Friday, November 18, 2011

TomWare Arduino-Ethernet Datalogger

Arduino-Ethernet Datalogger
last updated on nov 18 2011

For a customer project I needed to build a datalogger that had to be periodically and asynchronously polled via ethernet. Main task of the datalogger was counting raising pulses from an external sensor outputting a TTL 0-5v  signal.

Customer requirements were to have it simple, reliable, and tolerant of possible ethernet network disconnections.

I decided to work using the new Arduino Ethernet, which integrates the wiznet ethernet shield, and also has the sdcard slot.
I made this with Arduino022 software version.

I needed to perform accurate timestamping in the logs, so I decided to use NTP protocol to periodically sync a local clock built via the DS1307RTC time library.
Given the nature of the pulses I had to count, I decided to simply connect the counter line using the interrupt feature, and so decoupling the pulse detection from all the other code.

After initializing network, sdcard, synchronizing time with NTP server, and setting up the interrupt pulsereading line, the main loop just cycles waiting for browser to connect, then checking if it is time to log on the sdcard, and checking if it is time to resync clock with NTP to avoid excessive drift.

To test it, I built a simple random pulse generator and run it on another arduino 2009, feeding its digital output to the Arduino ethernet pulsecounter in.

I used just the external timekeeping library

Here is the code. Some portions are freely taken from arduino libraries samples. Also I got some inspiration from this page by Ms. Limor Fried (aka LadyAda) describing her SDcard Datalogger and Ethernet server. My SD code is different (and a bit simpler) because I use the standard SD card library.

Web Server, Pulse Logger, NTP time client, for Carcano spa
This code is GPL. see for details

be careful in increasing string space. this software uses almost all the arduino ATMEGA328 memory (2Kb)

SDcard Datalogger v0.8

TCPIP Webserver with 
NTP client
Asynchronous Interrupt (IRQ0) pulse counter on Digital pin2
DataLogger on Micro SDcard file

* Ethernet shield attached to pins 10, 11, 12, 13
* Analog inputs attached to pins A0 through A5 (optional)
* Digital input with raising front pulse counter on digital PIN2

NTP protocol is used to sync from a time server 
in arduino 022 download
   and put its contents in 

SDcard is accessed via SPI protocol standard, which is also used to program ethernet Wiznet controller.
In order to interact with SD, we need to set pin10 as output otherwise SD library will not work



byte mac[] = { 0xDA, 0xAD, 0xBE, 0xEE, 0xFE, 0xED };
byte ip[] = { 10, 2, 3, 51 };
byte mask[] = { 255, 255, 0, 0 };
byte gateway[] = { 10, 2, 0, 1 };
byte timeServer[] = { 10, 2, 3, 60 };
                                          // seconds to add to UTCtime to consider correct timezone
// const unsigned long UTCcorrection = 7200; // CET = UTC + 1 (+2 in summer):  (HOW to properly calculate DST?)
const unsigned long UTCcorrection = 0;    // keep UTC
const int NTP_PACKET_SIZE= 48;            // NTP time stamp is in the first 48 bytes of the message
byte packetBuffer[NTP_PACKET_SIZE];       // buffer to hold incoming and outgoing packets
unsigned int localPort = 8989;            // local port to listen for UDP packets
Server server(80);                        // local listener port for http services

// variable for pulsecounter, to be altered from inside interrupt routine (requires volatile)
volatile unsigned long pulses = 0;
int pulsePin = 2;  // use pin2 for async pulse counter IRQ0 is connected to PIN2, (IRQ1 is connected to pin 3)

const unsigned long seventyYears = 2208988800UL;     
unsigned long epoch = seventyYears;

const int EthChipSelect = 10;
const int SDChipSelect = 4;
time_t logInterval = 10UL;          // append to file every loginterval seconds
time_t lastLogTime = 0UL;         
time_t syncInterval = 60UL;         // ntp sync every syncinterval seconds
time_t lastSyncTime = 0UL;        

unsigned long logLinesWritten = 0;
const int maxLogLines = 7;
boolean fileFull = false;
char* logFileName = "log.txt";
unsigned long logFileSize = 0;  //logfilesize added from last powerup

