How to Protect your Arduino Design (Electrically) Part 1

In this video we look at how to protect your Arduino against different forms of electrical damage and ensure your design is electrically rugged. We will be looking at parts such as current limiting resistors, zenor diodes, and schottky barrier diodes.

Building a Wireless Sensor Network with the nRF24L01 Part 5

In Part 5 of building a wireless sensor network with Arduino and the nRF24L01+ transceiver we take a look at our brand new PCB boards and look at the code for adding the DS18S20 and the STTS751 temperature sensors to the design. You can access the PCB Eagle files and the Arduino code from GitHub: https://github.com/ForceTronics/nRF24L01_Wireless_Sensor_Dev_Board

The Watchdog Timer on Arduino

In this video we take a look at the Watchdog Timer on Arduino and the three different ways to configure it. We show a simple example using the Watchdog Timer and you can find the code from the example below.

//**********************Arduino Code*******************************
#include <avr/wdt.h> //Watch dog timer functions
#include <EEPROM.h> //library for using EEPROM

// Pin 13 has an LED connected on most Arduino boards.
int led = 13;
volatile int wSetting = 1; //variable to store WDT setting, make it volatile since it will be used in ISR

void setup() {
  wdt_disable(); //Datasheet recommends disabling WDT right away in case of low probabibliy event
  pinMode(led, OUTPUT); //set up the LED pin to output
  pinMode(2,INPUT_PULLUP); //setup pin 2 for input since we will be using it with our button
  getSettings(); //start serial settings menu to choose WDT setting
  //setup the watchdog Timer based on the setting
  if(wSetting == 1) setWDT(0b01000000); //set for interrupt
  else if(wSetting == 2) setWDT(0b00001000); //set for reset
  else setWDT(0b01001000); //set for interrupt and then reset
}

void loop() {
  
  if(!digitalRead(2)) { //check if button to reset WDT was pressed
    digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
    wdt_reset(); //Reset the WDT 
  }
}

//This function gets the WDT setting from the user using Serial comm
void getSettings() {
  Serial.begin(57600);
  Serial.println("We just started up......");
  byte b; //variable to store interrupt / reset tracker
  if(EEPROM.get(10, b)) { //check if interrupt occurred before reset
    Serial.println("...and an interrupt occurred.....");
    b = 0; //reset variable
    EEPROM.put(10,b);
  }
  Serial.println("Select the WDT setting: 1 --> interrupt, 2 --> reset, 3 --> interrupt and reset");
  //wait for user to input setting selection
  while (!Serial.available()) { }
  wSetting = Serial.parseInt(); //get entry and ensure it is valid
  if(wSetting < 1 || wSetting > 3) {
      wSetting = 1;
   }
   Serial.print("WDT setting is ");
   Serial.println(wSetting);
   Serial.println();
   Serial.end(); //don't want to mix serial comm and interrupts together
}

/*
void setSleepInterval(byte timer) {
  sleep_enable(); //enable the sleep mode
  set_sleep_mode(SLEEP_MODE_PWR_DOWN); //set the type of sleep mode. Default is Idle. power down saves the most power
  ADCSRA &= ~(1<<ADEN); //Turn off ADC before going to sleep (set ADEN bit to 0). this saves even more power
  WDTCSR |= 0b00011000;    //Set the WDE bit and then clear it when set the prescaler, WDCE bit must be set if changing WDE bit   
  WDTCSR = 0b01000000 | timer; //This sets the WDT to the interval specified in the function argument
  wdt_reset(); //Reset the WDT 
  sleep_cpu(); //enter sleep mode. Next code that will be executed is the ISR when interrupt wakes Arduino from sleep
  sleep_disable(); //disable sleep mode
  ADCSRA |= (1<<ADEN); //Turn the ADC back on
}*/

//this function setups up and starts the watchdog timer
void setWDT(byte sWDT) {
   WDTCSR |= 0b00011000;
   WDTCSR = sWDT |  WDTO_2S; //Set WDT based user setting and for 2 second interval
   wdt_reset();
}


//This is the interrupt service routine for the WDT. It is called when the WDT times out and is in interrupt mode. 
//This ISR must be in your Arduino sketch or else the WDT will not work correctly
ISR (WDT_vect) 
{
  digitalWrite(led, HIGH); 
  if(wSetting == 3) {
    byte b = 1;
    EEPROM.put(10, b);
  }
  //wdt_disable();
}  // end of WDT_vect

How to Reset Your Arduino from Code

In this video we talk about how to reset your Arduino from code with no hands. You can find the schematic and code from this video below.

