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README.md

Comparator

A library for interfacing with the analog comparator peripheral in the megaAVR-0 series MCUs. Developed by MCUdude. The megaAVR-0 has one comparator where four positive and three negative pins are available for use. An alternative for the negative pin is to use an internally generated reference voltage instead. More useful information about the analog comparator can be found in the Microchip Application Note TB3211 and in the megaAVR-0 family data sheet.

Comparator

Class for interfacing with the built-in comparator. Use the predefined objects Comparator or Comparator0.

input_p

Variable for setting what input pin the positive input of the comparator should be connected to Accepted values:

comparator::in_p::in0; // Use positive input pin 0 (PD2) as input
comparator::in_p::in1; // Use positive input pin 1 (PD4) as input
comparator::in_p::in2; // Use positive input pin 2 (PD6) as input
comparator::in_p::in3; // Use positive input pin 3 (PD1) as input
Usage
Comparator.input_p = comparator::in_p::in0;  // Connect positive input pin 0 to the positive pin of the comparator
Default state

Comparator.input_p defaults to comparator::in_p::in0 if not specified in the user program.

input_n

Variable for setting what input pin the negative input of the comparator should be connected to Accepted values:

comparator::in_n::in0;    // Use positive input pin 0 (PD3) as input
comparator::in_n::in1;    // Use positive input pin 1 (PD5) as input
comparator::in_n::in2;    // Use positive input pin 2 (PD7) as input
comparator::in_n::dacref; // Use DACREF as input
Usage
Comparator.input_n = comparator::in_n::in0;  // Connect negative input pin 0 to the negative pin of the comparator
Default state

Comparator.input_n defaults to comparator::in_n::in0 if not specified in the user program.

reference

Variable for setting what reference voltage the DACREF should be derived from. This voltage is internally generated. Accepted values:

comparator::ref::disable;   // Do not use any reference
comparator::ref::vref_0v55; // 0.55V internal voltage
comparator::ref::vref_1v1;  // 1.1V internal voltage
comparator::ref::vref_1v5;  // 1.5V internal voltage
comparator::ref::vref_2v5;  // 2.5V internal voltage
comparator::ref::vref_4v3;  // 4.3V internal voltage
comparator::ref::vref_avcc; // Use voltage on AVCC pin
Usage
Comparator.reference = comparator::ref::vref_2v5;  // Use the internal 2.5V reference for the DACREF
Default state

Comparator.reference defaults to comparator::ref::disable if not specified in the user program.

dacref

Variable for setting the DACREF value. This voltage can be selected as the input for the negative side of the comparator. This is the formula for the DACREF output voltage:

Usage
Comparator.dacref = 127;  // Divide the reference voltage by two
Default state

Comparator.dacref defaults to 255 if not specified in the user program.

hysteresis

Variable for setting the comparator input hysteresis. Useful for eliminating "bouncing". Accepted values:

comparator::hyst::disable; // No hysteresis
comparator::hyst::small;   // 10mV hysteresis (±5mV)
comparator::hyst::medium;  // 25mV hysteresis (±12.5mV)
comparator::hyst::large;   // 50mV hysteresis (±25mV)
Usage
Comparator.hysteresis = comparator::hyst::large;  // Use 50V hysteresis
Default state

Comparator.hysteresis defaults to comparator::hyst::disable if not specified in the user program.

output

Variable for setting the comparator output, internally and/or externally. Accepted values:

comparator::out::disable;        // No output pin, signal not inverted internally
comparator::out::disable_invert; // No output pin, signal inverted internally
comparator::out::enable;         // Enable output pin (PA7), signal not inverted internally
comparator::out::invert;         // Enable output pin (PA7), signal inverted internally
comparator::out::enable_invert;  // Identical to out::invert
Usage
Comparator.output = comparator::out::enable; // Enable output pin (PA7)
Default state

Comparator.output defaults to comparator::out::disable if not specified in the user program.

init()

Method for initializing the comparator.

Usage
Comparator.init(); // Initialize comparator

start()

Method for starting the analog comparator.

Usage
Comparator.start(); // Start comparator

stop()

Method for stopping the analog comparator.

Usage
Comparator.stop(); // Stop comparator

read()

Reads the state of the analog comparator output. Works also when the physical output pin is disabled.

Usage
bool comp_state = Comparator.read(); // Read comparator

attachInterrupt()

Method for enabling analog comparator interrupt. The interrupt will trigger when the the comparator output changes. Valid arguments for the third parameters are RISING, FALLING and CHANGE.

Usage
Comparator.attachInterrupt(blinkLED, RISING); // Run the blinkLED function when the comparator output goes high

void blinkLED()
{
  digitalWrite(myLedPin, CHANGE);
}

detachInterrupt()

Method for disabling analog comparator interrupt.

Usage
Comparator.detachInterrupt(); // Disable interrupt