{"id":52225,"date":"2026-11-01T10:50:41","date_gmt":"2026-11-01T10:50:41","guid":{"rendered":"http:\/\/siratek.net\/index.php\/tutorials\/ds18b20-waterproof-temperature\/"},"modified":"2026-11-01T10:50:41","modified_gmt":"2026-11-01T10:50:41","slug":"ds18b20-waterproof-temperature","status":"publish","type":"siratek_tutorial","link":"https:\/\/siratek.net\/index.php\/tutorials\/ds18b20-waterproof-temperature\/","title":{"rendered":"Waterproof Temperature with DS18B20"},"content":{"rendered":"

<\/p>\n

What it does<\/h2>\n

A DS18B20 in a stainless steel probe on the end of a cable. It reads from about -55 to +125 degrees Celsius to a tenth of a degree, and the sealed tip means it can go into soil, a tank, a fermenter or a fridge.<\/p>\n

It is a better sensor than the DHT11 in every way that matters for temperature: more accurate, much wider range, and it does not have to be kept dry. It also introduces something new, because it speaks 1-Wire<\/strong>, a protocol where data and the clock share a single line, and many devices share that one line.<\/p>\n

Before you begin<\/h2>\n

Required parts and tools<\/h3>\n
    \n
  • An Arduino Uno or compatible board.<\/li>\n
  • One waterproof DS18B20 probe. This is Siratek product 49704.<\/li>\n
  • One 4.7 kilohm resistor. The sensor will not work without it, and one is not supplied.<\/strong><\/li>\n
  • A breadboard and three jumper wires.<\/li>\n<\/ul>\n

    Three bare wires<\/h3>\n

    The Siratek part is a probe with a one-metre cable ending in three tinned wires, no connector and no breakout board<\/strong>:<\/p>\n\n\n\n\n\n\n\n
    Wire<\/th>\nFunction<\/th>\n<\/tr>\n<\/thead>\n
    Red<\/td>\nVDD<\/code>, 3.0 to 5.5 V<\/td>\n<\/tr>\n
    Yellow<\/td>\nDQ<\/code>, the data line<\/td>\n<\/tr>\n
    Black<\/td>\nGND<\/code><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    Colours are near-universal on these probes but not guaranteed. If yours differ, the data wire is the one that is neither red nor black.<\/p>\n

    Bare wire ends do not sit reliably in a breadboard. Tin them, fit a short length of solid-core wire, or use a small screw terminal. A probe that works when you hold the wires and fails when you let go is a connection problem, not a sensor problem.<\/p>\n

    The pull-up resistor, which is the whole trick<\/h3>\n

    1-Wire works by letting every device pull a single shared line down<\/strong>, and nothing ever drives it up. The line is held high by one resistor, and any device can win by pulling it low.<\/p>\n

    That resistor is not in the probe. You have to fit it: 4.7 kilohms between the yellow data wire and the red power wire.<\/strong><\/p>\n

    Leave it out and the data line floats. The sensor is found inconsistently or not at all, and the library returns -127.00<\/code>, which is its code for \u201cno reply\u201d. Almost every \u201cmy DS18B20 reads -127\u201d is this.<\/p>\n

    A second value worth knowing: 85.00<\/strong> means the sensor powered up and was read before it finished its first conversion. That one is usually a timing or power problem rather than wiring.<\/p>\n

    Why one line can hold many sensors<\/h3>\n

    Every DS18B20 leaves the factory with a unique 64-bit address burnt into it. Because each one answers only to its own address, you can connect a dozen probes to the same pin with the same one resistor, and read them individually.<\/p>\n

    That is genuinely useful: a tank with probes at three depths costs you one Arduino pin. The example below starts with one, then shows how to find and read several.<\/p>\n

    Pin reference<\/h2>\n\n\n\n\n\n\n\n
    Wire<\/th>\nConnect to<\/th>\nPurpose<\/th>\nNotes<\/th>\n<\/tr>\n<\/thead>\n
    Red<\/td>\nUno 5V<\/code><\/td>\nPower<\/td>\n3.3 V works too<\/td>\n<\/tr>\n
    Yellow<\/td>\nUno D2<\/code>, and<\/strong> through 4.7 k to 5V<\/code><\/td>\nData<\/td>\nThe resistor is required<\/td>\n<\/tr>\n
    Black<\/td>\nUno GND<\/code><\/td>\nGround<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \"A
    The 4.7 kilohm pull-up is not supplied with the probe and nothing works without it.<\/figcaption><\/figure>\n

