When done, paste the command it provides to the AVRDude command. Don't touch anything else (disabling reset or SPI or enabling DebugWire result in "fun" that requires a HV programmer to fix). The defaults are good, but you may want to enable EEPROM keep-on-erase and disable the clock divide-by-8 or adjust the brownout settings. So, to change the clock source, go to and select the ATMega 328P. The clock circuit is not hard to build, but it requires a few components you may not have. Note that the RX and TX need to be swapped when you connect them that is, RX to TX and TX to RX - you want the chip to RX (receive) what the adapter is TX( transmit)ing, and vice versa. You may or may not want to connect the VCC line, but it's advised to not do so if there's a lot of things connected to the chip and/or it has its own power supply. For that, connect the ground, RX, and TX pins to the adapter. Note that without the reset circuit part of the board (or again, adding your own), this still won't let you program the ATMega even with the bootloader, though. If you want to debug the chip, it's useful to also purchase a FTDI adapter or other USB-to-UART converter. You also need one to change the clock settings if you don't want to use an external crystal. This makes it a lot easier to change and debug your program outside of popping the chip out and back into the original Arduino board. These can program the ATMega 328 directly over SPI, without a bootloader (there are many instructions on the Internet search "program bare ATMega 328P with USBAsp", for instance). Since the bootloader is somewhat of a pain when the chip is on its own (since UART is picky and installing it sets the chip to use an external clock as a result), you'll want to buy an ISP programmer for the Arduino (or follow the Arduino-as-ISP sketch and instructions to make your own, which requires an Arduino with chip present, so you'd need a second to be programmed). What that does, is that it uses the UART for upload of the program while the USB chip converts the PC's messages to UART signals. On the Uno, this is done via a second Atmel chip that has USB capability, and a bootloader on the main chip. Programming a standalone chip: The Arduino's CPU is not natively designed to talk to a computer. It will also be hard to program, for a number of reasons, so you'll want to purchase a bit of fairly cheap hardware: If you remove the chip for use in a different circuit, it either needs that clock circuit added back in, or to have its fuses changed (I'll get to that in a minute). It can be used in-place if you have a clock circuit in place, or you can change the fuses (see later) and reprogram the Arduino with an ISP adapter and a clock speed of 8mhz (PlatformIO lets you do this ( and allows direct imports of an Arduino sketch) - check their docs page for the Atmel AVR plugin, but you can also look up a number of guides on how to add a board file to Arduino to tell it to use the 8mhz option for a bare chip) You may want to leave the chip on the Arduino board until you are done designing and testing your circuit. This applies even when you purchase the loose chips, since most are resold with intention of being installed in an Arduino board to replace a burned-out one, with exception of perhaps the ones from Digikey.Ĭaveats: The Arduino is designed as a prototyping board, and few things do better than it does at this task. The one tricky thing about the chip used for the official boards is that they are fused to use the faster (and more accurate) external oscillator that's mounted on the board. It's fairly easy to use a standalone Arduino chip. In a pinch if you don't have the USB converter you can either pull the chip out of an Arduino board and run wires from its D1 and D0, or hold the on-board chip in reset to allow you to borrow those serial lines without interference. You will want a USB-logical level serial adapter anyway, and once you have that you can do development on the bare chip on your board, even if you do initial testing on the Arduino. Typically chips (even those pre-flashed with a bootloader as a convenience) are cheaper than boards, so it's unclear why you would want to move the same chip off the Arduino as opposed to using another. However, you can also provide a clock crystal and its two capacitors (or a substitute resonator which often has this built in) on your external board. You cannot change the clock source over ISP unless the clock source the chip is currently expecting is operational, so if you want to change the clock selection you will want to do that before removing the chip from the Arduino. You can remove an ATMEGA from an Arduino and use it in your own board, however when used on a typical Arduino board the chip will be fused for an external crystal as a clock source, rather than the (simpler but less accurate) internal clock.
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