thank you both for your quick reply,
So, as I understand, I have to use displays that got i2c chip embedded and then use a i2c mutliplexter
For now I have some displays but are “bare” without any controller, I just can see 10 contacts underneath them
Also sorry for my limited knowledge, about “solid” numbers, I didn’t realize that led displays are working like you say! And it’s make sense.
Finally, I’m going to power those 24 displays using and external 5v 5A psu. Will that be enough for all those displays?
I2C is just one way of communicating the values you want to display. There's also SPI, standard UART and parallel access that can be used. It all depends on the display driver chip you choose.
Not necessarily. An I2C multiplexer is used when the chip you want to talk to doesn't have the ability to use alternate addresses and your project needs more chips than the addressing supports. Some I2C chips have 1 address input that allows selection of 2 different addresses. Others have 3 address bits allowing up to 8 different addresses.
For a 2 digit display, that is correct. There will be 7 pins - one for each segment and 1 pin will be for the decimal point. The remaining 2 are the commons for each digit. The datasheet for the display will tell you which pin is which. The datasheet for the display driver will tell you how to connect the displays to the driver.
Finally, there are common anode displays and common cathode displays. You need to make sure that your displays and driver chips are compatible.
Please give more details. How large are the displays? What is the forward voltage and current of the segments? Are they common cathode or common anode? Have you chosen or purchased them yet? If so, please post a link to the specs.
If the displays are small with a low forward voltage and current, I agree with the recommendation of 3x max7219 chips. Another recommendation could be 3x ht16k33. It may be possible to use only 2x ht16k33 chips.
Thank you very much for your very detailed reply!
I think i'll use the max7219 ic cuz seems more easy for me as a beginner
Thank you for your reply,
Im planning to use 0.28in 2 digit, seven segment display
with Forward Voltage/Segment 2.0 to 2.5 max, Current 20ma
I have the option to choose either common anode or cathode
I think HT16K33 is very advanced for me, do you think MAX7219 will be ok?
How do you want to arrange those displays? Do you intend to have 24 separate 2-digit displays that can display 00-99 - maybe spread out across a model or arranged on a scoreboard perhaps?
If you intend to group them as a pair of 2-digit displays, then you can buy these off the shelf:
They use a TM1637 driver chip. I believe that there is an Arduino library available.
You can also get 6-digit versions and these 8-digit versions:
Yes, either will be ok, they are equally advanced, but simpler than other circuits. With other circuits, you will need a very large number of Arduino pins, chips, resistors and maybe also transistors, and you will need to write your code to achieve multiplexing. With max7219 or HT16K33 you will need only a few Arduino pins, chips, resistors, no transistors and maybe a few capacitors, and the chip performs the multiplexing, making your code simpler also.
These chips were designed to make driving large numbers of LEDs more simple than other circuits. Use them.
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.