5 V on VCC, 3.5 V for a HIGH
VCC goes to 5V on every board, because the MAX7219 needs 4.0 to 5.5 V. The signals are another matter: the chip reads a HIGH from 3.5 V, and a 3.3 V board's HIGH is 3.3 V. It usually works and it is outside the datasheet.
Two rules, two voltages
The supply rule is simple. The MAX7219 runs from 4.0 to 5.5 V, so VCC goes to your board's 5 V pin: 5V on an Uno, an ESP32 or an ESP32-S3, VBUS on a Pico. Never 3V3. A chip under its minimum supply is not a dimmer chip; it is one the datasheet says nothing about.
The signal rule is the awkward one. The chip reads DIN, CLK and CS as HIGH from 3.5 V up. An Uno drives 5 V and clears it easily. An ESP32, an ESP32-S3 or a Pico drives 3.3 V, two tenths short.
In practice a 3.3 V board drives one of these on short wires most of the time, which is why so many projects do it. It is still outside the datasheet, and when it fails it fails as garbage on the display, not as damage.
When to add a level shifter
If the picture comes out garbled on a 3.3 V board and the wiring is right, the margin is the suspect. A level shifter on DIN, CLK and CS raises the three signals to 5 V. Nothing else needs changing: VCC was already on 5 V, and no signal comes back from the board.
When it does not work
3.3 V is under the chip's 4.0 V minimum supply. The chip is out of its specification, not at low brightness. Move VCC to 5V, or VBUS on a Pico, and keep GND where it is.
Not through this board. The MAX7219 only listens on DIN, CLK and CS, and the TK52 brings out no pin that drives a voltage back. The 5 V stays on VCC and never reaches your board's pins.
The ESP32's 3.3 V HIGH is under the chip's 3.5 V minimum, so the margin is gone. Shorten the three signal wires, keep them away from VCC, or put a level shifter on DIN, CLK and CS.
5V on an Uno, an ESP32 and an ESP32-S3 development board, from the USB port. On a Raspberry Pi Pico it is VBUS, pin 40, the USB's 5 V.
Why a TK52 talks to your board and to nothing else, and how to run two.
One board, not a chain →Edit this page — content/books/matrix-led/five-volts-and-a-high.mdx
Questions about this product
See what other owners have asked, and read their solutions.
This page covers several products. Choose yours to see the right discussions.
Discuss this article
Ask about this page. The answer stays here, on the page it belongs to, for whoever hits the same wall next.