What’s running in the currently deployed prototypes

Before I dive into optimizing the code for better power management, I thought I would post the script that is actually running (hopefully!) right now in the deployed units. This code was loaded on December 15th, 2013, and I managed to buffer 3 data read cycles before each SD card write cycle with the simplest method possible – I created two more sets of variables to hold the data.  So this is my starting point for the next round of development; if you notice any serious errors here (yes, I know strings! ugh!) please feel free to leave me a comment so I can improve things. Also note that I commented out all the print statements before compiling the final sketch.

// Date, Time and Alarm functions using a DS3231 RTC connected via I2C and Wire lib by https://github.com/MrAlvin/RTClib
// based largely on Jean-Claude Wippler from JeeLab’s excellent RTC library https://github.com/jcw
// clear alarm interupt from http://forum.arduino.cc/index.php?topic=109062.0
// get temp from http://forum.arduino.cc/index.php/topic,22301.0.html which does not use the RTCLIB!
// BMA250_I2C_Sketch.pde -BMA250 Accelerometer using I2C from http://www.dsscircuits.com/accelerometer-bma250.html
// combined with internal voltage reading trick //forum.arduino.cc/index.php/topic,15629.0.html
// floats to string conversion: http://dereenigne.org/arduino/arduino-float-to-string

// free memory code tricks:
// http://playground.arduino.cc/Code/AvailableMemory#.UwUugfldUyI

// free mem stabilzes around 616 with this three cycle buffer code..
// so each extra set of buffered variables adds about 57 bytes to the ram usage

#include <SD.h>
#include <Wire.h>
#include <SPI.h> // not used here, but needed to prevent a RTClib compile error
#include <avr/sleep.h>
#include <RTClib.h>

#ifndef cbi //defs for stopping the ADC during sleep mode
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

#define DS3231_I2C_ADDRESS 104 //for the RTC temp reading function

#define BMA250 0x18
#define BW 0x08 //7.81Hz bandwith
#define GSEL 0x03 // set range 0x03 – 2g, 0x05 – 4, 0x08 – 8g, 0x0C – 16g

byte Alarmhour = 1;
byte Alarmminute = 1;
byte dummyRegister;
//volatile int state = LOW;
volatile boolean clockInterrupt = false;
byte SampleInterval = 30; // power-down time in minutes before interupt triggers next sample

byte tMSB, tLSB; //for the RTC temp reading function
float temp3231;

const byte chipSelect = 10; //sd card chip select

uint8_t dataArray[16]; //variables for accellerometer reading – why is the temp a float value?
int8_t BMAtemp; //Ok so this thing is an interger
float BMAtempfloat;
int x,y,z;

String BMAdata; //for passing back data from bma read function
String BMAdata1;
String BMAdata2 = “0000,0000,0000,0000”;
String BMAdata3 = “0000,0000,0000,0000”;
char TimeStampbuffer1[ ]= “0000/00/00,00:00:00, “;
char TimeStampbuffer2[ ]= “0000/00/00,00:00:00, “;
char TimeStampbuffer3[ ]= “0000/00/00,00:00:00, “;
float Temp3231a =0.0;
float Temp3231b =0.0;
float Temp3231c =0.0;
int Vcc1=0; //the supply voltage via 1.1 internal and gap
int Vcc2=0;
int Vcc3=0;
byte cycle=1;

int ledpin = 13; //led indicator pin not used in this code

void setup () {

digitalWrite(INTERRUPT_PIN, HIGH);//pull up the interrupt pin
pinMode(13, OUTPUT); // initialize the LED pin as an output.
digitalWrite(13, HIGH); // turn the LED on to warn against SD card removal

//RTC.adjust(DateTime(__DATE__, __TIME__)); //set the time with code compile time only run this once!
clearClockTrigger(); //stops RTC from holding the interrupt low if system reset
// time for next alarm
DateTime now = RTC.now();
Alarmhour = now.hour();
Alarmminute = now.minute()+ SampleInterval ;
if (Alarmminute > 59) { //error catch – if Alarmminute=60 the interrupt never triggers due to rollover
Alarmminute = 0; Alarmhour = Alarmhour+1; if (Alarmhour > 23) {Alarmhour =0;}

initializeBMA(); //initialize the accelerometer – do I have to do this on every wake cycle?

