how to upload sketches when digital pin 0 and 1 are in use

Arduino hardware
Arduino is an open-source electronics platform based on easy-to-use hardware and software. It'due south intended for anyone making interactive projects. Arduino senses the environment past receiving inputs from many sensors, and affects its surroundings by controlling lights, motors, and other actuators. You can tell your Arduino what to exercise by writing lawmaking in the Arduino programming language and using the Arduino development environment.
Source: http://www.arduino.cc/

Introduction: What Arduino is and why you'd want to utilize it.
Installation: Stride-by-footstep instructions for setting up the Arduino software and connecting it to an Arduino Uno, Mega2560, Duemilanove, Mega, or Diecimila.
Windows
Mac OS X
Linux (on the playground wiki)
Environment: Clarification of the Arduino evolution environment and how to change the default language.
Libraries: Using and installing Arduino libraries.
Troubleshooting: Advice on what to do if things don't work.

The Arduino Uno is a microcontroller board based on the ATmega328 (datasheet). It has 14 digital input/output pins (of which half dozen can be used equally PWM outputs), half dozen analog inputs, a sixteen MHz ceramic resonator, a USB connexion, a power jack, an ICSP header, and a reset button. Information technology contains everything needed to back up the microcontroller; simply connect it to a reckoner with a USB cable or power it with a Air conditioning-to-DC adapter or bombardment to get started.

Arduino Uno Specifications
Microcontroller – ATmega328;
Operating Voltage – 5V;
Input Voltage (recommended) – vii-12V;
Input Voltage (limits) – half-dozen-20V;
Digital I/O Pins – 14 (of which 6 provide PWM output);
Analog Input Pins – vi;
DC Electric current per I/O Pin – twoscore mA
DC Current for three.3V Pin – 50 mA;
Wink Retention – 32 KB (ATmega328) of which 0.v KB used by bootloader;
SRAM – ii KB (ATmega328);
EEPROM – 1 KB (ATmega328);
Clock Speed – 16 MHz;

Interfacing with hardware
Collection of information and software resources for interfacing Arduino cards with a wide range of hardware devices at www.arduino.cc

Programming Language reference
Online language reference for Arduino programming, using the free IDE development surround.

Programming
The Arduino Uno can exist programmed with the Arduino software (download). Select "Arduino Uno from the Tools > Board menu (according to the microcontroller on your board). For details, run into the reference and tutorials.
The ATmega328 on the Arduino Uno comes preburned with a bootloader that allows you lot to upload new code to it without the apply of an external hardware programmer.

Memory
The ATmega328 has 32 KB (with 0.5 KB used for the bootloader). It also has two KB of SRAM and 1 KB of EEPROM (which can exist read and written with the EEPROM library).

Input and Output
Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of forty mA and has an internal pull-up resistor (disconnected past default) of 20-50 kOhms. In addition, some pins take specialized functions:
Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL Serial chip.
External Interrupts: ii and iii. These pins tin can be configured to trigger an interrupt on a depression value, a ascent or falling edge, or a change in value. See the attachInterrupt() role for details.
PWM: 3, five, vi, 9, 10, and xi. Provide 8-fleck PWM output with the analogWrite() function.
SPI: x (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication using the SPI library.
LED: 13. At that place is a built-in LED continued to digital pin 13. When the pivot is Loftier value, the LED is on, when the pivot is Depression, information technology's off.
The Uno has 6 analog inputs, labeled A0 through A5, each of which provide x $.25 of resolution (i.eastward. 1024 different values). By default they measure out from ground to 5 volts, though is information technology possible to change the upper end of their range using the AREF pivot and the analogReference() function. Additionally, some pins have specialized functionality:
TWI: A4 or SDA pin and A5 or SCL pin. Back up TWI communication using the Wire library.
There are a couple of other pins on the board:
AREF. Reference voltage for the analog inputs. Used with analogReference().
Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields which block the one on the board.

