Just a configured version of Optiboot 6.2 disabling the flashing led on D13 during power up.. Place the two files included so named "optiboot_atmega328_d13_led_off" into your Arduino Optiboot folder under hardware. ( Folder location is dependent on OS ) Add the following board to your boards.txt file. Code: grbl.name=Atmega328p for grbl grbl.upload.tool=avrdude grbl.upload.protocol=arduino grbl.upload.maximum_size=32256 grbl.upload.maximum_data_size=2048 grbl.upload.speed=115200 grbl.bootloader.tool=avrdude grbl.bootloader.low_fuses=0xFF grbl.bootloader.high_fuses=0xDE grbl.bootloader.extended_fuses=0x05 grbl.bootloader.unlock_bits=0x3F grbl.bootloader.lock_bits=0x0F grbl.bootloader.file=optiboot/optiboot_atmega328_d13_led_off.hex grbl.build.mcu=atmega328p grbl.build.f_cpu=16000000L grbl.build.board=AVR_UNO grbl.build.core=arduino grbl.build.variant=standard You can now burn your atmega328p bootloader with the Arduino IDE ( I used 1.6.12 ) If your running a Nano with 328p chip it will now act like a Uno. (smaller bootloader ) The main reason to use this bootloader vs a standard install of optiboot; Will be led on pin D13 is no longer going to flash at power up or reset. If you have a relay with say a spindle attached to D13 the flashing of the led could cause it to turn on before being told to do so with G-code commands. I used a Arduino as ISP ( changed heart beat delay in isp sketch from 40 to 20 ) and Arduino IDE 1.6.12. This bootloader is for Atmega328P chips. Use at your own risk. Compiled from Optiboot source code 6.2 Using the " make LED_START_FLASHES=0 atmega328 " command
That works to Not really a need for a bootloader other then using the usb for updating grbl and you can use the usbasp for that..
Well, this is a somewhat old thread, but... I don't own any Arduino boards that work. I have been using the AVR Toolchain and a USBTiny with Linux for years, burning bare ATmega chips with programs and using the bootloader space for more program space. However, I am not familiar with GRBL yet, so don't know if a Arduino shield is necessary for running a CNC router for PCBs. Or, just uploading the program to the Atmega, and building the hardware interface. Most likely it would be easier to use a ready-made solution for GRBL CNC control, but what is the fun in that? Have used bare AT328s for robot control via 305 MHz wireless with steppers and servos.
You don't need an actual Arduino UNO You DO need an Atmega328p You DO need a USB interface for serial communication. The default is 115200 baud so make sure it can do that reliably for long periods. Do NOT use a CH430 chip, an ATmega16u2 is used on the genuine UNO and works well, though older ones need the software updated) So, easy/cheap is to just buy a UNO (-: (genuine with a 16u2 USB chip)
