The popular MAX7219 controller is used in many 7-segment LED displays and can drive up to eight displays (for displaying eight digits):
This controller is essentially an LED driver. You are not limited to use a 7-segment LED display. You could as well drive up to 64 individual LED, i.e. to control indicator LED or drive a LED bar graph.
[!CAUTION]
This is a 5V device. Use MAX6951 if you need 3.3V operation. Typically though, even for 3.3V ESP microcontrollers, it is best to use 5V to drive LED and employ a level shifter for the control wires.
Architecture
The MAX7219 consists internally of these units:
- BCD Code-B Decoder: converts 4-bit decimal numbers in a 7-segment decimal
- Multiplex Scan Circuitry: controls 8 LED at a time in rapid succession (800Hz)
- Static RAM: stores the value displayed in each display
LED Driver
MAX7219 lets you flexibly control the connected LED:
| Item | Description |
|---|---|
| Common Cathode | LED are controlled by their anode (+) and all use the same cathode (-) |
| Brightness | digital and analog brightness control |
| Max recommended current per LED | 40mA |
| Segment Control | individual LED segment control: each LED can be controlled individually |
| LED Current | provides constant current that can be set through an external resistor |
| Max Sink Current | 500mA (62.5mA per LED) |
| Blank Mode | Can blank display to reduce energy consumption while retaining the information |
| Digits | Can be set to control between 1 (8 LED) and 8 (64 LED) 7-segment displays. |
Brightness Control
LED brightness can be controlled via current (analog) by using an external resistor, and also digitally in 16 steps.
Current Control
LED are driven by constant current. The current per LED is set by an external resistor according to this table (select the column that matches the forward voltage of the LEDs you want to drive):
| Current (mA) | 1.5V | 2.0V | 2.5V | 3.0V | 3.5V |
|---|---|---|---|---|---|
| 40 | 12.2k | 11.8k | 11k | 10.6k | 9.69k |
| 30 | 17.8k | 17.1k | 15.8k | 15k | 14k |
| 20 | 29.8k | 28k | 25.9k | 24.5k | 22.6k |
| 10 | 66.7k | 63.7k | 59.3k | 55.4k | 51.2k |
Interface
MAX7219 supports a simple 4-wire 10 MHz serial interface.
MAX7221 supports SPI, QSPI, and MICROWIRE interfaces and is slew-rate limited to reduce electromagnetic interference (EMI). Otherwise, both chips are identical.
Breakout Boards
Typically, the MAX7219 comes on a breakout board ready-to-use with 7-segment displays:
The controller and all logic is placed on the back side:
Data Sheet
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(content created Mar 28, 2024)