DS18B20 with LOLIN S2 Mini — wiring and code

DS18B20 probes are the standard for tank and pipe temperatures. On the S2 Mini use GPIO16 — the same position as D4 on a D1 mini — with a 4.7 kΩ pull-up to 3V3.

The sketch counts the probes at start-up and prints the first one’s temperature every second.

Wiring

Board quirks

• GPIO16 is in the D1 mini’s D4 position, the usual DS18B20 pin on D1 mini shields. On the S2 it has no boot role (unlike D4/GPIO2 on the ESP8266).
• GPIO18 next to it has a 10 kΩ on-board pull-up. That also works for a short single probe, but 4.7 kΩ on GPIO16 is more reliable for long cables and several probes.
• OneWire 2.3.8 supports the S2’s GPIO registers, so the usual DallasTemperature code runs unchanged.

Code

// DS18B20 probe on a LOLIN S2 Mini.
// VDD → 3V3, DQ → GPIO16 with a 4.7 kΩ pull-up to 3V3, GND → GND.
#include <OneWire.h>
#include <DallasTemperature.h>

constexpr uint8_t ONE_WIRE_PIN = 16;
OneWire oneWire(ONE_WIRE_PIN);
DallasTemperature sensors(&oneWire);

void setup() {
  Serial.begin(115200);
  uint32_t t0 = millis();
  while (!Serial && millis() - t0 < 3000) {}
  sensors.begin();
  Serial.printf("DS18B20 on GPIO16 - %u sensor(s) found\n", sensors.getDeviceCount());
}

void loop() {
  sensors.requestTemperatures();
  float t = sensors.getTempCByIndex(0);
  if (t == DEVICE_DISCONNECTED_C) Serial.println("No sensor answered - check the 4.7 kOhm pull-up");
  else Serial.printf("Temperature: %.2f C\n", t);
  delay(1000);
}

// DS18B20 probe on a LOLIN S2 Mini.
// VDD → 3V3, DQ → GPIO16 with a 4.7 kΩ pull-up to 3V3, GND → GND.
#include <OneWire.h>
#include <DallasTemperature.h>

constexpr uint8_t ONE_WIRE_PIN = 16;
OneWire oneWire(ONE_WIRE_PIN);
DallasTemperature sensors(&oneWire);

void setup() {
  Serial.begin(115200);
  uint32_t t0 = millis();
  while (!Serial && millis() - t0 < 3000) {}
  sensors.begin();
  Serial.printf("DS18B20 on GPIO16 - %u sensor(s) found\n", sensors.getDeviceCount());
}

void loop() {
  sensors.requestTemperatures();
  float t = sensors.getTempCByIndex(0);
  if (t == DEVICE_DISCONNECTED_C) Serial.println("No sensor answered - check the 4.7 kOhm pull-up");
  else Serial.printf("Temperature: %.2f C\n", t);
  delay(1000);
}

Library: DallasTemperature (Miles Burton (also install OneWire by Jim Studt / Paul Stoffregen)) — compiled with OneWire 2.3.8.

Expected serial output

DS18B20 on GPIO16 - 1 sensor(s) found
Temperature: 25.81 C
Temperature: 25.87 C

DS18B20 on GPIO16 - 1 sensor(s) found
Temperature: 25.81 C
Temperature: 25.87 C

Common errors