What a groaner.. who needs another datalogger? Well I do, so stuff it. I was inspired to check out these iButtonLink devices that allow you to daisy-chain connect a number of devices in a single circuit of sorts with RJ45 patch cables. I had seen these a couple years ago in some top-notch datacenters that terminated to a concentrator (4 strings) that were then pushed up to some IBM services app server.

A while back I published a Microsoft PIC microcontroller version of this … I decided to give it another whirl with the “easy button” … Arduino. Of course there were a couple libraries that I just had to collectively stuff into the same sketch and easy-peasy it was done in an hour or so.

This time I have my data stored to an SD card, which … I hastily put together.

If I was actually going to finish this I would add three things to this to finish it up.

  1. Use an RTC, figure an interface to enter the correct time. (maybe add an ethernet shield and get NTP?) … or just manual enter.
  2. I’d grab the interval time off the RTC and just have the loop do a non-blocking wait, then poll the RTC time or interrupt (whatever you favorite way to do this is..) that way I was collecting trend information on the “:00″s.
  3. I would add a method of checking for an SD card to be interested and allow it to start logging from card insert. I would also add time/date stamp to the file and finally, still SD card related I would check file size and stop logging when I got close to full.

So that is that. I’ve been creating a lot of fun lately but nothing mind-bending.. just going through every module I’ve ever bought doing the demo code … or going the other way around.. working on every Arduino demo/example in a class .. I’ve also built an FE boat, moved my workshop inside (update video coming kind of soon) and been working on PopBot 0.5 ..

The code:

 * Chas Ihler
 * @chasxmd
 * https://iradan.com
 * License: Public Domain - it's mostly copy and paste and preferences anyways.
 * iButtonLink, grabs all sensors and logs them to card if present.
 * Recommendations: 
 * Add an RTC and a method of updating time. 
 * I'd also grab actual seconds off the RTC for logging and use a non-blocking wait for the polling/logging. 
 * Libraries:
 * https://github.com/matmunk/DS18B20
 * IDE built in SD card/SPI library
 * Sensor: 
 * https://www.ibuttonlink.com/products/t-sense-temperature-sensor
 * which has this device within.. 
 * https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf
 * Hookup:
 * You'll need a pullup resistor from 5V to pin 2
 * ibutton hookup:
 * 1 - GND
 * 2 - 5VDC
 * 3 - NC
 * 4 - Arduino Pin 2 (w/ Pullup)
 * 5 - GND
 * 6 - NC
 * 7 - NC
 * 8 - NC
 *  SD card attached to SPI bus as follows:
 * MOSI - pin 11
 * MISO - pin 12
 * CLK - pin 13
 * CS - pin 4 

#include <DS18B20.h>
#include <SPI.h>
#include <SD.h>

DS18B20 ds(2);    //pin 2

const int chipSelect = 4;

void setup() {

  Serial.println(" ");
  Serial.println("DS18B20 / iButtonLink Demo");
  Serial.print("Devices: ");
  Serial.println(" ");
   Serial.print("Initializing SD card...");

  // see if the card is present and can be initialized:
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    // don't do anything more:
    while (1);
  Serial.println("card initialized.");

void loop() {
  int i_address;
  while (ds.selectNext()) {
    String str_dataString = "";
    switch (ds.getFamilyCode()) {
      case MODEL_DS18S20:
        Serial.println("Model: DS18S20/DS1820");
      case MODEL_DS1822:
        Serial.println("Model: DS1822");
      case MODEL_DS18B20:
        Serial.println("Model: DS18B20");
        Serial.println("Unrecognized Device");

    uint8_t address[8];
    for (uint8_t i = 0; i < 8; i++) {
      Serial.print(" ");
      str_dataString += String(address[i]);
    Serial.print("Resolution: ");

    Serial.print("Power Mode: ");
    if (ds.getPowerMode()) {
    } else {
    Serial.print("Temperature: ");
    Serial.print(" C / ");
    Serial.println(" F");
    str_dataString += ",";
    str_dataString += String(ds.getTempC()); 
    File dataFile = SD.open("datalog.txt", FILE_WRITE);
    if (dataFile) {
    }  else {
        Serial.println("error opening datalog.txt");
    Serial.println("        *****       ");


Happy Making!

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