Hi all,
I’m building a 1.8–3.6 m light sculpture using those 4-in-1 MAX7219 8×8 clone modules (the usual blue 8×32 boards, didn't know they were knockoffs until it was... too late).
Hardware:
– Raspberry Pi (SPI @ 500 kHz) (I know this is an Arduino Forum, I hope you won't mind, I decided to use an RPI for this project)
– 5 V PSU sized for worst-case current, Meanwell 5v 10A
– Power injected every 4 boards or so, all GNDs tied together
– 1000 µF + 100 nF caps at each injection
– Plan to buffer DIN/CLK/CS with a SN74AHCT125 near the first module
In testing, 8 boards behave well, but when I go further some modules near the far end glitch (clones, so not surprised).
Before I commit to 20+ boards:
– Is the SN74AHCT125 buffering approach the right way to go here?
– Would you also add Schmitt-trigger buffers (e.g. 74HC14) further down the chain, or is one buffer at the start usually enough?
– Any rules of thumb you use for max number of MAX7219 modules per chain with long wiring?
Thanks for any practical “this worked for me” examples – especially if you’ve driven more than 8 of these clone modules reliably.
Hi, thanks for replying!
Here are the details:
Processor: Raspberry Pi Zero 2 W
Language / Library: Python using the luma.led_matrix library (MAX7219 driver)
I’m trying to daisy-chain around 36 MAX7219 modules (in groups of 4 per board), powered from an external 5 V PSU with regular power injection and shared ground. Signal line is SPI0 (DIN/CLK/CS from the Pi).
The setup works reliably up to around 32 modules, but beyond that I start seeing data corruption on the last boards. I’m trying to understand whether the limitation is electrical (cable length, signal integrity, clones, need for buffering) or a library-level limit.
Okay. So presumably, you’d be looking at the library source for limits like “32”. Not something we can do here, unless one of us happens to be a Pi Zero 2 W user.
I am presuming you have done the necessary math, including reasonably conservative overages, for the current required; I would be measuring the current consumed by 4 modules, all at their brightest, to get a handle on what my power supply is faced with. Then, I’d carefully think through how the wiring distributes the current required, looking for places where you’ve drawn more than reasonable through a wire/connection, etc.
Are the “last boards” perchance farthest electrically from the power source?
Thank you!
I’m driving 32 MAX7219-based 8×8 modules using a Raspberry Pi Zero 2 W with the luma.led_matrix Python library, which doesn’t appear to impose a device limit.
Full-brightness current (for what I am doing) per 4-module board is ~0.23 A, and the whole chain draws ~0.5 A scrolling text at low brightness.
Power is injected every 4 boards, and measured voltages look acceptable-ish at idle.
However, the last boards in the chain (electrically far from injection) sometimes glitch or scramble, under load even when voltage reads ~4.8–4.9 V.
I suspect a signal-integrity issue... possibly CLK or DIN degrading over distance, and I’m considering adding a buffer (74HC14 or SN74AHCT125) between groups of boards, after reading other posts on the Arduino Forum (all posts closed as they were old).
Do you have experience stabilising long MAX7219 chains?
Anything specific to check regarding clone chips?
I’d like to see a schematic, and a photo of your installation, before I comment further. I’ve got a bit of electronics experience, but no experience driving long 7219 chains; the schematic would be helpful to identify weak points, if any.
The longest data delay between modules is 25 ns, cumulative for each stage, and the data preset time is another 25 ns. Make sure that the data at your last module are not too late for the undelayed clock signal. Better add a similar delay to the clock signal or split your long chain into multiple smaller ones.
Thanks so much for the clarification, that actually helps a lot.
You’re absolutely right about the Pi’s 3.3V logic level versus the MAX7219’s Vih requirement.
I was surprised it worked at all myself, especially over multiple modules, so your comment definitely confirms what I suspected about borderline signalling.
I’ll follow your suggestion and add proper level-shifting. One AHCT125 between the Pi and the first module, and then another AHCT125 every 4 modules to keep the signal integrity stable across the chain. That seems like the most robust way forward, especially given the total length of the run.
This explains the strange intermittent behaviour I was seeing.
Yes, anything between Vil and Vih could go either way depending the phase of the moon. However, there is still the question of the libraries capability to go over 32.