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I try to use a new DS18B20+ temperature sensor (sealed water proof version).

It doesn't work. My own code doesn't work, examples from DallasTemperature Library don't work, example from OneWire library doesn't work.

For example function sensors.getDeviceCount(); (DallasTemperature library) returns '0'. Function tempSensor.getTempCByIndex(0); returns 65409 (int variable). !ds.search(addr) (OneWire library) also always return '0'. Then I am sure, Arduino code is alright.

I am sure DS18B20 is connected correctly:

  • white wire (onewire data) - onewire Arduino pin (tested with pin 2 and pin 13)
  • red wire (+V) - 5V Arduino pin
  • black wire (GND) - GND Arduinp pin
  • between 5V and DATA there is a 4k7 resistor

I have measured resistances between the temperature sensor's wires:

  • '+V' to 'data': 4,7 kOhm
  • 'GND' to 'data': ~3 Ohm

I think between the GND and DATA sensor wires resistance should be much higher - am I right? Below you can see a block diagram copied from the sensor datasheet (https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf): ds18b20 block diagram

Maybe black and white wires are +V and GND (which one is +V?), red is data? Or it's broken? Or something else?

I have bought it here - https://botland.com.pl/pl/czujniki-temperatury/10936-sonda-wodoodporna-z-czujnikiem-temperatury-ds18b20-5m-brazowy-silikon.html?search_query=sonda+temperatury&results=43 (language: polish). it is written:

  • VCC - red
  • GND - black or green
  • data 1-wire - white or yellow
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    between 5V and GND there is a 4k7 resistor the diagram tells you to pullup the data line (DQ) to V_PU (5V), not between 5V and ground. That is just a power dissipator. – Maximilian Gerhardt Feb 17 at 19:16
  • Yes, sorry, it was a typo. 4k7 is between the data and +V. – kot Feb 17 at 19:21
  • Can you verify the meaning of the wire colors according to the package information of the datasheet? All the "DS18B20+" I see on e.g. digikey don't have color-coded wires on them. Do you have a link to where you bought them? – Maximilian Gerhardt Feb 17 at 20:23
  • First post edited (added a link where I bought it) – kot Feb 17 at 20:26
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    If you measure 3 Ohms then there is a short between the wires. The sensor is bad. – Rudy Feb 17 at 21:24

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