Arduino Uno post.

1 files changed, 37 insertions, 29 deletions

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