Re: Using 20x4 LCD display

> Am 22.10.2021 um 03:52 schrieb Olivier <Olivier.Nicole@cs.ait.ac.th>:
> 
> I would like to use a 20x4 LCD display attached to a Raspberry Pi
> running FreeBSd 12.2.
> 
> I can talk to the display through the I2C interface, when I send
> something the back light will turn off and on, so the link is
> established.

I use a 20x4 LCD (HD44780 type) over I2C (via PCF8574T) on a BeagleBone Black. For this, I manually transcribed one of the many Python libraries into plain C, and I wrote a minimalistic I2C glue interface in C, so it can be easily addressed.

I just put a .zip file for downloading it on my web site:

  https://obsigna.com/Downloads/LCD_20x4_over_I2C.zip

I added a Hello World test program (s. below). Perhaps you need to change the I2C device number and the I2C address in lcd.c. Here I have:

  uint8_t lcd_iicid = 1;
  uint8_t lcd_addr  = 0x27;

The Python code contained a lot of delays between various calls. This was not necessary for the BeagleBone Black, I removed this and it let me optimize the subroutines for transferring data to the display. I don’t know whether this would work on a Raspberry Pi, though.

Compile it with: cc i2c.c lcd.c hello.c -o hello
Run it with: ./hello

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>

#include "i2c.h"
#include "lcd.h"

int main(int argc, const char *argv[])
{
  lcd_begin();
  lcd_print("Hello, World!", 13);
  lcd_setCursor(0, 1);
  lcd_print("HD44780 over PCF8574", 20);
  lcd_setCursor(0, 2);
  lcd_print("If it does not work,", 20);
  lcd_setCursor(0, 3);
  lcd_print("do not ask me why.", 18);

  return 0;
}

Best regards

Rolf



Dr. Rolf Jansen
- -
Rua Reginaldo de Lima, 98
Parque São Diogo
09732-550, São Bernardo do Campo
São Paulo - Brazil

Phone:	0055-11/4317-0974
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E-Mail:	rj@obsigna.com <mailto:rj@obsigna.com>
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