Trouble using ATTINY84 with multiple I2C devices

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1

Hi everyone,

I am trying to connect an ATTINY84 to a TEA5767 radio and a LCD via PCF8574 over I2C. I have been able to successfully upload code that runs either the TEA5767 OR the LCD via PCF8574, but not both at the same time.
I just tried something different before posting. I commented out all the LCD code and removed the PCF8574 SDA and SCL wires and the radio worked. When I put the wires back in without any change to the code, there is nothing from the radio again.

Previously, I used the TEA5767 with a LCD without PCF8574, which worked fine. Now I want more pins available and changing my display to I2C seemed like an easy solution. I could switch to an Atmega board with more pins, but then I wouldn’t learn why my current approach isn’t working. Plus I would probably have the same problem.

Details:
(See the sample code below) Currently the LCD works as expected but there is nothing coming from the radio.

I am using the following boards:

TEA5767

PCF8574

Shorter version of my current code:

#include <Arduino.h>
#include <Wire.h>
#include <LCD-I2C.h>

LCD_I2C lcd(0x27, 16, 2);

void setFrequency(float frequency) { 
  frequency /= 10;
  unsigned int freqB = 4 * (frequency * 1000000 + 225000) / 32768;
  byte freqH = freqB >> 8;
  byte freqL = freqB & 0XFF;

  // printing the frequency to the LCD  
  lcd.clear(); 
  lcd.setCursor(0, 0); 
  lcd.print("F: ");
  lcd.setCursor(3, 0);
  lcd.print(frequency);

  Wire.beginTransmission(0x60);
  Wire.write(freqH);
  Wire.write(freqL);
  Wire.write(0xB0);
  Wire.write(0x10);
  Wire.write(0x00);
  Wire.endTransmission();

  delay(100);
}

void setup() {
  Wire.begin();

  lcd.begin(&Wire);
  
  lcd.display();
  lcd.backlight();
  lcd.print("LCD online!");
  delay(3000);

  setFrequency(893);
  delay(2000);
  }

void loop() {
    setFrequency(905);
    delay(3000);
    setFrequency(913);
    delay(3000);
    setFrequency(893);
    delay(3000);
}

platform.ini:

[env]
platform = atmelavr
board = attiny84
board_build.f_cpu = 1000000UL
framework = arduino
upload_protocol = custom
upload_port = /dev/ttyACM0
upload_speed = 9600
board_fuses.lfuse = 0x62
board_fuses.hfuse = 0xDF
board_fuses.efuse = 0xFF
platform_packages=
    platformio/tool-avrdude@^1.70200.0
lib_deps = 
    hasenradball/LCD-I2C@^1.0.0

[env:usbasp]
upload_flags =
    -C
    ${platformio.packages_dir}/tool-avrdude/avrdude.conf
    -p
    $BOARD_MCU
    -P
    $UPLOAD_PORT
    -b
    $UPLOAD_SPEED
    -c
    usbasp
    -B 10
upload_command = avrdude $UPLOAD_FLAGS -U flash:w:$SOURCE:i
2

Are you operating both the PCF8574 and TEA5767 at 5V or 3.3V?

3

Both are at 5v.
I just tried something a little different. I plugged it in, and once it got to the loop and started displaying the different stations on the LCD, I removed PCF8574’s SDA wire. After a moment, the radio began to respond and changed channels every 3 seconds as expected. When I plug the SDA wire back in, both the radio and LCD work as expected in the loop.
What is going on? Why does it work only after unplugging the SDA and plugging it back in?