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/*
* Andy's Workshop NXA66 controller ATMega328p firmware
* Copyright (c) 2017 Andy Brown. http://www.andybrown.me.uk
* Please see website for licensing terms.
*/
#pragma once
namespace nxa66 {
/*
* Class to read the temperature sensor value asynchronously
*/
class Mcp9700 {
protected:
volatile static uint8_t _temperature; // temperature reading in C
public:
static void setup();
static void startReading();
static void onTimerInterrupt();
static void onCompleteInterrupt();
static uint8_t getTemperature();
};
/*
* Setup the ADC on PC0 (ADC0)
*/
inline void Mcp9700::setup() {
// ADC setup
ADMUX |= (1<<REFS0); // Vref = Avcc
ADCSRA |= (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0) | (1 << ADEN); // prescaler=128 (62.5kHz), enable
// timer setup
TCCR1A = 0;
TCCR1B = (1 << CS12) | (1 << CS10) | (1 << WGM12); // clk/1024 prescaler (7812Hz), CTC mode
TCNT1 = 0; // ensure counting starts at zero
OCR1A = 7812; // compare target = 7812 ticks (1 second ish)
TIMSK1 = (1 << OCIE1A); // enable interrupts
}
/*
* start a conversion on ADC0
*/
inline void Mcp9700::startReading() {
ADMUX &= 0xf0; // enable channel 0
ADCSRA |= (1 << ADIE); // enable interrupts
ADCSRA |= (1 << ADSC); // start conversion
}
/*
* Timer ticked at 1Hz, start a conversion
*/
inline void Mcp9700::onTimerInterrupt() {
startReading();
}
/*
* Convert the reading to temperature
*/
inline void Mcp9700::onCompleteInterrupt() {
// low must be read first. result is right aligned (ADLAR = 0)
uint8_t l = ADCL;
uint8_t h = ADCH;
// we don't need expensive floating point operations if we work in uV
// for the calculations. The sensor outputs 10,000uV/C with 500,000uV at 0C.
// the Atmega 10 bit ADC is equivalent to 4882uV per-bit with Vref = 5V
uint32_t result=l | (static_cast<uint32_t>(h) << 8);
result*=4882; // convert bits to uV
result-=500000; // subtract the zero reading (500uV)
result/=10000; // scale uV to C (10,000uV / C)
_temperature=result; // we're in the 8-bit range now
// turn the fan on/off according to the trigger thresholds
uint8_t trigger=Eeprom::Reader::fanOn();
if(result>=trigger)
FanSwitch::enable();
else {
trigger=Eeprom::Reader::fanOff();
if(result<=trigger)
FanSwitch::disable();
}
}
/*
* Read the last temperature value.
*/
inline uint8_t Mcp9700::getTemperature() {
return _temperature;
}
}