Computer Shopper - UK (2020-10)

ISSUE392|COMPUTER SHOPPER|OCTOBER 2020 93

init.rinit.restypestype=ce=ctypestypes.c_in.c_intt

init.argtypes =[ctypes.c_void_p]init.argtypes =[ctypes.c_void_p]

init(None)init(None)

def SHTC3_Read_Temperature(self):def SHTC3_Read_Temperature(self):

temperature =self.dll.SHTC3_Read_THtemperature =self.dll.SHTC3_Read_TH

temperature.restype =ctypes.c_floattemperature.restype =ctypes.c_float

temperature.argtypes =[ctypes.c_temperature.argtypes =[ctypes.c_

void_p]void_p]

return temperature(None)return temperature(None)

def SHTC3_Read_Humidity(self):def SHTC3_Read_Humidity(self):
humidity =self.dll.SHTC3_Read_RHhumidity =self.dll.SHTC3_Read_RH
humidity.restype =ctypes.c_floathumidity.restype =ctypes.c_float
humidity.argtypes=[ctypes.c_void_p]humidity.argtypes=[ctypes.c_void_p]
return humidity(None)return humidity(None)
offset =10offset =10

if name == "main":if name == "main":
shtc3 =SHTC3()shtc3 =SHTC3()
while True:while True:
time.sleep(5)time.sleep(5)
temp =shtc3.SHTC3_Read_Temperature()temp =shtc3.SHTC3_Read_Temperature()
-offset-offset
humidity =shtc3.SHTC3_Read_Humidity()humidity =shtc3.SHTC3_Read_Humidity()
if shtc3.SHTC3_Read_Humidity() >50:if shtc3.SHTC3_Read_Humidity() >50:
print('It is humid:Humdity =print('It is humid: Humdity =
%6.2f%%' %humidity)%6.2f%%' %humidity)
else:else:
print('It is not humid: Humdity=print('It is nothumid: Humdity=
%6.2f%%' %humidity)%6.2f%%' %humidity)
if shtc3.SHTC3_Read_Temperature() >if shtc3.SHTC3_Read_Temperature() >
30:30:
print('It is hot: Temperature=print('It is hot: Temperature =
%6.2f°C' %temp)%6.2f°C' %temp)
else:else:
print('It is cool: Temperature =print('It is cool: Temperature =
%6.2f°C' %temp)%6.2f°C' %temp)

To explain whatthis code does, the first
import commands add thelibraries that
we’ll need later on. Next, the class section

creates functions thatwill read the

temperatureand humidity when called.

We then create avariable called offset,

which has the difference in the actual

temperaturecompared to the temperature

read fromthe Pi.Weused asmartthermostat

to get the initial difference. To set your own

offset, change thescript so thatthe offset is 0,

then run the script for 20 minutes or so,then

you can compare the temperaturerecorded

by the Pi against the temperatureonan

external thermometer,smartorotherwise.

Ta ke the difference and set this as your offset.

Now,weget into the script. We’ve got a

While loop here,which keeps on running

(you need to press Ctrl-C to cancel it).

We’ve got asleep statement to makethe

script pause for five seconds on each

interaction, although you can makethis

longer if you prefer.

Next, we set avariableastemp,takingthe

current temperatureand subtracting our

offset, and we read the current humidity and

storethis in avariable called humidity.Our

set of If statementsunderneaththen say it’s

humid if the humidity is above 50%, or not

humid if under; and it says if it’s hot if the

temperatureisabove 30oCorcool if it’s

below this. Both statements print thecurrent

temperatureand humidity.

To see the script in action, download our

file and put it on your computer,and then

at the command line typepython tandh.py.

Thescript will run through.

TAKING IT FURTHER

Now thatyou’ve got abasic script working,

you can starttododifferent things with the

settings. Forexample, you can change the If

statements, to alsolook for low temperatures

and low humidity.For example, if you wanted

your Pi to monitor when it was cold, and

thereforeindanger of pipes freezing, you

could look for temperatures below 5oC.

However,wedorecommend upgrading to

the external temperatureprobe for this to

increase accuracy.Likewise, you can make

the script tell you when humidity is low and

it’s time to turn on ahumidifier.

Yo ucan also makethe script interact with

any devices connected to the Pi.For instance,

if you follow our last Raspberry Pi project

guide (available atwww.shopperdownload.

co.uk/pi/piguide.pdf), youcan find outhow

to control LEDs connected to the GPIO.

By customising this script,you canmake

an LED turn on whenthere’shighhumidity as

avisualwarning. Yo ucan even use the

WebHooksservice to connect your Pi to

IFTTT, say turning on asmartplug that

controls ahumidifier automatically or

sending awarning message to your phone.

Theimportant thing is thatwiththe

addition of extrasensors,the Pi can become

awareofits surroundings, letting it react to

real-life changes.

ABOVE:Our script gives you the current temperatureand humidity

LEFT:Youneed to enable the I2Cinterface to

get going with the SenseHAT

PI PROJECTS