What is a SHT85 sensor ?

The SHT85 is Sensirion's reference sensor for very high-precision digital humidity and temperature measurement.

It is an improved and encapsulated version of the SHT3x, featuring:

• a plug-in connector for quick replacement,
• a hydrophobic PTFE coating,
• and total protection against condensation and corrosive agents.

It is designed for demanding environments where reliability and traceability are essential.

Operating principle

The SHT85 integrates a capacitive humidity sensor and a diode temperature sensor, combined with a 14-bit ΔΣ converter.

The calculation of temperature and humidity is digital and calibrated via EEPROM.

Standard Sensirion formulas:

T (°C) = -45 + (175 × SO_T) / 65535

RH (%) = 100 × SO_RH / 65535

💡 SO_T and SO_RH = raw values read on 16 bits.

Example of digital conversion (pseudo-code SPI-like)

// Example of I²C standard compatible UART via converter
sendCommand(0x2400); // Lecture T + RH
wait(20);
readBytes(buffer, 6);

uint16_t rawT = (buffer[0] << 8) | buffer[1];
uint16_t rawRH = (buffer[3] << 8) | buffer[4];

float T = -45 + 175 * ((float)rawT / 65535.0);
float RH = 100 * ((float)rawRH / 65535.0);

✅ Typical example:

T = 23,6 °C | RH = 47,4 %

Principle diagram

+3.3V
 │
[SHT85]
 │ SDA / TX ─────┐
 │ SCL / RX ─────┤── MCU (I²C or UART depending on configuration)
 │ GND

💡 The UART mode requires a compatible TTL serial converter (e.g., FT232, CP2102).

Application areas

🧪 Laboratories and clean rooms

🌿 Greenhouses, climate chambers

🧠 Industrial instrumentation

🏭 HVAC processes and quality control

🚚 Pharmaceutical and food storage