I am new here in the forum, and after two days of trial and error, I am completely desperate and need your help:
I have built my first PCB and use an Atmega328P. Due to my inexperience, I forgot to design the isp header to burn the bootloader to the Atmega.
Due to this fact, I soldered some wires to MISO,MOSI, SCK and Reset, and connected it to an Arduino Nano, which should work as an ISP.I used this tutorial to prepare the Nano:
Its in German, but pictures and tables should be clear.
Appropriate sketch was loaded to the Nano, and this ISP is able to burn the bootloader to another Nano. So, sketch and cabling should be ok.
But I am struggling with getting the bootloader to the stand alone Atmega on my new board. Here are the schematics and PCB layout:
At first I tried the minimal configuration as described in the tutorial, by using the board ATMega328P on a breadboard (8MHZ clock), but I got always an error during burning process. Then I tried some other configurations with regular Nano board and some other boards, and somehow, burning was working, but just for one time, and I was not able to repeat the process at the next day. In order to exclude the option of a damaged processor, I used a new PCB (I got 5 from JLCPCB) and tried again with the same result.
The Nano is still able to burn to the other Nano. So it seems there is no hardware or software problem. Even when I played around with several obviously wrong boards and parameters, I was not able to kill the Nano.
According to my assumption there is some electrical parameter close to the edge. So it works under good conditions, but more ore less accidentally.
What kind of problem should that be? I tried to bring CS to 5V, in order to avoid some disturbing actions from the MCP2515, but this does not help.
Any ideas? I need your help!!
Thanks in advance.