Then this is not safe.

The maximum charge voltage for a lithium cell is 4.2V while USB will provide 5V. It may work for a while, it may fail in a safe state or something gets hot and burns.

You’re 100% right, I’ve lost ‘i’ somewhere in my debugging process

byte upper_byte = input_bin >> (8+i) ; byte lower_byte = (input_bin >> i) & 0x00FF;

Good idea, I’ve tried usleep after all lines, but no change…

You’re probably right, but that should only change the order of the outputs right?