www.sensirion.com / D1

Version 2

– July 2021

3/17

1 Quick Start

– Hello World

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 ), and ( 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 (left) and pseudo code (right) for easy starting. For details on

the signal cropping in the last four lines see section 4.5.

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

sht/releases

CAD files can be downloaded from SnapEDA: https://www.snapeda.com/parts/SHT40-AD1B-

R3/Sensirion/view-part/