***************Arduino Code from Video************************************

// Pin 13 has an LED connected on most Arduino boards.
int led = 13;
//create a variable for detecting what mode you are in. If used in interrupt must be "volatile"
/*volatile*/ bool nMode = 1;

void setup() {
  pinMode(4, OUTPUT); //set up pin 4, which is connected to base of transistor
  digitalWrite(4,LOW); //set to low so transistor is off and doesn't trigger reset
  pinMode(led, OUTPUT); //set up the LED pin to output
  Serial.begin(57600); //start serial comm
  Serial.println("We just started back up"); //print quick message so we know we just went through setup code
  Serial.println();
  Serial.end(); //need to shut off serial comm because it uses interrupts
  //Create interrupt: 0 for pin 2, the name of the interrupt function or ISR, and condition to trigger interrupt 
  attachInterrupt(0, interruptFunction, CHANGE); 
}

void loop() {
    digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(400);               // wait 
    digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
    delay(400);               // wait 
  /*
  noInterrupts(); //disables interrupts
  // critical, time-sensitive code here
  interrupts();//enables interrupts
  */
}

//This is the function called when the interrupt occurs (pin 2 goes high)
//this is often referred to as the interrupt service routine or ISR
//This cannot take any input arguments or return anything
void interruptFunction() {
  digitalWrite(4,HIGH); //with this variable set to 1 the LED will blink
 //detachInterrupt(0); this function call will turn the interrupt off
}

Utilizing the Arduino ADC Internal Reference

In this video we look at the ADC internal reference in an Arduino, why / when would you use it, how to ensure you get good measurement accuracy when using it, and how to use it to check your battery voltage.

**********************Arduino Code from the video****************************
float iREF = 1.08; //internal reference cal factor

void setup() {
  // put your setup code here, to run once:
  analogReference(EXTERNAL);
  //burn some ADC readings after reference change
  for(int i=0; i<8; i++) analogRead(A0);
  Serial.begin(57600);
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(3000);
  Serial.print("Measured battery voltage is: ");
  Serial.println(fReadVcc());
  Serial.println();
}

//This function uses the known internal reference value of the 328p (~1.1V) to calculate the VCC value which comes from a battery
//This was leveraged from a great tutorial found at https://code.google.com/p/tinkerit/wiki/SecretVoltmeter?pageId=110412607001051797704
float fReadVcc() {
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  delay(3); //delay for 3 milliseconds
  ADCSRA |= _BV(ADSC); // Start ADC conversion
  while (bit_is_set(ADCSRA,ADSC)); //wait until conversion is complete
  int result = ADCL; //get first half of result
  result |= ADCH<<8; //get rest of the result
  float batVolt = (iREF / result)*1024; //Use the known iRef to calculate battery voltage
  return batVolt;
}

Building a Wireless Sensor Network with the nRF24L01 Part 4

In part 4 of Building a Wireless Sensor Network with the nRF24L01 we take a look at the design's PCB layout in Eagle software as well as cover some software and hardware updates to the design.

You can access the updated code and PCB files from GitHub: https://github.com/ForceTronics/nRF24L01_Wireless_Sensor_Dev_Board

Building a Wireless Sensor Network with the nRF24L01 Part 3

In part three we take a look at the updated hardware schematic of the router / end device design, how the router / end device settings work, and we go over the initial software of the router / end device. You can find the code from this video in GitHub at https://github.com/ForceTronics/nRF24L01_Wireless_Sensor_Dev_Board