I'm asking for help because I run out of ideas... (checked similar topics on the forum and nothing worked, or I didn't have tools to do it)
I want to program a circuit with ATmega328p without external oscillator. I am using Arduino Uno as a "Arduino as ISP" programmer. I wired everything (correctly - as I thought then) and managed to burn bootloader for "ATmega328 on a breadboard (8MHz internal clock)" board - and it worked fine (at least the message from avrdude was positive). But then I could not connect to the board to upload any sketch (also using Arduino as ISP). Some time later someone suggested me to add a 10k resistor between the reset pin and +5V on programmed ATmega. I did this, and tried to upload a simple sketch and it worked! But only once... (I could not connect to upload another). After that, I realized that I forgot to connect together the GND signals of both microcontrolers (it was because I have an external power source for the entire circuit so I thought I do not have to connect it - I know silly me.. :( ) After fixing this I was able to upload some sketches until once I clicked normal "Upload" button instead of "Upload using Programmer" by mistake and again I returned to the point where I cannot upload anything. Error I get all the time:
avrdude: Device signature = 0x000000
My current connections: ATMega328P Ardiono Uno SCK pin 13 MISO pin 12 MOSI pin 11 RES pin 10 GND GND +5V +5V (I decided to turn off the external source and connect directly to Arduino)
Cap 10uF on RES to GND on ArduinoUno
I checked wires a few times, even replaced them all.
Any ideas what could be wrong, or what else can I do?
The Atmega is in TQFP package and I already soldered it to the board...