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NodeMCU NodeMCU is formed by an ESP12E

Si7021 Sensor  for measuring humidity and temperature The  Si7021  Sensor  integrates   humidity   and   temperature   sensor   elements,   an   analog-to-digital converter, signal processing, calibration data, and an I2C Interface. The Si7021 offers an accurate, low-power, factory-calibrated digital solution ideal for measuring humidity and temperature Features Precision Relative Humidity Sensor ± 3% RH (max), 0–80% RH High Accuracy Temperature Sensor ±0.4 °C (max), –10 to 85 °C 0 to 100% RH operating range Up to –40 to +125 °C operating range Wide operating voltage – (1.9 to 3.6 V) Low Power Consumption – 150 μA active current How to wire https://learn.sparkfun.com/tutorials/si7021-humidity-and-temperature-sensor-hookup-guide/all Library https://github.com/adafruit/Adafruit_Si7021/blob/master/examples/si7021/si7021.ino#L36

I built few thermometers powered by battery to check temperature's rooms in my house. For my tests I used : Webmos d1 mini 18650 battery  Sensor Si7021