Cascading 5x max7221 Led controllers and 30x 7 segment displays for Bttf TCD

Hello guys, I have a crazy idea and I want to plant pine trees :slight_smile:

Joking aside:
I have problems with 5 Max7221 that are cascaded (wiring should be good) ESP32 d1 Mini (wroom) pins 23 DIN 28 CSK 5 CS …
if I want to control my 30 segment displays, a row of 8 lights up completely while all the others don’t do much … I had it so far as to control 24 displays more badly than right (just make them shine).

Wiring … since the 7 -seg (common cathode) DIG to the segments and SEG to Com(v+)… the best library for me so far has been LED control… but I’m also a pretty beginner at microcontroller programming… only have Experience because I learned programming years ago in my free time and have prior knowledge of electronics… came to arduino 2 months ago by chance and recently changed the IDE to platformIO…
aug ISET I run a 33 K ohm resistor and between v++ and ground on the microcontroller I still have a 10 microfarad capacitor in parallel. My problem is that I have not been able to optimally control the displays with all libraries and hope one of you old hands can help me casually … if you need more details just go to …

What supplies the +5V? The ESP32 dev board that is powered from USB or some external power supply? You might ge getting over the 500mA USB current limit. Does the voltage on the +5V pin collapse when you attempt to drive all LEDs?

yes, that could well be the problem… … 3.8 v and only 16 segments light up… what can you do?

Well if you have an external lab powersupply you can hook up that (powersupply set to 5V, connect + only the V+ pins of the MAX7721 chips, and the minus to GND, disconnect the 5V between the ESP32 and the V+ of the MAX7721 chips so it doesn’t get double powered). Same goes for a strong USB charger that can supply some amps (say between 1A and 2A at 5V). There are USB breakout boards so that can plug in normal USB cables and then grab VBUS (+5V) and GND from there.

What’s strange is that whenever I power it (USB laptop) then it’s always a gamble which and if
LDS light up, very strange…So I think it has to do with the power supply. There are also corresponding boards for a plug-in board that deliver more voltage, but I have to find out about that first. Somehow groping Gerde in the fog…
I don’t care for today anyway, but I’m playing with the idea of having an arduino board that you can attach a 12-volt adapter to… but I’d have to see if I had something like that in the basement (for sure)… But then you’d have to again first see if switching on 12 volts isn’t too much again omg :smiley:
and I would also like to thank you for your answers

That should do the trick, what do you think? →

Mean Well RS-25-5 AC/DC Power Supply Module Closed 5A 25W 5V/DC

Mean Well RS-25-5 AC/DC-Netzteilbaustein, geschlossen 5 A 25 W 5 V/DC 1 St. kaufen (

I will also see that I simulate the circuit in LTspice

It doesn’t seem particularly safe to buy when you have to attach the live 240V AC cable yourself. I’d just recommend a regular lab bench powersupply likeät-Regelbares-Schaltnetzteil/dp/B0C6K1LBDN/ orät-Elektronikwartung/dp/B0BLV8RWL6/.

Yes, those are good arguments that are definitely correct for test purposes… I bought a good quality cable with PE and of course I have to insulate it cleverly… it is not UNdangerous but in the end I would like to get it into a housing and I since I would love to have only 12 v maximum… therefore no final solution but until I’m ready a few more pines will grow :stuck_out_tongue: first i would like to know if it works properly with constant voltage and i think it is the reason alone that the usb … does not give off enough power for the amount of displays and therefore the whole setup does not work… until the stuff arrives i will take a look try LTspice… maybe that makes me smarter … so i learned thats not quit the best programm for my purposes and now i try Logisim… somehow that’s not that (the program is very outdated) promeus might be something but it’s not free… maybe someone has a good tip?

Seems to be stable so far

1 Like