In this article we look at another absolute pressure sensor – this time its the LPS22HB
Lets look at the sensor
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.
- 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
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
|Raspberry Pi 4||AliExpress Product|
|LPS22HB pressure sensor||AliExpress Product|
|Dupont Connecting wire||AliExpress Product|
I could not find a fritzing part but this is again an easy sensor to connect to a Raspberry Pi.
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=lps22hb._read_byte(LPS_PRESS_OUT_XL) u8Buf=lps22hb._read_byte(LPS_PRESS_OUT_L) u8Buf=lps22hb._read_byte(LPS_PRESS_OUT_H) PRESS_DATA=((u8Buf<<16)+(u8Buf<<8)+u8Buf)/4096.0 if (lps22hb._read_byte(LPS_STATUS)&0x02)==0x02: # a new pressure data is generated u8Buf=lps22hb._read_byte(LPS_TEMP_OUT_L) u8Buf=lps22hb._read_byte(LPS_TEMP_OUT_H) TEMP_DATA=((u8Buf<<8)+u8Buf)/100.0 print('Pressure = %6.2f hPa , Temperature = %6.2f °C\r\n'%(PRESS_DATA,TEMP_DATA))
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