| Urs Fleisch | 430400b | 2011-01-07 07:15:39 +0000 | [diff] [blame] | 1 | Kernel driver sht21 |
| 2 | =================== |
| 3 | |
| 4 | Supported chips: |
| 5 | * Sensirion SHT21 |
| 6 | Prefix: 'sht21' |
| 7 | Addresses scanned: none |
| 8 | Datasheet: Publicly available at the Sensirion website |
| 9 | http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf |
| 10 | |
| 11 | * Sensirion SHT25 |
| 12 | Prefix: 'sht21' |
| 13 | Addresses scanned: none |
| 14 | Datasheet: Publicly available at the Sensirion website |
| 15 | http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT25.pdf |
| 16 | |
| 17 | Author: |
| 18 | Urs Fleisch <urs.fleisch@sensirion.com> |
| 19 | |
| 20 | Description |
| 21 | ----------- |
| 22 | |
| 23 | The SHT21 and SHT25 are humidity and temperature sensors in a DFN package of |
| 24 | only 3 x 3 mm footprint and 1.1 mm height. The difference between the two |
| 25 | devices is the higher level of precision of the SHT25 (1.8% relative humidity, |
| 26 | 0.2 degree Celsius) compared with the SHT21 (2.0% relative humidity, |
| 27 | 0.3 degree Celsius). |
| 28 | |
| 29 | The devices communicate with the I2C protocol. All sensors are set to the same |
| 30 | I2C address 0x40, so an entry with I2C_BOARD_INFO("sht21", 0x40) can be used |
| 31 | in the board setup code. |
| 32 | |
| 33 | sysfs-Interface |
| 34 | --------------- |
| 35 | |
| 36 | temp1_input - temperature input |
| 37 | humidity1_input - humidity input |
| 38 | |
| 39 | Notes |
| 40 | ----- |
| 41 | |
| 42 | The driver uses the default resolution settings of 12 bit for humidity and 14 |
| 43 | bit for temperature, which results in typical measurement times of 22 ms for |
| 44 | humidity and 66 ms for temperature. To keep self heating below 0.1 degree |
| 45 | Celsius, the device should not be active for more than 10% of the time, |
| 46 | e.g. maximum two measurements per second at the given resolution. |
| 47 | |
| 48 | Different resolutions, the on-chip heater, using the CRC checksum and reading |
| 49 | the serial number are not supported yet. |