Cant get LCD display to work

[sixeight]

I have a cheap 1602 LCD display with i2c serial module attached. Connected it to pin 18 and 19 of a Teensy LC. Added 4k7 pullup resistors.
I also installed LiquidChrystal 1.2.1.

Tried an i2c scanner which a device at address 0x27.

But when I run the Helloworld-i2c.ino, my display just blinks the backlight and thats it. Any clues?

Here is my code:
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#define BACKLIGHT_PIN 13

LiquidCrystal_I2C lcd(0x27); // Set the LCD I2C address

//LiquidCrystal_I2C lcd(0x38, BACKLIGHT_PIN, POSITIVE); // Set the LCD I2C address


// Creat a set of new characters
const uint8_t charBitmap[][8] = {
{ 0xc, 0x12, 0x12, 0xc, 0, 0, 0, 0 },
{ 0x6, 0x9, 0x9, 0x6, 0, 0, 0, 0 },
{ 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0, 0x0 },
{ 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0, 0x0 },
{ 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0x0 },
{ 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0x0 },
{ 0x0, 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0x0 },
{ 0x0, 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0x0 }

};

void setup()
{
int charBitmapSize = (sizeof(charBitmap ) / sizeof (charBitmap[0]));

// Switch on the backlight
pinMode ( BACKLIGHT_PIN, OUTPUT );
digitalWrite ( BACKLIGHT_PIN, HIGH );

lcd.begin(16,2); // initialize the lcd

for ( int i = 0; i < charBitmapSize; i++ )
{
lcd.createChar ( i, (uint8_t *)charBitmap );
}

lcd.home (); // go home
lcd.print("Hello, ARDUINO ");
lcd.setCursor ( 0, 1 ); // go to the next line
lcd.print (" FORUM - fm ");
delay ( 1000 );
}

void loop()
{
lcd.home ();
// Do a little animation by writing to the same location
for ( int i = 0; i < 2; i++ )
{
for ( int j = 0; j < 16; j++ )
{
lcd.print (char(random(7)));
}
lcd.setCursor ( 0, 1 );
}
delay (200);
}

 

[sixeight]

I found another version that works. I think i had the wrong number for the backlight pin. Here is the working code:

#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>

#define I2C_ADDR 0x27 // <<----- Add your address here. Find it from I2C Scanner
#define BACKLIGHT_PIN 3
#define En_pin 2
#define Rw_pin 1
#define Rs_pin 0
#define D4_pin 4
#define D5_pin 5
#define D6_pin 6
#define D7_pin 7

int n = 1;

LiquidCrystal_I2C lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);

void setup()
{
lcd.begin (16,2); // <<----- My LCD was 16x2


// Switch on the backlight
lcd.setBacklightPin(BACKLIGHT_PIN,POSITIVE);
lcd.setBacklight(HIGH);
lcd.home (); // go home

lcd.print("SainSmartI2C16x2");
}

void loop()
{
// Backlight on/off every 3 seconds
lcd.setCursor (0,1); // go to start of 2nd line
lcd.print(n++,DEC);
lcd.setBacklight(LOW); // Backlight off
delay(3000);
lcd.setBacklight(HIGH); // Backlight on
delay(3000);
}

 

[MichaelMeissner]

FWIW, I have one 16x2 i2c display that only works with 5v input. So it works fine with my Arduino Uno, but with the Teensy 3.1, I need to do a level conversion of the SDA/SCL pins, and power it with 5v (from VIN).

 

[sixeight]

I power the display from the 5 volts pin. I connected the pull up resistors to the 3.3 volts connection without any further power conversion.

 

[MichaelMeissner]

Some times that works, some times it doesn't. It depends on the sensitivity of the device. In addition, if you are using a Teensy 3.0 or LC, you potentially run the risk of feeding 5v input to the i2c pins (if there is any input traffic from the display to the Teensy). The Teensy 3.1's ability to handle 5v on most pins is a help in this case.