Arduino mini pro as ISP for Atmega329P-PU serial monitor failing

Question

After trying a lot of tutorials and manuals around the web including at least 20 solutions here on StackExchange, I don't know what to try anymore.

My goal is to write a message in the serial monitor window of the Arduino IDE from my ATMEGA328P-PU.

I have written the Arduino bootloader (tried 8 and 16MHz) to the ATMEGA and I use a 'blink' sketch as follows:

void setup()  {
 Serial.begin(9600);
 delay(100);
 pinMode(9, OUTPUT);
}

void loop()
{
 digitalWrite(9, HIGH);
 Serial.print("high");
 delay(1000);
 digitalWrite(9, LOW);
 Serial.print("low");
 delay(1000);
}

The blinking works fine, the timing looks good, not overly fast or slow.

I connect PIN3 (PCINT17, PD1, TXD) directly to the RX on the Arduino (lower red wire) and the serial monitor responds by returning nonsense like ����������.

I have checked the baud rate. I have also tested with all other baud rates in combination with and without 8Mhz and 16MHz.

I have tested the entire setup with another ATMEGA328P-PU and using an entirely other PC. Same results.

It is not possible to upload a sketch while leaving the TXD -> RX connected, so I disconnect this cable when I upload a sketch. I have also tested with only power and TXD -> RX connected.

I have also tried a few types of resistor between the TXD and RX, one of many tutorials recommended this.

This is what I am trying: http://www.instructables.com/id/Attiny-serial-monitor-using-arduino-walkthrough/

And this is my boards.txt:

##############################################################

atmega328bb.name=ATmega328 (8 MHz internal clock)

atmega328bb.upload.protocol=arduino
atmega328bb.upload.maximum_size=30720
atmega328bb.upload.speed=57600

atmega328bb.bootloader.low_fuses=0xE2
atmega328bb.bootloader.high_fuses=0xDA
atmega328bb.bootloader.extended_fuses=0x05

atmega328bb.bootloader.file=atmega/ATmegaBOOT_168_atmega328.hex
atmega328bb.bootloader.unlock_bits=0x3F
atmega328bb.bootloader.lock_bits=0x0F

atmega328bb.build.mcu=atmega328p
atmega328bb.build.f_cpu=16000000L
atmega328bb.build.core=arduino:arduino
atmega328bb.build.variant=arduino:standard


atmega328bb.bootloader.tool=arduino:avrdude
atmega328bb.upload.tool=arduino:avrdude

Answer 1

As you can see at image from linked instructables, they've connected TX pin from Tiny to TX pin on UNO through 220R resistor. This is extremely lousy idea as UNO and Tiny are both driving TX pins.

On the other side you've connected TX Output pin from Target CPU into RX Input of the Arduino ISP (pro mini). Arduino ISP returns some error responses from its TXO pin directly into the monitor. And it's at different speed I suppose, as default baud rate is 19200 in Arduino ISP sketch.

Also using internal 8MHz oscillator and: atmega328bb.build.f_cpu=16000000L means you are running at half speed as compiler and everything else expects. All speeds will be at half rate. Delays twice as long and so on.

Anyway, you can disconnect your USB to Serial converter and connect it directly to the target CPU. Or use two of them. Or just upload bootloader and get rid of ISP.

Answer 2

The thing is that you have 2 ATmegas for 1 uploader. You can't really remove the ATmega on the Pro Mini so I suggest removing the ATmega of an UNO and using the UNO without the ATmega to program your seperate ATmega. Tx to Rx and vice versa. 16MHz will work.