How to Build a Simple DC Electronic Load with Arduino Part 2

In this video we look at how to make a simple DC electronic load with Arduino and some simple components. In part two 2 we add some flexible measurement capabilities.

//***************************Arduino Code*************************************************
#include <Average.h> /* * This code was used for a tutorial on how to build a simple eload with Arduino * The Tutorial can be found on the ForceTronics YouTube Channel * This code is public domain and free for anybody to use at their own risk */ //Uncomment AVGMEAS to print out avg measurement data and uncomment FASTMEAS to print fast voltage or current measur #define AVGMEAS //#define FASTMEAS //uncomment to print fast current measurements, leave commented to print fast voltage measurements //#define FASTAMP //The following variables set the eload sequence const int sValues[] = {20,50,280}; //set the DAC value for each step const unsigned long sTime[] = {350,50,15}; //set the dwell time for each step const int sNum = 3; //number of steps in the sequence, this number should match the number or items in the arrays long repeat = -1; //set the number of times the sequence repeats, -1 means infinite //The following variables control the measurement rates int measInterval = 5; //in milli seconds, fast measurement rate. This should be less than or equal to measAvgInt int measAvgInt = 1000; //this is done in milliseconds and should be a multiple of the meas interval int aCount = 0; //tracks where we are in the sequence unsigned long sStart; //trcks when a sequence step starts its timer unsigned long mStart; //tracks when a new measurement interval starts unsigned long aHours = 0; //holds amp hour value const unsigned long m2Hours = 360000; //constant value for converting mil sec to hours const float lRes = 5.08; //exact value of eload resistor --> 5.08 const float rMult = 1.51; //multiplier for resistor divider network: R1 = 5.08k and R2 = 9.98k ratio is 9.98 / (9.98 + 5.08) = .663 --> 1.51 const byte aDCVolt = A2; //ADC channel for measuring input voltage const byte aDCCurrent = A4; //ADC channel for measuring voltage across resistor Average<float> voltMeas((measAvgInt/measInterval)); //create average obect to handle voltage measurement data Average<float> currMeas((measAvgInt/measInterval)); //create average object to handle current measurement data void setup() { pinMode(A0, OUTPUT); //A0 DAC pin to output analogWriteResolution(10); //default DAC resolution is 8 bit, swith it to 10 bit (max) analogReadResolution(12); //default ADC resolution is 10 bit, change to 12 bit Serial.begin(57600); analogWrite(A0, sValues[aCount]); //Set DAC value for first step sStart = mStart = millis(); //start timer for seq and measure interval } void loop() { while(repeat > 0 || repeat < 0) { //loop controls how often sequence repeats //timer for changing sequence step if(timer(sTime[aCount],sStart)) { aCount++; //go to next sequence step if(aCount >= sNum) aCount = 0; //if at end go back to beginning analogWrite(A0, sValues[aCount]); //Set DAC value for step sStart = millis(); //reset timer } if(timer(measInterval,mStart)) { voltMeas.push(inputVolt(aDC2Volt(analogRead(aDCVolt)))); //push value into average array currMeas.push(inputCurrent(aDC2Volt(analogRead(aDCCurrent)))); //push value into average array //print input voltage value and current values #ifdef FASTMEAS #ifdef FASTAMP Serial.println(currMeas.get((currMeas.getCount() - 1))*1000); //serial print out of fast current measurements #else Serial.println(voltMeas.get((voltMeas.getCount() - 1))); //serial print out of fast voltage measurements #endif #endif mStart = millis(); //reset timer } //print out average, max / min, and amp hour measurements if(voltMeas.getCount() == (measAvgInt/measInterval)) { #ifdef AVGMEAS Serial.print("Average voltage: "); Serial.print(voltMeas.mean()); Serial.println(" V"); //get and print average voltage value float mA = currMeas.mean()*1000; //get average current value in mA Serial.print("Average current: "); Serial.print(mA); Serial.println(" mA"); //print current value Serial.print("Max voltage: "); Serial.print(voltMeas.maximum()); Serial.println(" V"); //print max and min voltage Serial.print("Min voltage: "); Serial.print(voltMeas.minimum()); Serial.println(" V"); Serial.print("Max current: "); Serial.print(currMeas.maximum()*1000); Serial.println(" mA"); //print max and min current Serial.print("Min current: "); Serial.print(currMeas.minimum()*1000); Serial.println(" mA"); float aH = ampHoursCal(measAvgInt,mA); //calculate how much amp hours of current was consumed since start if(aH < 1000) { Serial.print("Amp hours of power source: "); Serial.print(aH); Serial.println(" uAh"); } //print current in uA else { Serial.print("Amp hours of power source: "); Serial.print(aH/1000); Serial.println(" mAh"); } //print current in mA #endif voltMeas.clear(); //clear voltage measurement array currMeas.clear(); //clear current measurement array } if(repeat > 0) repeat--; //increment repeat if not infinite loop } } //timer function that runs in mill second steps. //Inputs are timer interval and timer start time bool timer(unsigned long tInterval, unsigned long tStart) { unsigned long now = millis(); //get timer value if ((now - tStart) > tInterval ) return true; //check if interval is up return false; //interval is not up } //converts raw ADC reading to voltage value based on 3.3V reference //input is 12 bit ADC value float aDC2Volt(int aDC) { return (((float)aDC/4095)*3.3); } //function converts voltage value to input voltage value based off resistor voltage divider constant //input is measured voltage float inputVolt(float aVolt) { return (rMult*aVolt); } //converts voltage measurement at load resistor to current measurement based on load resistor value //Input is measured voltage float inputCurrent(float rVolt) { return (rVolt/lRes); } //This functions calculates amp hours //amp hour = amp hour value + (amps * (mil sec / 360k) //input: measInt is measurement interval in milli sec and aVal is the measured current value in mA float ampHoursCal(int measInt, float aVal) { aHours = aHours + (aVal * ((double)measInt/m2Hours)*1000); //this converts currect measurement to mA return aHours; }