    Wiring steps<\/h2>\n
      \n
    1. Unplug the USB cable.<\/li>\n
    2. Put the three wire ends into three separate breadboard rows.<\/li>\n
    3. Red to 5V<\/code>.<\/li>\n
    4. Black to GND<\/code>.<\/li>\n
    5. Yellow to D2<\/code>.<\/li>\n
    6. Fit the 4.7 k resistor between the yellow wire\u2019s row and the 5V<\/code> rail.<\/li>\n
    7. Check that the resistor really bridges data and power. This is the step people skip.<\/li>\n
    8. Plug the USB cable back in.<\/li>\n<\/ol>\n

      Software and libraries<\/h2>\n

      Install two libraries through Library Manager:<\/p>\n

        \n
      • OneWire<\/strong>, which handles the protocol.<\/li>\n
      • DallasTemperature<\/strong>, which turns it into readable calls.<\/li>\n<\/ul>\n

        The second needs the first. Install OneWire too if Library Manager does not bring it along.<\/p>\n

        Minimal working example<\/h2>\n
        \/\/ Siratek: reading one DS18B20 probe.\n\n#include <OneWire.h>\n#include <DallasTemperature.h>\n\nconst int oneWirePin = 2;\n\nOneWire oneWire(oneWirePin);\nDallasTemperature sensors(&oneWire);\n\nvoid setup() {\n  Serial.begin(9600);\n  sensors.begin();\n\n  Serial.print(\"Siratek: found \");\n  Serial.print(sensors.getDeviceCount());\n  Serial.println(\" sensor(s).\");\n}\n\nvoid loop() {\n  sensors.requestTemperatures();\n  float c = sensors.getTempCByIndex(0);\n\n  if (c == DEVICE_DISCONNECTED_C) {\n    Serial.println(\"no reply. Check the 4.7k pull-up.\");\n  } else {\n    Serial.print(\"temperature = \");\n    Serial.print(c, 1);\n    Serial.println(\" C\");\n  }\n\n  delay(1000);\n}<\/code><\/pre>\n
        The device count printed in setup()<\/code> is the first thing to look at. Zero means the wiring is wrong<\/strong>, almost always the resistor, and no amount of reading further output will help.<\/p>\n
        Checking against DEVICE_DISCONNECTED_C<\/code> rather than printing whatever arrives is worth the two lines. It turns a mysterious -127.00<\/code> into a sentence that names the cause.<\/p>\n
        Several probes on one pin<\/h3>\n
        \/\/ Siratek: reading every DS18B20 on the line.\n\n#include <OneWire.h>\n#include <DallasTemperature.h>\n\nOneWire oneWire(2);\nDallasTemperature sensors(&oneWire);\n\nint count = 0;\n\nvoid setup() {\n  Serial.begin(9600);\n  sensors.begin();\n  count = sensors.getDeviceCount();\n\n  Serial.print(\"Siratek: \");\n  Serial.print(count);\n  Serial.println(\" probe(s) on the line.\");\n}\n\nvoid loop() {\n  sensors.requestTemperatures();\n\n  for (int i = 0; i < count; i++) {\n    Serial.print(\"probe \");\n    Serial.print(i);\n    Serial.print(\" = \");\n    Serial.print(sensors.getTempCByIndex(i), 1);\n    Serial.println(\" C\");\n  }\n\n  Serial.println();\n  delay(2000);\n}<\/code><\/pre>\n
        One warning about getTempCByIndex()<\/code>: the index is the order the library discovered the devices in, which depends on their addresses, not on where they are in your tank. Add a probe and the numbering can change.<\/p>\n
        For anything permanent, read each sensor\u2019s address once with getAddress()<\/code>, write those addresses into your sketch, and read by address. Then \u201cprobe 0\u201d means the probe you meant.<\/p>\n
        Why reading takes time<\/h3>\n
        requestTemperatures()<\/code> waits while the sensor converts. At the default 12-bit resolution that is up to 750 milliseconds<\/strong>, during which your sketch does nothing else.<\/p>\n
        Three quarters of a second is a long time in a loop that is also watching a button. The fixes, in order of effort: lower the resolution with setResolution(9)<\/code>, which takes about 94 ms and gives half a degree instead of a sixteenth; or call setWaitForConversion(false)<\/code> and collect the reading on a later pass, using the pattern from Timing Without delay()<\/em>.<\/p>\n
        For a thermometer that updates once a second, leave it alone.<\/p>\n
        Expected result<\/h2>\n
