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diff --git a/_archive/arduino-uno.md b/_archive/arduino-uno.md index 2d402ab..934e5ab 100644 --- a/_archive/arduino-uno.md +++ b/_archive/arduino-uno.md @@ -29,45 +29,53 @@ The steps that follow refer to the following pinout. ## 5V-16MHz configuration - 1. Connect pin 1 to 5V via a 10kΩ resistor. - 2. Connect a 16MHz crystal oscillator across pins 9 and 10. - 3. Connect each pin of the crystal to ground via 22pF capacitors. - 4. Connect pins 7, 20, and 21 to 5V. - 5. Connect pins 8 and 22 to ground. +Powering ATmega328P microcontrollers with 5V is the most common setup. This is +also how Arduino Uno boards are wired. -In addition to the the connections above, it's a good idea to add 0.1μF -decoupling capacitors between pins 7, 20, and 21 and ground. -[Here's](Makefile) a sample Makefile for avr-gcc and avrdude. +In this configuration, the microcontroller's pin 1 is connected to 5V via a +10kΩ resistor. Pins 9 and 10 are connected to a 16MHz crystal oscillator via +two 22pF capacitors connected to ground. The microcontroller is powered by +connecting pins 7, 20, and 21 to a 5V DC power supply. Lastly, pins 8 and 22 +are connected to ground. In addition to the these connections, which are +required, it's a good idea to add 0.1μF decoupling capacitors between pins 7, +20, and 21 and ground. + +[Here's](Makefile) a sample Makefile for compiling C programs for ATmega328P +microcontrollers using avr-gcc/avrdude toolchain. ## 3.3V-8MHz configuration -Standard ATmega328P chips are preconfigured to run at 5V. To run one at 3.3V, -we must first modify its fuses (e.g., BOD level). If the chip contains a -pre-installed bootloader that expects a 16MHz clock (such as the Arduino Uno -bootloader), it must be replaced with one that is more amenable to an 8MHz -clock. - -In the following steps, we use an Arduino Uno as an in-system programmer to -replace the embedded bootloader and modify the appropriate fuses. - - 1. Upload the 'ArduinoISP' sketch to the Arduino Uno. - 2. Wire up the ATmega328P IC as described in the previous section, while - replacing the 5V supply with a 3.3V supply and 16MHz crystal with an 8MHz - crystal. - 3. Connect the SPI ports (SCK, MISO, and MOSI) of the two MCUs. - 4. Connect the Arduino Uno's SS pin to the IC's RESET pin (pin 1). - 5. Connect the IC's V<sub>CC</sub> to a 5V supply (e.g., the Arduino Uno's 5V - pin). - 6. Burn the bootloader to the ATmega328P: - - Select 'ATmega328P (3.3V, 8MHz)' from Tools > Processor. - - Select 'Arduino as ISP' from Tools > Programmer. - - Select Tools > Burn Bootloader. +Electrical connections for running an ATmega328P at 3.3V are identical to that +of the 5V circuit. The only differences are that all the 5V connections are +replaced with a 3.3V power source and a 8MHz crystal oscillator takes the place +of the 16MHz crystal. + +However, standard ATmega328P chips are preconfigured to run at 5V. To run one +at 3.3V, we must first modify its fuses that control characteristics like the +BOD level. If a bootloader that expects a 16MHz clock (e.g., Arduino +bootloader) is pre-installed on the ATmega328P, it must be swapped with one +that accepts an 8MHz clock. To accomplish that, we need an in-system programmer +(ISP). + +Fortunately, we can turn an ordinary Arduino Uno board into an ISP by uploading +the 'ArduinoISP' sketch found in the Arduino IDE. The ISP communicates with the +microcontroller using a Serial Peripheral Interface (SPI). So, connect the SPI +port of the ATmega328P to that of the Arduino Uno, and the Uno's SS pin +to the ATmega328P's RESET pin. + +Power up the the ATmega328P by connecting its V<sub>CC</sub> to a 5V supply (we +can use Arduino Uno's 5V pin). From the Arduino IDE, select 'ATmega328P (3.3V, +8MHz)' for processor from the tools menu. Also from the tools menu, select +'Arduino as ISP' as programmer. Finally, upload the new bootloader by selecting +'Burn Bootloader' from the tools menu. The ATmega328P is now ready to run at 8MHz with a 3.3V power supply. You can upload programs to the ATmega328P as you normally would using avrdude. [Here's](3v3.Makefile) a sample Makefile with adjusted parameters (e.g., baud rate) for an 8MHz clock. +## Remarks + In both configurations, if you intend to use the ATmega328P's analog-to-digital converter with the internal 1.1V or AV<sub>cc</sub> voltage as reference, do not connect AREF (pin 21) to V<sub>cc</sub>. Refer to section 23.5.2 in the |