1 Kernel driver sht21 1 Kernel driver sht21
2 =================== 2 ===================
3 3
4 Supported chips: 4 Supported chips:
5 5
6 * Sensirion SHT21 6 * Sensirion SHT21
7 7
8 Prefix: 'sht21' 8 Prefix: 'sht21'
9 9
10 Addresses scanned: none 10 Addresses scanned: none
11 11
12 Datasheet: Publicly available at the Sensi 12 Datasheet: Publicly available at the Sensirion website
13 13
14 https://www.sensirion.com/file/datasheet_s 14 https://www.sensirion.com/file/datasheet_sht21
15 15
16 16
17 17
18 * Sensirion SHT25 18 * Sensirion SHT25
19 19
20 Prefix: 'sht25' 20 Prefix: 'sht25'
21 21
22 Addresses scanned: none 22 Addresses scanned: none
23 23
24 Datasheet: Publicly available at the Sensi 24 Datasheet: Publicly available at the Sensirion website
25 25
26 https://www.sensirion.com/file/datasheet_s 26 https://www.sensirion.com/file/datasheet_sht25
27 27
28 28
29 29
30 Author: 30 Author:
31 31
32 Urs Fleisch <urs.fleisch@sensirion.com> 32 Urs Fleisch <urs.fleisch@sensirion.com>
33 33
34 Description 34 Description
35 ----------- 35 -----------
36 36
37 The SHT21 and SHT25 are humidity and temperatu 37 The SHT21 and SHT25 are humidity and temperature sensors in a DFN package of
38 only 3 x 3 mm footprint and 1.1 mm height. The 38 only 3 x 3 mm footprint and 1.1 mm height. The difference between the two
39 devices is the higher level of precision of th 39 devices is the higher level of precision of the SHT25 (1.8% relative humidity,
40 0.2 degree Celsius) compared with the SHT21 (2 40 0.2 degree Celsius) compared with the SHT21 (2.0% relative humidity,
41 0.3 degree Celsius). 41 0.3 degree Celsius).
42 42
43 The devices communicate with the I2C protocol. 43 The devices communicate with the I2C protocol. All sensors are set to the same
44 I2C address 0x40, so an entry with I2C_BOARD_I 44 I2C address 0x40, so an entry with I2C_BOARD_INFO("sht21", 0x40) can be used
45 in the board setup code. 45 in the board setup code.
46 46
47 sysfs-Interface 47 sysfs-Interface
48 --------------- 48 ---------------
49 49
50 temp1_input 50 temp1_input
51 - temperature input 51 - temperature input
52 52
53 humidity1_input 53 humidity1_input
54 - humidity input 54 - humidity input
55 eic 55 eic
56 - Electronic Identification Code 56 - Electronic Identification Code
57 57
58 Notes 58 Notes
59 ----- 59 -----
60 60
61 The driver uses the default resolution setting 61 The driver uses the default resolution settings of 12 bit for humidity and 14
62 bit for temperature, which results in typical 62 bit for temperature, which results in typical measurement times of 22 ms for
63 humidity and 66 ms for temperature. To keep se 63 humidity and 66 ms for temperature. To keep self heating below 0.1 degree
64 Celsius, the device should not be active for m 64 Celsius, the device should not be active for more than 10% of the time,
65 e.g. maximum two measurements per second at th 65 e.g. maximum two measurements per second at the given resolution.
66 66
67 Different resolutions, the on-chip heater, and 67 Different resolutions, the on-chip heater, and using the CRC checksum
68 are not supported yet. 68 are not supported yet.
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