MAX 7219 / MAX 7221 Driver for ESP32

Sample: Cascading Several Drivers

This sample demonstrates how to initialize the driver with three cascaded MAX7219 / MAX7221 devices, configure the chain for Code-B or Direct Addressing and display various symbols on all displays on the chain.

Walk through

This sample demonstrates the following capabilities:

  1. Initialize an SPI host in master mode using ESP-IDF spi_bus_initialize(),
  2. Initialize the MAX7219 / MAX7221 driver via led_driver_max7219_init(),
  3. Configure scan limit to eight digits with led_driver_max7219_configure_chain_scan_limit(),
  4. Switch between shutdown mode and normal mode with led_driver_max7219_set_chain_mode(),
  5. Switch between “Code-B” and “Direct Addressing” decoding using led_driver_max7219_configure_chain_decode(),
  6. Display symbols using led_driver_max7219_set_digit(),
  7. Shutdown the MAX7219 / MAX7221 driver and free up resources it allocated via led_driver_max7219_free().

Hardware

To make the most out of the sample, the following hardware setup is recommended:

  1. An ESP32 family device. This sample has been tested with ESP32, ESP32-S3 and ESP32-C3. Other members of the ESP32 family should also work,
  2. A power source capable of providing the MAX7219 / MAX7221 with a maximum of 6V at 500mA. See the MAX7219 / MAX7221 data sheet for electrical characteristics,
  3. Three MAX7219 / MAX7221 devices each connected to eight seven-segment displays with decimal point. The rightmost digit is assumed to be wired as digit ‘0’ on all MAX7219 / MAX7221,
  4. Connect the first MAX7219 / MAX7221 DOUT to the second MAX7219 / MAX7221 DIN and DOUT from the second MAX7219 / MAX7221 to DIN of the third MAX7219 / MAX7221 device,
  5. Connect all devices LOAD/CS and CLK. When cascading MAX7219 / MAX7221 devices, all devices share the same SPI LOAD/CS and CLK. Refer to the MAX7219 / MAX7221 data sheet for more information on cascading devices,
  6. A 3-wire SPI connection (CLK, MOSI, /CS) between the MAX7219 / MAX7221 chain and the ESP32. MAX7219 / 7221 devices cannot be reliably driven directly by 3.3V logic due to their higher than normal minimum logic high voltage (Vih) requirement of 3.5V. There are several ways to overcome this challenge. Here are a few options, among many others:
    • Connect the ESP32 SPI lines (CLK, MOSI, /CS) to the first MAX7219 / MAX7221 in the chain via a logic level shifter (for instance a TXS0108E),
    • Connect the ESP32 SPI lines (CLK, MOSI, /CS) to the first MAX7219 / MAX7221 in the chain via a 3.3V compatible logic buffer (for instance a 74HCT125 / 74AHCT125),
    • Microchip 3V Tips ‘n Tricks offers a few alternatives including connection via discrete N-Channel Logic Level Enhancement Mode FET circuitry (for instance BSS138), diode clamps, …

Firmware

In max7219_7221_cascade.c, configure CS_LOAD_PIN (/CS), CLK_PIN (CLK) and DIN_PIN (MOSI) adequately for your hardware setup:

const gpio_num_t CS_LOAD_PIN = GPIO_NUM_19;
const gpio_num_t CLK_PIN = GPIO_NUM_18;
const gpio_num_t DIN_PIN = GPIO_NUM_16;

Build and flash an ESP32 device. Ensure you have a working connection to UART as the sample emits various information via ESP_LOGxxx.

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