MAX7219 / MAX7221 Driver - Decode sample

This sample demonstrates how to initialize the driver with one MAX7219 / MAX7221 device, configure one MAX7219 / MAX7221 device to decode digits with either Code-B or DIrect Addressing and display symbols.The sample demonstrates how to decode a digit with COde-B and another digit with Direct Addressing.

Sample 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. Configure "Code-B" and "Direct Addressing" decoding using led_driver_max7219_configure_chain_decode(). This sample configures even digits as 'COde-B' deocde and odd digits as 'Direct Addressing',
5. Display an array of symbols using led_driver_max7219_set_digits(),
6. Display symbols using led_driver_max7219_set_digit(),
7. Switch to normal mode with led_driver_max7219_set_chain_mode(),
8. 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 charactersistics,
3. A MAX7219 / MAX7221 device connected to eight seven segment displays with decimal point. The right most digit is assumed to be wired as digit '0' on the MAX7219 / MAX7221,
4. An 3-wire SPI connection (CLK, MOSI, /CS) between the MAX7219 / MAX7221 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 other:
   • Connect the ESP32 SPI lines (CLK, MOSI, /CS) to the MAX7219 / MAX7221 via a logic level shifter (for instance a TXS0108E),
   • Connect the ESP32 SPI lines (CLK, MOSI, /CS) to the MAX7219 / MAX7221 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 circuitery (for instance BSS138), diode clamps, ...

Firmware

In max7219_7221_decode.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.

Sample log output