//get the SD card ready
pinMode(chipSelect, OUTPUT); //make sure that the default chip select pin is set to output, even if you don’t use it
//Serial.print(F(“Initializing SD card…”));
if (!SD.begin(chipSelect)) { // see if the card is present and can be initialized:
Serial.println(F(“Card failed, or not present”)); // don’t do anything more:
//Serial.println(F(“card initialized.”));
File dataFile = SD.open(“datalog.txt”, FILE_WRITE); //PRINT THE DATA FILE HEADER
if (dataFile) { // if the file is available, write to it:
dataFile.println(F(“YYYY/MM/DD HH:MM:SS, Vcc(mV), X = , Y = , Z = , BMATemp (C) , RTC temp (C)”));
else { //if the file isn’t open, pop up an error:
Serial.println(F(“Error opening datalog.txt file!”));
digitalWrite(13, LOW);

void loop () {

if (clockInterrupt) {

//read in our data
read3AxisAcceleration(); //loads up the dataString
DateTime now = RTC.now(); // Read the time and date from the RTC

if (cycle==1){
BMAdata1 = BMAdata;
Vcc1 = (readVcc());
Temp3231a = get3231Temp();
sprintf(TimeStampbuffer1, “%04d/%02d/%02d %02d:%02d:%02d,”, now.year(), now.month(), now.day(), now.hour(), now.minute(), now.second());

//Serial.print(TimeStampbuffer1); Serial.print(Vcc1); Serial.print(“,”);
//Serial.print(BMAdata1); Serial.print(“,”); Serial.println(Temp3231a);

if (cycle==2){
BMAdata2 = BMAdata;
Vcc2 = int(readVcc());
Temp3231b = get3231Temp();
sprintf(TimeStampbuffer2, “%04d/%02d/%02d %02d:%02d:%02d,”, now.year(), now.month(), now.day(), now.hour(), now.minute(), now.second());
//Serial.println(“Timestamp Y/M/D, HH:MM:SS, Vcc = , X = , Y = , Z = , BMATemp (C) , RTC temp (C)”);
//Serial.print(TimeStampbuffer2); Serial.print(Vcc2); Serial.print(“,”);
//Serial.print(BMAdata2); Serial.print(“,”); Serial.println(Temp3231b);

if (cycle==3){ //only write to mem card on this cycle
BMAdata3 = BMAdata;
Vcc3 = int(readVcc());
Temp3231c = get3231Temp();
sprintf(TimeStampbuffer3, “%04d/%02d/%02d %02d:%02d:%02d,”, now.year(), now.month(), now.day(), now.hour(), now.minute(), now.second());
//Serial.println(“Timestamp Y/M/D, HH:MM:SS, Vcc = , X = , Y = , Z = , BMATemp (C) , RTC temp (C)”);
//Serial.print(TimeStampbuffer3); Serial.print(Vcc3); Serial.print(“,”);
//Serial.print(BMAdata3); Serial.print(“,”); Serial.println(Temp3231c);

// the whole dataset looks like 0000/00/00 00:00:00,0000,0000,0000,0000,00000,00000
// if Vcc too low, dont write to the sd card
if (Vcc1 > 2850){
//Serial.println(F(“-write cycle performed-“)); delay (50);//for debugging only

File dataFile = SD.open(“datalog.txt”, FILE_WRITE);
if (dataFile) { // if the file is available, write to it:
//here we do the two writes at one time – hopefully saving power only writing every second cycle
dataFile.print(TimeStampbuffer1);dataFile.print(Vcc1); dataFile.print(“,”);
dataFile.print(BMAdata1); dataFile.print(“,”); dataFile.println(Temp3231a);

dataFile.print(TimeStampbuffer2);dataFile.print(Vcc2); dataFile.print(“,”);
dataFile.print(BMAdata2); dataFile.print(“,”); dataFile.println(Temp3231b);

dataFile.print(TimeStampbuffer3);dataFile.print(Vcc3); dataFile.print(“,”);
dataFile.print(BMAdata3); dataFile.print(“,”); dataFile.println(Temp3231c);

else { //if the file isn’t open, pop up an error:
Serial.println(F(“Error opening datalog.txt file”));
// setNextAlarmTime();
Alarmhour = now.hour(); Alarmminute = now.minute()+SampleInterval;
if (Alarmminute > 59) { //error catch – if alarmminute=60 the interrupt never triggers due to rollover!
Alarmminute =0; Alarmhour = Alarmhour+1; if (Alarmhour > 23) {Alarmhour =0;}
RTC.setAlarm1Simple(Alarmhour, Alarmminute);

