I2c for 1602LCD display not working (raspberry pi pico) - c

Question

I am currently having an issue with trying to connect my pi pico with the I2c adapter (LCM1602 of my 1602LCD display. I tried the official example from the raspberry pi github page (It is using the c/++ SDK for pi pico, but this was unsuccessful. I can compile/load the code, but nothing is displayed. I did a I2c bus scan and found out that the I2c address is indeed 0x27. So I know the pins and address are correct. I cant find a good datasheet that gives a overview of all commands for my type of adapter. They also do this weird thing in the code where the send a one byte command in six bytes ( void lcd_send_byte(uint8_t val, int mode) ). I am not very familiar with serial communication, so I dont know if this is normal. Can anybody maybe link a good reference datasheet for a LCM1602 I2c adapter or suggest what the best thing to do is from here?
Ps: I havent tried in micropython yet, but i prefer to do this in c.
/**
* Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <stdio.h>
#include <string.h>
#include "pico/stdlib.h"
#include "hardware/i2c.h"
#include "pico/binary_info.h"
/* Example code to drive a 16x2 LCD panel via a I2C bridge chip (e.g. PCF8574)
NOTE: The panel must be capable of being driven at 3.3v NOT 5v. The Pico
GPIO (and therefor I2C) cannot be used at 5v.
You will need to use a level shifter on the I2C lines if you want to run the
board at 5v.
Connections on Raspberry Pi Pico board, other boards may vary.
GPIO 4 (pin 6)-> SDA on LCD bridge board
GPIO 5 (pin 7)-> SCL on LCD bridge board
3.3v (pin 36) -> VCC on LCD bridge board
GND (pin 38) -> GND on LCD bridge board
*/
// commands
const int LCD_CLEARDISPLAY = 0x01;
const int LCD_RETURNHOME = 0x02;
const int LCD_ENTRYMODESET = 0x04;
const int LCD_DISPLAYCONTROL = 0x08;
const int LCD_CURSORSHIFT = 0x10;
const int LCD_FUNCTIONSET = 0x20;
const int LCD_SETCGRAMADDR = 0x40;
const int LCD_SETDDRAMADDR = 0x80;
// flags for display entry mode
const int LCD_ENTRYSHIFTINCREMENT = 0x01;
const int LCD_ENTRYLEFT = 0x02;
// flags for display and cursor control
const int LCD_BLINKON = 0x01;
const int LCD_CURSORON = 0x02;
const int LCD_DISPLAYON = 0x04;
// flags for display and cursor shift
const int LCD_MOVERIGHT = 0x04;
const int LCD_DISPLAYMOVE = 0x08;
// flags for function set
const int LCD_5x10DOTS = 0x04;
const int LCD_2LINE = 0x08;
const int LCD_8BITMODE = 0x10;
// flag for backlight control
const int LCD_BACKLIGHT = 0x08;
const int LCD_ENABLE_BIT = 0x04;
// By default these LCD display drivers are on bus address 0x27
static int addr = 0x27;
// Modes for lcd_send_byte
#define LCD_CHARACTER 1
#define LCD_COMMAND 0
#define MAX_LINES 2
#define MAX_CHARS 16
/* Quick helper function for single byte transfers */
void i2c_write_byte(uint8_t val) {
#ifdef i2c_default
i2c_write_blocking(i2c_default, addr, &val, 1, false);
#endif
}
void lcd_toggle_enable(uint8_t val) {
// Toggle enable pin on LCD display
// We cannot do this too quickly or things don't work
#define DELAY_US 600
sleep_us(DELAY_US);
i2c_write_byte(val | LCD_ENABLE_BIT);
sleep_us(DELAY_US);
i2c_write_byte(val & ~LCD_ENABLE_BIT);
sleep_us(DELAY_US);
}
// The display is sent a byte as two separate nibble transfers
void lcd_send_byte(uint8_t val, int mode) {
uint8_t high = mode | (val & 0xF0) | LCD_BACKLIGHT;
uint8_t low = mode | ((val << 4) & 0xF0) | LCD_BACKLIGHT;
i2c_write_byte(high);
lcd_toggle_enable(high);
i2c_write_byte(low);
lcd_toggle_enable(low);
}
void lcd_clear(void) {
lcd_send_byte(LCD_CLEARDISPLAY, LCD_COMMAND);
}
// go to location on LCD
void lcd_set_cursor(int line, int position) {
int val = (line == 0) ? 0x80 + position : 0xC0 + position;
lcd_send_byte(val, LCD_COMMAND);
}
static void inline lcd_char(char val) {
lcd_send_byte(val, LCD_CHARACTER);
}
void lcd_string(const char *s) {
while (*s) {
lcd_char(*s++);
}
}
void lcd_init() {
lcd_send_byte(0x03, LCD_COMMAND);
lcd_send_byte(0x03, LCD_COMMAND);
lcd_send_byte(0x03, LCD_COMMAND);
lcd_send_byte(0x02, LCD_COMMAND);
lcd_send_byte(LCD_ENTRYMODESET | LCD_ENTRYLEFT, LCD_COMMAND);
lcd_send_byte(LCD_FUNCTIONSET | LCD_2LINE, LCD_COMMAND);
lcd_send_byte(LCD_DISPLAYCONTROL | LCD_DISPLAYON, LCD_COMMAND);
lcd_clear();
}
int main() {
#if !defined(i2c_default) || !defined(PICO_DEFAULT_I2C_SDA_PIN) || !defined(PICO_DEFAULT_I2C_SCL_PIN)
#warning i2c/lcd_1602_i2c example requires a board with I2C pins
#else
// This example will use I2C0 on the default SDA and SCL pins (4, 5 on a Pico)
i2c_init(i2c_default, 100 * 1000);
gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C);
gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C);
gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);
// Make the I2C pins available to picotool
bi_decl(bi_2pins_with_func(PICO_DEFAULT_I2C_SDA_PIN, PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C));
lcd_init();
static char *message[] =
{
"RP2040 by", "Raspberry Pi",
"A brand new", "microcontroller",
"Twin core M0", "Full C SDK",
"More power in", "your product",
"More beans", "than Heinz!"
};
while (1) {
for (int m = 0; m < sizeof(message) / sizeof(message[0]); m += MAX_LINES) {
for (int line = 0; line < MAX_LINES; line++) {
lcd_set_cursor(line, (MAX_CHARS / 2) - strlen(message[m + line]) / 2);
lcd_string(message[m + line]);
}
sleep_ms(2000);
lcd_clear();
}
}
return 0;
#endif
}

Answer 1

I am currently having an issue with trying to connect my pi pico with the I2c adapter (LCM1602 of my 1602LCD display
Is this the I2C adapter you're talking about ?
I can compile/load the code, but nothing is displayed
Looks like you're trying to send char *message[] as data to the display. You may want to try to send any kind off data (for exemple 0xaa,0xbb,...) to test if you can actualy communicate. If you can, try to see what's happening with an oscilloscope.
The constrast may also be changed if you think you did every thing well.
I cant find a good datasheet that gives a overview of all commands for my type of adapter
Looks like it's only an interpreter. So it doesn't have commands. It only translate the I2C data to you display.
In hope this helps you.