Arduino Microcontrollers SREEJAA SUNDARARAJU AND R. SCOTT CARSON BME 462

Parts of a sketch  void setup()  Runs at power-on and reset  Used to initialize pins and variables  void loop()  Continually runs while the microcontroller is powered  This is where work is performed

Arduino IDE  Verify  Upload  New, Open, Save  Serial Monitor

Defining a sample frequency  Max ECG frequency ~150Hz  F sample >= 2*150 Hz  F sample = 5*150 Hz = 750 Hz  We want to sample every 1.33 ms

Implementation 1 – delay()  delay(int t) or delayMicroseconds(int t)  Performs a busy wait for t time float ecg_reading = 0.0; int ecg = A0; void setup(){ Serial.begin(9600); } void loop(){ ecg_reading = analogRead(ecg); Serial.println(ecg_reading); delayMicroseconds(1333); }

Implementation 2 – Timer interrupt  ATMega328 microprocessor has 3 timers  Functionality defined by configuration registers  Can be complex if you are unfamiliar with embedded programming  88A-88PA-168A-168PA P_datasheet_Complete.pdf  TimerOne library -  A wrapper class around Timer1 to provide easy access to Timer functionality, including configuring interrupts  Interrupts –  Interrupts are used to tell the CPU a certain event has occurred and to execute a specific function known as an Interrupt Service Routine (ISR)  Interrupt events  Counter reaching a specified value  Button press  Timer expiring  This is the interesting one for us.

Timer Interrupts con’t #include void timerISR(); // Used to store analog value float ecg_reading = 0.0; int ecg = A0; // ECG analog pin volatile boolean timer_expired = false; void setup(){ Timer1.initialize(1333); Timer1.attachInterrupt(timerISR); Serial.begin(9600); } void loop(){ if(timer_expired){ noInterrupts(); ecg_reading = analogRead(ecg); Serial.println(ecg_reading); timer_expired = false; interrupts(); } void timerISR(){ timer_expired = true; }