ATtiny85 I2C LCD problem

Other Hardware Displays
1

Hi,
I want to use an I2C 16x2 LCD with ATtiny85 MCU. I have already downloaded ATtiny Core, flashed firmware for 8MHz and everything seems to be working. I am using Arduino Nano (ATmega 328) as an ISP programmer.

Problem is the I2C. I have installed TinyWireM.h library and tried some libraries, which should work with it but nothing worked. Display is just dead. I2C is connected same as with any other MCU I have used (SDA->SDA, SCL->SCL, Vcc->Vcc, GND->GND, no resistors used)

I have also accidentally swapped Vcc and GND on the MCU which started to overheat but after connecting it right it worked again but something might have got burned... I dont really know if this is possible.

Any ideas? Thanks.

2

Which one?

I'm my opinion the best one is

3

Definitely try some 4K7 pull-up resistors on SDA & SCL pins.

1 Like
4

Yes, could be burned. But if you can still upload code at all, that's a hopeful sign.

5

Yes, exactly this one. I think that here is a problem with I2C and LCD libraries which seems to be pretty hard to find and also most of them are with a bad documentation.

6

You may parctice te following ATtiny85-I2CLCD Experiment. In this experiment, it is observed that the MCU gets resetted when the voltage at RESET/-pin goes below 2.8V which can be established theoretically by simple circuit analysis.

attiny85adc-3
attiny85adc-3862×370 17.2 KB

Figure-1:

Sketch:

#include<Wire.h>
#include<LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
#define LED 1    //PB1 = MISO pin onboard LED

void setup()
{
  Wire.begin();
  pinMode(LED, OUTPUT);
  analogReference(DEFAULT); //5.0V Vref

  //-------system reset indication-----
  for (int i = 0; i < 3; i++)
  {
    digitalWrite(LED, HIGH);
    delay(200);
    digitalWrite(LED, LOW);
    delay(200);
  }
  lcd.begin();//or lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);  //DPos (0-15), LPos (0-1)
  //----------------------
  Wire.beginTransmission(0x27);
  byte busStatus = Wire.endTransmission();
  if (busStatus != 0)
  {
     	While(true)   //error indication
	{
	   	digitalWrite(LED, HIGH);
    		delay(100);
    		digitalWrite(LED, LOW);
    		delay(100);
	}
  }
  lcd.print("I2CLCD is found!");
  delay(2000);
  lcd.clear();
}

void loop()
{
  lcd.setCursor(0, 0);
  digitalWrite(LED, HIGH);   //debug message to see MCU reset
  delay(1000);
  digitalWrite(LED, LOW);
  delay(1000);
  //------------------
  unsigned int y = analogRead(A0);
  float testVolt = (5.0 / 1023) * y;
  lcd.print(testVolt, 1);
  lcd.print(" V");
}
7

Seems that adding pull up 4k7 resistors on SDA ans SCL solved the problem! Thank you everybody for help!

8

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