unsigned long sendNTPpacket(byte *address) {
  memset(packetBuffer, 0, NTP_PACKET_SIZE); // set all bytes in the buffer to 0
  // Initialize values needed to form NTP request
  packetBuffer[0] = 0b11100011;   // LI, Version, Mode
  packetBuffer[1] = 0;     // Stratum, or type of clock
  packetBuffer[2] = 6;     // Polling Interval
  packetBuffer[3] = 0xEC;  // Peer Clock Precision
  // 8 bytes of zero for Root Delay & Root Dispersion
  packetBuffer[12]  = 49;
  packetBuffer[13]  = 0x4E;
  packetBuffer[14]  = 49;
  packetBuffer[15]  = 52;
  // Now send packet requesting a timestamp to server udp port NTP 123
  Udp.sendPacket( packetBuffer,NTP_PACKET_SIZE, address, 123);

void ntpTimeSync() {
  sendNTPpacket(timeServer); // send an NTP packet to a time server & wait if a reply is available
  if ( Udp.available() ) {  
    Udp.readPacket(packetBuffer,NTP_PACKET_SIZE);  // read the packet into the buffer
    // the timestamp starts at byte 40 of the received packet and is four bytes,
    // or two words, long. First, esxtract the two words:
    unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
    unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);  
    // combine the four bytes (two words) into a longint: NTP time (seconds since Jan 1 1900)
    unsigned long secsSince1900 = highWord << 16 | lowWord;  
    // NTP gives secs from 1 1 1900. Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
    // subtract seventy years:
    epoch = secsSince1900 - seventyYears;  
  } else {
  time_t t = epoch + UTCcorrection;
  setTime(t);    // sets arduino internal clock

String getTimeString() {
  // gives back hh:mm:ss
  time_t t = now();
  String s = "";
  if (hour(t) <10) s = s + "0";
  s = s + hour(t) + ":";
  if (minute(t) <10) s = s + "0";
  s = s + minute(t) + ":";
  if (second(t) <10) s = s + "0";
  s = s + second(t);

String getDateString() {
  // gives back dd/mm/yyyy
  time_t t = now();
  String s = "";
  if (day(t) <10) s = s + "0";
  s = s + day(t) + "/";
  if (month(t) <10) s = s + "0";
  s = s + month(t) + "/";
  s = s + year(t);

void tic() {  // IRR Interrupt response routine, bump counter when signal raising front seen

void setup()
  // setup interrupt logic
  pinMode(pulsePin, INPUT);        // non strettamente necessaria, in quanto IRQ0 e' sempre agganciata a pin2
  attachInterrupt(0, tic, RISING); // LOW-CHANGE-RISING-FALLING tic is the function pointer to the RRI
  pinMode(EthChipSelect, OUTPUT);
  if (!SD.begin(SDChipSelect)) {
    while(1); // fatal: wait forever

void webServer() {
// sends log content if something is specified
  String creq;
  Client client = server.available();
  if (client) {
    while (client.connected()) {
      if (client.available()) {
        char c =;
        if (c != '\n' && c != '\r') {
          creq += c;
      if (creq[5] != 'x' && creq[5] != 'X') {      // or requests log, else std page
        client.println("HTTP/1.1 200 OK");
        client.println("Content-Type: text/html");
        client.print("TomWare PulseLogger 0.8");

http://ip/X ->log"); client.println("

"); client.print("T:"); client.print(getTimeString()); client.println("

"); client.print("D:"); client.print(getDateString()); client.println("

"); client.print("p2 pulses:"); client.print(pulses); client.print("

"); client.print("log:"); client.print(logFileName); client.println("

"); client.print("lines:"); client.print(logLinesWritten); client.println("

"); client.print("logsize:"); client.print(logFileSize); client.println("

"); client.print("ram:"); client.print(FreeRam()); client.println("

