Update:

More details to answer Christ Stratton question:

My low fuse is 62: 01100010. So, according to the specifications, the internal clock is used and set at 1MHz.

I programmed the Atmega using my own test bed, a Pololu programmer (as described in the book Practical AVR Microcontrollers: Games, Gadgets, and Home Automation with the Microcontroller Used in Arduino) and avrdude (through the use of platformio). This is the command line used by platformio to flash the ROM:

/Users/[user]/.platformio/packages/tool-avrdude/avrdude -v -p atmega328p -C /Users/[user]/.platformio/packages/tool-avrdude/avrdude.conf -c avrispv2 -B 10 -e -b 115200 -P "/dev/cu.usbmodem00149121" -U flash:w:.pioenvs/pololu/firmware.hex

According to avrdude documentation, -B 10 means bitclock is set to 10us (microseconds) so a clock at speed 100Khz.

Now if I set this -B option to 1 (1Mhz), I can't program the Atmega anymore. Avrdude just timeout:

avrdude stk500v2_ReceiveMessage(): timeout

I trying to use the serial communication to work between a naked AVR Atmega328p and a computer (OS X and Linux Ubuntu).

I can program the atmega (using a pololu programmer), I make it blink a LED on a breadboard, it works fine.

I am using the Arduino libraries to facilitate the task. And they seem to work fine (using delay, digitalRead, digitalWrite, etc).

I use a USB-to-TTL CH340 chip bought on internet. The CH340 works fine, it is recognised both on Ubuntu and OS X, and the loopback test works (Put a jumper between the TX and RX line, launch screen, type something and it comes back in the terminal), so I assume the CH340 is properly recognise and works.

Then, I plug the CH340 on my board. The 5V on the + column of the breadboard, the GND to the - column. The circuit works, my LED blinks as requested. The loop function looks like this:

void setup() {
  Serial.begin(9600);
  pinMode(9, OUTPUT);
}

void loop() {
  digitalWrite(9, HIGH);   // sets the LED on
  delay(30);                     // waits for a second
  digitalWrite(9, LOW);    // sets the LED off
  delay(70);                     // waits for a second
  Serial.println("loop end");
}

As you can see, at the send of the loop I send a string on the serial line. Now, I see the blue LED blinking on the USB-to-TTL converter, so it is definitely receiving data. But when I try to connect like so:

screen /dev/cu.wchusbserialfd110 9600

on OS X, or

screen /dev/ttyUSB0 9600

on Ubuntu, nothing is displayed. I just get a black terminal.

Is the Arduino Serial works with Atmega328 ? I suppose so, as it is the same microcontroller than on the Arduino. Any idea of what I am doing wrong?

I'm trying to use the serial communication to work between a naked AVR Atmega328p and a computer (OS X and Linux Ubuntu).

I can program the atmega (using a pololu programmer), I make it blink a LED on a breadboard, it works fine.

I am using the Arduino libraries to facilitate the task. And they seem to work fine (using delay, digitalRead, digitalWrite, etc).

I use a USB-to-TTL CH340 chip bought on internet. The CH340 works fine, it is recognised both on Ubuntu and OS X, and the loopback test works (Put a jumper between the TX and RX line, launch screen, type something and it comes back in the terminal), so I assume the CH340 is properly recognise and works.

Then, I plug the CH340 on my board. The 5V on the + column of the breadboard, the GND to the - column. The circuit works, my LED blinks as requested. The loop function looks like this:

void setup() {
  Serial.begin(9600);
  pinMode(9, OUTPUT);
}

void loop() {
  digitalWrite(9, HIGH);   // sets the LED on
  delay(30);                     // waits for a second
  digitalWrite(9, LOW);    // sets the LED off
  delay(70);                     // waits for a second
  Serial.println("loop end");
}

As you can see, at the send of the loop I send a string on the serial line. Now, I see the blue LED blinking on the USB-to-TTL converter, so it is definitely receiving data. But when I try to connect like so:

screen /dev/cu.wchusbserialfd110 9600

on OS X, or

screen /dev/ttyUSB0 9600

on Ubuntu, nothing is displayed. I just get a black terminal.

Is the Arduino Serial works with Atmega328 ? I suppose so, as it is the same microcontroller than on the Arduino. Any idea of what I am doing wrong?