        A device count of 1 in setup()<\/code>, then a temperature once a second to one decimal place.<\/p>\n
        Hold the metal tip between your fingers and the reading should climb within a few seconds. It will not jump instantly: the steel sheath has to warm up first, and that thermal lag is real and worth knowing about if you are measuring something that changes quickly.<\/p>\n
        Troubleshooting<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
        Symptom<\/th>\nLikely cause<\/th>\nCheck or fix<\/th>\n<\/tr>\n<\/thead>\n
        Reads -127.00<\/td>\nNo pull-up resistor<\/td>\n4.7 k between the data wire and 5V<\/code><\/td>\n<\/tr>\n
        Found 0 sensors<\/td>\nSame, or data on the wrong pin<\/td>\nCheck the resistor, then the pin number<\/td>\n<\/tr>\n
        Reads 85.00<\/td>\nRead before the first conversion finished<\/td>\nCheck power; let requestTemperatures()<\/code> complete<\/td>\n<\/tr>\n
        Works when held, fails when let go<\/td>\nBare wires not seated<\/td>\nTin the ends or use a screw terminal<\/td>\n<\/tr>\n
        Readings jump between two values<\/td>\nLoose connection, or a long unshielded cable<\/td>\nReseat; try 2.2 k for a long run<\/td>\n<\/tr>\n
        One of several probes disappears<\/td>\nIndex order changed<\/td>\nRead by address, not by index<\/td>\n<\/tr>\n
        Sketch feels sluggish<\/td>\n750 ms conversion time<\/td>\nLower the resolution, or do not block<\/td>\n<\/tr>\n
        Compile error about OneWire<\/td>\nLibrary missing<\/td>\nInstall OneWire as well as DallasTemperature<\/td>\n<\/tr>\n
        Reading is right but slow to change<\/td>\nThermal mass of the steel tip<\/td>\nExpected; allow it to settle<\/td>\n<\/tr>\n
        Reads correctly in air, wrongly in water<\/td>\nCable entry not sealed<\/td>\nOnly the tip is waterproof; keep the joint dry<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
        Next steps<\/h2>\n
          \n
        • Easier first:<\/strong> Read Temperature and Humidity with DHT11<\/em>, which needs no extra resistor.<\/li>\n
        • Related:<\/strong> I2C, Two Wires and Many Devices<\/em>, to compare how the two shared buses address devices.<\/li>\n
        • Next project:<\/strong> a standalone data logger, writing temperature and a timestamp to an SD card.<\/li>\n<\/ul>\n
          Sources and attribution<\/h2>\n
          All text, wiring guidance and code in this tutorial are original Siratek work.<\/p>\n
            \n
          • Maxim DS18B20 datasheet for the temperature range, the 64-bit address, the conversion times at each resolution and the recommended pull-up value.<\/li>\n
          • DallasTemperature and OneWire library documentation for the calls used.<\/li>\n<\/ul>\n
            The probe described here has three bare wires and no breakout board, read from the Siratek product photograph for item 49704, which is why the pull-up resistor is treated as a required part rather than an optional one. Wire colours are near-universal on these probes but the reader is told what to do if theirs differ. No third-party tutorial text, diagrams, photographs or code has been reproduced here.<\/p>\n
            <\/p>\n<\/body>","protected":false},"excerpt":{"rendered":"
            A DS18B20 in a stainless steel probe on the end of a cable. It reads from about -55 to +125 degrees Celsius to a tenth of a degree, and the sealed tip means it can go into soil, a tank,…<\/p>\n","protected":false},"featured_media":0,"template":"","siratek_tutorial_level":[],"class_list":["post-52225","siratek_tutorial","type-siratek_tutorial","status-publish","hentry"],"yoast_head":"\nWaterproof Temperature with DS18B20 - siratek<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"http:\/\/siratek.net\/index.php\/tutorials\/ds18b20-waterproof-temperature\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Waterproof Temperature with DS18B20 - siratek\" \/>\n<meta property=\"og:description\" content=\"A DS18B20 in a stainless steel probe on the end of a cable. 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