:: Code Library and Tutorials ::
This code is not specific to any external devices. Code for that is found in InterfacingWithHardware. Here you find general use software snippets and libraries for calculations and 'internal' purposes.

Code Snippets and Utility Libraries

AVR Related
Protothreading, Timing & Millis
Input / Output
Storage
Communication
General
Math

Code Snippets and Utility Libraries.

AVR Related

Useful AVR commands for getting the job done
Interrupts
- Arduino Interrupts - comprehensive explanation of the use of timers (from uCHobby).
- How to use Interrupts in Arduino.
- Interrupts example.
- PcInt - simple pin change interrupt example.
Timer code
- Timer1 - Pwm, interrupt and other utilities for timer1.
- MsTimer2 - library to use Timer2 on milliseconds.
- Adjusting Arduino PWM Frequencies

Protothreading, Timing & Millis

Metro Lib: Implementation of recurring timed events like blinking LEDs or servo motor control
TimedAction a resource-friendly library for Timed Actions that occur every x millisecond.
DateTime library Software real time clock
EventFuse: Recurring clocked events via a count-down fuse
The Tween class for ramps (PWM fades, for instance)
millis() rollover handling: a function for detecting and handling rollover of the millis() function.
Prescaler-related utility library : easy get/set of the prescaler + alternative functions to millis() / delay()
heartbeat sketch - use an array to create an irregular blink pattern
Stopwatch: doing multiple things at the same time.

Input / Output

PWM Techniques
- SoftPWM - Software based PWM library that moves any pin between any 2 states (low, high, high impedence, or pull up)
- PWMallPins - here's how to get more PWM pins
- atmega_i2c_pwm_expander - Use an ATmega as a PWM expander, controlled by I²C
- 8-bit PCM audio (on a PC speaker)
Metrology
- Simple voltmeter class : uses the internal reference voltage (1.1V) to get an absolute voltage reading; can even be used to read own power source voltage value
- A one led voltmeter: so as to say the voltmeter of the poor
- LCD voltmeter: so as to say the voltmeter of the rich
- Capacitance Meter
- Logic Analyzer: a very simple logic analyzer. 1024 samples at 5.3 MHz
Sensor Functions
PID Control
- Arduino PID Library
Ultrasonic Sensors
- Ping: Simplify the usage of Ping))) Ultrasonic Sensors
Using multiple devices (including Arduinos!) on an I2C bus
Getting multiple Serial channels with an Arduino
Charlieplexing
- Charlieplex is a library which simplifies the coding of charlieplexed networks.
PIN register based pin toggle library DigitalToggle

Storage

RAM and EEPROM
- Tricks for using the hidden EEPROM and Flash memory
- A function for seeing how much memory (RAM) is available
- A set of functions to dynamically allocate arrays
- DB A simple database library for reading and writing to tables stored in EEPROM
- EDB An extended database library based on DB allowing for more records, larger records size, and external EEPROM storage
Read-only Flash ("PROGMEM") storage
- Mikal Hart's Flash library allows you to easily store strings, arrays, and tables in read-only memory without the hassle and complexity of learning PROGMEM programming.
- PROGMEM - top secret information too shocking to be included in the official reference section

Communication

Serial
- Streaming output: A simple way to get <<-style output with Serial/LCD/Ethernet/etc.
- SerialDebugger is a library that ebhances code readability, and debug control.
Twitter
- TwitterLibrary assists in posting your data to twitter

General

Unit Testing
- ArduinoUnit
Resource Friendly Datastructures
- Resource friendly structs that contain useful data in a small useful packet.
String Functions
- FloatToString
- FloatToString (Improved version 27/01/2009) in this thread.
- tempToAscii
- PString: A very lightweight string class that enables printing to buffer using the same code as Serial.print().
- printf() simple shell around vsnprintf() letting you use send printf style format strings over serial.
Behavior based programs
- Behavior based programs: A framework for describing control logic as Behavior classes.
Finite State Machine
- Finite State Machine Library from johnw188
- Finite State Machine Library that requires no source editing.

Math

Prime number generator
Smoothing Functions
- smooth(data, filterVal, smoothedVal) - a low-pass filter smoothing function, useful for removing sensor jitter
- digitalSmooth(data, smoothArrayName) - a digital low-pass filter smoothing function, useful for removing sensor jitter, and glitches
Mapping Functions
- autoscale - scale a variable between two ranges using linear interpolation
- fscale - a function to map a variable between two floating point ranges.
  Has a parameter to logarithmically favor either end of the output range
- smoothstep - a function to ease from one value to the next with a smooth "s" shaped logarithmic curve.
Random Functions
- randomHat() - choose every number from a "hat" before repeating
- randomWalk(stepSize) - wander between endpoints at a specified rate
Frequency Related
- Frequency Generation
  - Frequency generation using a hardware timer to drive a pin accurately or generate a periodic interrupt calling a function you supply.
  - freqout(freq, duration) - a simple frequency generator
  - Musical Algo Fun :: Making music with old PC speakers
  - Armstrong Music System - a collection of input and output abstractions to ease the development of musical instruments with the Arduino. This abstraction also allows sounds trigger remote hardware (PC or synthesizer) without additional coding.
  - Also see Interfacing with Hardware/Output/Audio
- Frequency Measurement
  - Arduino Frequency Counter
  - Pulse Width Determination