"); } else { // LOG REQUESTED File dataFile =, FILE_READ); if (! dataFile) { client.println("HTTP/1.1 404 Not Found"); client.println("Content-Type: text/html"); client.println(); client.println("File Not Found!"); } Serial.println("W"); client.println("HTTP/1.1 200 OK"); client.println("Content-Type: text/plain"); client.println(); char k; while ((k = > 0) { client.print((char)k); } dataFile.close(); if (fileFull) { // start a new file if file full, deleting contents just sent Serial.print("D"); SD.remove(logFileName); Serial.println("."); fileFull = false; } } delay(1); // give the web browser time to receive the data client.stop(); } } } void logToFile() { // always log to logFileName file File logFile =, FILE_WRITE); if (logFile) { String s = ""; time_t t = now(); s = String(t) + "," + String(pulses); for (int analogChannel = 0; analogChannel < 6; analogChannel++) { s += ","; s += String(analogRead(analogChannel)); } logFile.println(s); logFileSize = logFile.size(); logFile.close(); Serial.println(s); logLinesWritten++; } else { Serial.println("SDe!"); while(1); // fatal: wait forever } } void loop() { webServer(); time_t t = now(); if ((t - lastLogTime) >= logInterval) { lastLogTime = t; Serial.print("F:"); Serial.println(FreeRam()); Serial.print("L:"); Serial.println(logLinesWritten); logToFile(); if ((logLinesWritten % maxLogLines) == 0) { Serial.println("FF"); fileFull = true; } } if ((t - lastSyncTime) > syncInterval) { lastSyncTime = t; Serial.println("N"); ntpTimeSync(); } }

@mgua .


Unknown said...

This is Awesome I am working on a project that is close to this for school.

This is great....Thanks!!!

Krišus said...

Thank You for the nice code!
On what version of Arduino IDE is this built?
I am having problems compiling this on Arduino 1.0.1.

Thank You in advance!

Krišus said...

What version of Arduino IDE is used to compile this?
I am having problems on 1.0.1. Is that compatible?

Marco Guardigli said...

As mentioned in the blog entry, I worked with version 022 of arduino ide.

Changes should not be very big in order to adapt it to current version.


Anonymous said...

Thanks for this awesome piece of code. In your code you have a comment (HOW to properly calculate DST?). I found a perfect library which does that very easy (see You just have to define when your DST starts and when it ends like this for CES / CEST:

// Timezone Definition --------------------------------------------
//Central European Time (Switzerland, Germany, France) --> see Timezone Library for further informations (
//Central European Summer Time - begin of DST {abbrev, week, dow, month, hour, offset} -> last Sunday in March, at 2 o'clock adding 2 hours to UTC
TimeChangeRule CEST = {"CEST", Last, Sun, Mar, 2, 120};
//Central European Standard Time - end of DST {abbrev, week, dow, month, hour, offset} -> last Sunday in October, at 3 o'clock adding 1 hours to UTC
TimeChangeRule CET = {"CET ", Last, Sun, Oct, 3, 60};
Timezone CE(CEST, CET); //set Timezone CE using definitions CEST and CET
TimeChangeRule *tcr; //pointer to the time change rule, use to get the TZ abbrev

CE.locIsDST(local) // boolean: true if DST is active at the moment, false if not

local = CE.toLocal((secsSince1900 - 2208988800UL), &tcr);

Marco Guardigli said...

thank you!
Jack Christiansen code was not available when I wrote mine.
I remember having some memory full issues with that code, so be careful.


Unknown said...

hello Marco very nice project , I compiled the project with the current version of Arduino and I can not compile it, and my idea 'to use a mega with ethernet shield, you have any suggestions?

Unknown said...

Hi Marco. I'm trying to compile your code. And it's giving me next errors:

sketch_feb27a.cpp: In function 'String getTimeString()':
sketch_feb27a:130: error: 'ss' was not declared in this scope
sketch_feb27a:131: error: 'ss' was not declared in this scope
sketch_feb27a.cpp: In function 'String getDateString()':
sketch_feb27a:144: error: 'ss' was not declared in this scope
sketch_feb27a:145: error: 'ss' was not declared in this scope
sketch_feb27a.cpp: In function 'void logToFile()':
sketch_feb27a:273: error: 'logFilelogFileSize' was not declared in this scope
sketch_feb27a.cpp: At global scope:
sketch_feb27a:307: error: expected unqualified-id before '<' token