//print lines commented out for deployment
//Serial.print(F(“Alarm Enabled at: “));
//Serial.print(now.hour(), DEC); Serial.print(‘:’); Serial.println(now.minute(), DEC);
//Serial.print(F(“Going to Sleep for “)); Serial.print(SampleInterval);Serial.println(F(” minutes.”));
//delay(100); //a delay long enought to boot out the serial coms

cycle ++;
if (cycle>3){


//Serial.println(F(“Alarm 1 has been Triggered!”));
void sleepNow() {
//digitalWrite(13, LOW);
cbi(ADCSRA,ADEN); // Switch ADC OFF
attachInterrupt(0,clockTrigger, LOW);
sbi(ADCSRA,ADEN); // Switch ADC converter ON
//digitalWrite(13, HIGH);

void clockTrigger() {
clockInterrupt = true; //do something quick, flip a flag, and handle in loop();

void clearClockTrigger()
Wire.beginTransmission(0x68); //Tell devices on the bus we are talking to the DS3231
Wire.write(0x0F); //Tell the device which address we want to read or write
Wire.endTransmission(); //Before you can write to and clear the alarm flag you have to read the flag first!
Wire.requestFrom(0x68,1); // Read one byte
dummyRegister=Wire.read(); // In this example we are not interest in actually using the bye
Wire.beginTransmission(0x68); //Tell devices on the bus we are talking to the DS3231
Wire.write(0x0F); //Tell the device which address we want to read or write
Wire.write(0b00000000); //Write the byte. The last 0 bit resets Alarm 1
clockInterrupt=false; //Finally clear the flag we use to indicate the trigger occurred

// could also use RTC.getTemperature() from the library here as in:
// RTC.convertTemperature(); //convert current temperature into registers
// Serial.print(RTC.getTemperature()); //read registers and display the temperature

float get3231Temp()
//temp registers (11h-12h) get updated automatically every 64s
Wire.requestFrom(DS3231_I2C_ADDRESS, 2);

if(Wire.available()) {
tMSB = Wire.read(); //2’s complement int portion
tLSB = Wire.read(); //fraction portion

temp3231 = ((((short)tMSB << 8 | (short)tLSB) >> 6) / 4.0); // Allows for readings below freezing – Thanks to Coding Badly
//temp3231 = (temp3231 * 1.8 + 32.0); // Convert Celcius to Fahrenheit
return temp3231;

else {
temp3231 = 255.0; //Use a value of 255 to error flag that we did not get temp data from the ds3231

return temp3231;
byte read3AxisAcceleration()
for(int i = 0; i < 7;i++)
dataArray[i] = Wire.read();

BMAtemp = dataArray[6];
x = dataArray[1] << 8;
x |= dataArray[0];
x >>= 6;
y = dataArray[3] << 8;
y |= dataArray[2];
y >>= 6;
z = dataArray[5] << 8;
z |= dataArray[4];
z >>= 6;

BMAdata = String(“”); //clear out the datastring
BMAdata += String(x);
BMAdata += “,”;
BMAdata += String(y);
BMAdata += “,”;
BMAdata += String(z);
BMAdata += “,”;
BMAtempfloat = (BMAtemp*0.5)+24.0;
// add digits of BMAtempfloat value to datastring
BMAdata += ((int)BMAtempfloat);
BMAdata += “.”;
int temp = (BMAtempfloat – (int)BMAtempfloat) * 100;
BMAdata += (abs(temp));
//this also works to convert float to string
//dtostrf(floatVariable2convert, minStringWidthIncDecimalPoint, numVarsAfterDecimal, charBuffer);
//for example: dtostrf(BMAtempfloat, 5, 2, dtostrfbuffer); dataString += dtostrfbuffer;
byte initializeBMA()
Wire.write(0x0F); //set g
Wire.write(0x10); //set bandwith

long readVcc() { //trick to read the Vin using internal 1.1 v as a refrence
long result;
// Read 1.1V reference against AVcc
ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
delay(3); // Wait for Vref to settle
ADCSRA |= _BV(ADSC); // Convert
while (bit_is_set(ADCSRA,ADSC));
result = ADCL;
result |= ADCH<<8;
result = 1126400L / result; // Back-calculate AVcc in mV
return result;

int freeRam () {
extern int __heap_start, *__brkval;
int v;
return (int) &v – (__brkval == 0 ? (int) &__heap_start : (int) __brkval);

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