www.sensirion.com / D1

Version 7.1 – March 2025

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Quick Start Guide

A typical application circuit for SHT4x is shown on the left-hand side of Figure 1. After reaching the minimal

supply voltage and allowing for the maximal power-up time of 1 ms the sensor is ready for I2C

communication. The quickest way to measure humidity and temperature is pseudo-coded on the right-hand

side of Figure 1. Together with the conversion formulae given in equations ( 1 ), ( 2 ) & ( 3 )the digital signals

can be translated into relative humidity and temperature readings.

Typical application circuit

Pseudo code

i2c_write(i2c_addr=0x44, tx_bytes=[0xFD])

wait_seconds(0.01)

rx_bytes = i2c_read(i2c_addr=0x44, number_of_bytes=6)

t_ticks = rx_bytes[0] * 256 + rx_bytes[1]

checksum_t = rx_bytes[2]

rh_ticks = rx_bytes[3] * 256 + rx_bytes[4]

checksum_rh = rx_bytes[5]

t_degC = -45 + 175 * t_ticks/65535

rh_pRH = -6 + 125 * rh_ticks/65535

if (rh_pRH > 100):

rh_pRH = 100

if (rh_pRH < 0):

rh_pRH = 0

Figure 1. Typical application circuit (top) and pseudo code (bottom) for easy starting. For details on the signal

cropping in the last four lines see section 4.6.

Find code resources and embedded drivers on: https://github.com/Sensirion/embedded-sht/releases

CAD files are available on SnapEDA:

https://www.snapeda.com/parts/SHT40-AD1B-R3/Sensirion/view-part/