DS18B20 Temperature Sensor on Long Runs

Running a DS18B20 on 100 meters of cable introduces challenges that don't exist on a breadboard. Here's what matters.

With parasitic power mode, long cable runs cause voltage droop on the bus during strong pull-up mode (the high-current pull-up needed for temperature conversion). Switch to external (three-wire) power mode for runs over 10m — pin 2 connected to VDD, not to GND. Twisted pair cable between the MCU and sensor helps cancel common-mode noise.

For very long runs, a 4.7kΩ pull-up at the sensor end (not the MCU end) keeps the line high without relying on the MCU to drive it against cable capacitance. Add a 100nF cap from VDD to GND at the sensor. With these precautions I've had reliable DS18B20 operation at 80m without shielded cable. For 100m+ or electrically noisy environments, consider switching to a 4-20mA current loop temperature transmitter instead.