A Mongoose library for MAX7219, an 8-digit LED Display Driver.
The chip is straight forwardly implemented, and allows for daisy chaining
multiple devices (by tying DOUT of the first chip to DIN of the second
chip, while connecting CS, CLK, VCC and GND to all chips).
After initialization, bytes can be written to so called digits, which are
the individual lines of an 8x8 LED display, or the actual digits of a 7-segment
display.
NOTE: The MAX7219 is a 5V device, and as such level shifters are
necessary between the MOSI, SCLK and CS pins of the MCU and the pins
on the chip(s). It may work without, but it's not recommended!
Create the object with mgos_max7219_create(), and if there are multiple
devices connected, set the correct number with mgos_max7219_set_num_devices().
When you're done using the display(s), call mgos_max7219_destroy() to turn
them off and clean them up.
mgos_max7219_set_intensity() Intensity of all displays will be set,
where the argument is between 0 (very dim) to 15 (very bright).
mgos_max7219_set_mode() Setting the mode is done with a boolean
mode argument. If true is specified, all connected devices are set into what
is called Code B decoding, in which the values map internally to segments of
a 7-segment display, for example writing 0 will light up the segments needed to
draw a 0 on a 7-segment display. There are only 15 values in this system, see
the header file for details. The mode is initialized as false, in other words
do not use Code B, and now each bit on the 8-bit values correspond to one LED,
typically on an 8x8 LED display.
Writes can be performed in three ways:
mgos_max7219_write_raw() writes an 8-bit value to a certain line (digit) of
a certain device (deviceno). This will only work if the mode was set to false.
mgos_max7219_write_digit() writes a number to a certain position (digit) of
a certain device (deviceno). This will only work if the mode was set to true.
mgos_max7219_write_line() writes an array of bytes, which must be of exactly
num_devices length, to the given line (digit) of all connected displays.
#include "mgos.h"
#include "mgos_config.h"
#include "mgos_max7219.h"
const uint8_t program[] = {
0, 153, 90, 60, 24, 24, 36, 66, 5,
0, 24, 24, 255, 24, 24, 36, 66, 5,
0, 24, 24, 60, 90, 153, 36, 66, 5,
0, 24, 24, 255, 24, 24, 36, 66, 5,
};
void timer_cb(void *data) {
struct mgos_max7219 *d = (struct mgos_max7219 *)data;
static uint8_t waiting = 0;
static uint16_t position = 0;
if (!d) return;
if (waiting > 0) {
waiting--;
return;
}
waiting = program[position * 9 + 8];
LOG(LL_INFO, ("Writing program position %u, then waiting %.1f seconds", position, 0.1 * waiting));
for (int i = 0; i < 8; i++) {
mgos_max7219_write_raw(d, 0, i, program[position * 9 + i]);
mgos_max7219_write_raw(d, 1, i, ~(program[position * 9 + i]));
}
position++;
if (position == sizeof(program) / 9) position = 0;
}
enum mgos_app_init_result mgos_app_init(void) {
struct mgos_max7219 *d = NULL;
if (!(d = mgos_max7219_create(mgos_spi_get_global(), mgos_sys_config_get_max7219_cs_index())) {
LOG(LL_ERROR, ("Could not create MAX7219 display"));
return MGOS_APP_INIT_ERROR;
}
mgos_max7219_set_num_devices(d, 2);
mgos_set_timer(100, true, timer_cb, d);
return MGOS_APP_INIT_SUCCESS;
}
This project is not an official Google project. It is not supported by Google and Google specifically disclaims all warranties as to its quality, merchantability, or fitness for a particular purpose.