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SDP810_500pa_example.py
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SDP810_500pa_example.py
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#Reading the Sensirion SDP810 500PA sensor
#Dev by JJ SlabbertSDP810_example
#Code tested with Python 2.7
#Run sudo i2cdetect -y 1 in the terminal, to see if the sensor is connected. it will show address 25
#Check the datasheet at https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/0_Datasheets/Differential_Pressure/Sensirion_Differential_Pressure_Sensors_SDP8xx_Digital_Datasheet.pdf
#The sensor i2c address is 0x25 (Not user Programable).
#I have no formal electronics, physics or programing education, code should be tested before critical applications
import smbus
import time
bus=smbus.SMBus(1) #The default i2c bus
address=0x25
bus.write_i2c_block_data(address, 0x3F, [0xF9]) #Stop any cont measurement of the sensor
time.sleep(0.8)
#Start Continuous Measurement (5.3.1 in Data sheet)
print ("(Start Continuous Measurement (5.3.1 in Data sheet)")
##Command code (Hex) Temperature compensation Averaging
##0x3603 Mass flow Average till read
##0x3608 Mass flow None Update rate 0.5ms
##0x3615 Differential pressure Average till read
##0x361E Differential pressure None Update rate 0.5ms
# We will use command code 0x3603 (Mass flow, Average till read)
#the smbus write_i2c_block_data function have 3 arguments, addr=the i2c address, cmd and [val]. cmd and val is derived from the
#Command code in Hex
#We will take 5 readings now
bus.write_i2c_block_data(address, 0x36, [0X03]) # The command code 0x3603 is split into two arguments, cmd=0x36 and [val]=0x03
print ("Taking 5 readings of 9 bites each. See table in section 5.3.1 of datasheet for meaning of each bite")
for x in range (0, 5):
time.sleep(2)
reading=bus.read_i2c_block_data(address,0,9)
print (reading)
#We will now take 5 Diffirential Presure readings
print("We will now take 5 Diffirential Pressure readings, Play around, increase the number of readings, \nblow a fan on one of
the pipes")
for x in range (0, 5):
time.sleep(2)
reading=bus.read_i2c_block_data(address,0,9)
pressure_value=reading[0]+float(reading[1])/255
if pressure_value>=0 and pressure_value<128:
diffirential_pressure=pressure_value*60/256 #scale factor adjustment
elif pressure_value>128 and pressure_value<=256:
diffirential_pressure=-(256-pressure_value)*60/256 #scale factor adjustment
elif pressure_value==128:
diffirential_pressure=99999999 #Out of range
print("Diffirential Pressure: "+str(diffirential_pressure)+" PA")
#We will now take 5 Temperature readings
print("We will now take 5 Temperature readings, Play around, increase the number of readings, Blow a hair dryer on it.")
for x in range (0, 5):
time.sleep(2)
reading=bus.read_i2c_block_data(address,0,9)
temp_value=reading[3]+float(reading[4])/255
if temp_value>=0 and temp_value<=100:
temperature=temp_value*255/200 #scale factor adjustment
if temp_value<=256 and temp_value>=200:
temperature=-(256-temp_value)*255/200 #scale factor adjustment
print("Temperature: "+str(temperature)+" Degrees Celcius")