Communication
The Arduino Uno has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial communication, which is bachelor on digital pins 0 (RX) and ane (TX). An ATmega16U2 on the board channels this serial communication over USB and appears equally a virtual com port to software on the computer. The '16U2 firmware uses the standard USB COM drivers, and no external driver is needed. However, on Windows, a .inf file is required. The Arduino software includes a series monitor which allows uncomplicated textual data to be sent to and from the Arduino board. The RX and TX LEDs on the board volition wink when data is beingness transmitted via the USB-to-serial bit and USB connection to the computer (but not for series communication on pins 0 and 1). A SoftwareSerial library allows for serial communication on any of the Uno's digital pins.
The ATmega328 likewise supports I2C (TWI) and SPI communication. The Arduino software includes a Wire library to simplify utilise of the I2C bus; see the documentation for details. For SPI communication, utilize the SPI library.

Power
The Arduino Uno can be powered via the USB connection or with an external ability supply. The power source is selected automatically. External (non-USB) ability can come up either from an Air conditioning-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a two.1mm heart-positive plug into the board'south power jack. Leads from a battery can be inserted in the Gnd and Vin pivot headers of the POWER connector. The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, yet, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and impairment the lath. The recommended range is 7 to 12 volts.
The power pins are as follows:
VIN. The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated ability source). You tin supply voltage through this pivot, or, if supplying voltage via the power jack, access it through this pin.
5V.This pin outputs a regulated 5V from the regulator on the board. The lath can be supplied with power either from the DC ability jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your lath. We don't advise it.
3V3. A 3.three volt supply generated by the on-lath regulator. Maximum current draw is 50 mA.
GND. Ground pins.
IOREF. This pin on the Arduino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the advisable ability source or enable voltage translators on the outputs for working with the 5V or iii.3V.

Automatic (Software) Reset
Rather than requiring a physical printing of the reset push button before an upload, the Arduino Uno is designed in a way that allows information technology to exist reset past software running on a continued reckoner. One of the hardware flow control lines (DTR) of the ATmega8U2/16U2 is connected to the reset line of the ATmega328 via a 100 nanofarad capacitor. When this line is asserted (taken low), the reset line drops long plenty to reset the chip. The Arduino software uses this capability to allow you to upload lawmaking by simply pressing the upload button in the Arduino environment. This means that the bootloader can have a shorter timeout, as the lowering of DTR tin can be well-coordinated with the starting time of the upload.
This setup has other implications. When the Uno is continued to either a computer running Mac OS X or Linux, it resets each time a connectedness is made to information technology from software (via USB). For the following half-second or and then, the bootloader is running on the Uno. While it is programmed to ignore malformed information (i.e. anything likewise an upload of new code), it will intercept the first few bytes of data sent to the lath later a connection is opened. If a sketch running on the board receives 1-time configuration or other data when it beginning starts, make sure that the software with which it communicates waits a 2nd afterwards opening the connection and earlier sending this data.
The Uno contains a trace that can be cut to disable the auto-reset. The pads on either side of the trace tin can be soldered together to re-enable information technology. It's labeled "RESET-EN". Y'all may as well be able to disable the auto-reset by connecting a 110 ohm resistor from 5V to the reset line; run into this forum thread for details.

USB Overcurrent Protection
The Arduino Uno has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. Although most computers provide their ain internal protection, the fuse provides an extra layer of protection. If more than 500 mA is practical to the USB port, the fuse volition automatically break the connection until the short or overload is removed.

Physical Characteristics
The maximum length and width of the Uno PCB are 2.7 and two.ane inches respectively, with the USB connector and power jack extending beyond the former dimension. 4 screw holes let the board to be attached to a surface or case. Note that the altitude between digital pins 7 and 8 is 160 mil (0.sixteen"), not an fifty-fifty multiple of the 100 mil spacing of the other pins.

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Source: https://haseloff.plantsci.cam.ac.uk/education/biomaker/arduino/index.html