In this article we look at another absolute pressure sensor – this time its the LPS22HB
Lets look at the sensor
Sensor Information
The LPS22HB is an ultra-compact piezoresistive absolute pressure sensor which functions as a digital output barometer. The device comprises a sensing element and an IC interface which communicates through I2C or SPI from the sensing element to the application.
The sensing element, which detects absolute pressure, consists of a suspended membrane manufactured using a dedicated process developed by ST.
The LPS22HB is available in a full-mold, holed LGA package (HLGA). It is guaranteed to operate over a temperature range extending from -40 °C to +85 °C. The package is holed to allow external pressure to reach the sensing element.
Features
- 260 to 1260 hPa absolute pressure range
- Current consumption down to 3 μA
- High overpressure capability: 20x full-scale
- Embedded temperature compensation
- 24-bit pressure data output
- 16-bit temperature data output
- ODR from 1 Hz to 75 Hz
- SPI and I²C interfaces
- Embedded FIFO
- Interrupt functions: Data Ready, FIFO flags, pressure thresholds
- Supply voltage: 1.7 to 3.6 V
- High shock survivability: 22,000 g
Parts Required
Here are the parts required to build this, there are various links you can choose from – I personally buy from Aliexpress as it is usually cheaper but you will probably have to wait 3+ weeks
| Name | Link |
| Raspberry Pi 4 | AliExpress Product |
| LPS22HB pressure sensor | AliExpress Product |
| Dupont Connecting wire | AliExpress Product |
Schematic/Connection
I could not find a fritzing part but this is again an easy sensor to connect to a Raspberry Pi.
| Raspberry Pi | Sensor |
| 3.3v | 3.3v |
| Gnd | Gnd |
| SDA | SDA |
| SCL | SCL |
Code Example
I copied the following code into the thonny ide and ran it
#!/usr/bin/python
# -*- coding:utf-8 -*-
import time
import smbus
#i2c address
LPS22HB_I2C_ADDRESS = 0x5D
#
LPS_ID = 0xB1
#Register
LPS_INT_CFG = 0x0B #Interrupt register
LPS_THS_P_L = 0x0C #Pressure threshold registers
LPS_THS_P_H = 0x0D
LPS_WHO_AM_I = 0x0F #Who am I
LPS_CTRL_REG1 = 0x10 #Control registers
LPS_CTRL_REG2 = 0x11
LPS_CTRL_REG3 = 0x12
LPS_FIFO_CTRL = 0x14 #FIFO configuration register
LPS_REF_P_XL = 0x15 #Reference pressure registers
LPS_REF_P_L = 0x16
LPS_REF_P_H = 0x17
LPS_RPDS_L = 0x18 #Pressure offset registers
LPS_RPDS_H = 0x19
LPS_RES_CONF = 0x1A #Resolution register
LPS_INT_SOURCE = 0x25 #Interrupt register
LPS_FIFO_STATUS = 0x26 #FIFO status register
LPS_STATUS = 0x27 #Status register
LPS_PRESS_OUT_XL = 0x28 #Pressure output registers
LPS_PRESS_OUT_L = 0x29
LPS_PRESS_OUT_H = 0x2A
LPS_TEMP_OUT_L = 0x2B #Temperature output registers
LPS_TEMP_OUT_H = 0x2C
LPS_RES = 0x33 #Filter reset register
class LPS22HB(object):
def __init__(self,address=LPS22HB_I2C_ADDRESS):
self._address = address
self._bus = smbus.SMBus(1)
self.LPS22HB_RESET() #Wait for reset to complete
self._write_byte(LPS_CTRL_REG1 ,0x02) #Low-pass filter disabled , output registers not updated until MSB and LSB have been read , Enable Block Data Update , Set Output Data Rate to 0
def LPS22HB_RESET(self):
Buf=self._read_u16(LPS_CTRL_REG2)
Buf|=0x04
self._write_byte(LPS_CTRL_REG2,Buf) #SWRESET Set 1
while Buf:
Buf=self._read_u16(LPS_CTRL_REG2)
Buf&=0x04
def LPS22HB_START_ONESHOT(self):
Buf=self._read_u16(LPS_CTRL_REG2)
Buf|=0x01 #ONE_SHOT Set 1
self._write_byte(LPS_CTRL_REG2,Buf)
def _read_byte(self,cmd):
return self._bus.read_byte_data(self._address,cmd)
def _read_u16(self,cmd):
LSB = self._bus.read_byte_data(self._address,cmd)
MSB = self._bus.read_byte_data(self._address,cmd+1)
return (MSB << 8) + LSB
def _write_byte(self,cmd,val):
self._bus.write_byte_data(self._address,cmd,val)
if __name__ == '__main__':
PRESS_DATA = 0.0
TEMP_DATA = 0.0
u8Buf=[0,0,0]
print("\nPressure Sensor Test Program ...\n")
lps22hb=LPS22HB()
while True:
time.sleep(0.1)
lps22hb.LPS22HB_START_ONESHOT()
if (lps22hb._read_byte(LPS_STATUS)&0x01)==0x01: # a new pressure data is generated
u8Buf[0]=lps22hb._read_byte(LPS_PRESS_OUT_XL)
u8Buf[1]=lps22hb._read_byte(LPS_PRESS_OUT_L)
u8Buf[2]=lps22hb._read_byte(LPS_PRESS_OUT_H)
PRESS_DATA=((u8Buf[2]<<16)+(u8Buf[1]<<8)+u8Buf[0])/4096.0
if (lps22hb._read_byte(LPS_STATUS)&0x02)==0x02: # a new pressure data is generated
u8Buf[0]=lps22hb._read_byte(LPS_TEMP_OUT_L)
u8Buf[1]=lps22hb._read_byte(LPS_TEMP_OUT_H)
TEMP_DATA=((u8Buf[1]<<8)+u8Buf[0])/100.0
print('Pressure = %6.2f hPa , Temperature = %6.2f °C\r\n'%(PRESS_DATA,TEMP_DATA))Output
In the shell window I saw the following
Pressure = 953.48 hPa , Temperature = 17.19 °C
Pressure = 945.53 hPa , Temperature = 17.19 °C
Pressure = 950.85 hPa , Temperature = 22.05 °C
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