Include simple example programme demonstrating basic periodic data ac…

…quisition usage.

README.rst

@@ -63,14 +63,12 @@ And then you can start measuring the temperature and humidity:
     print(sensor.temperature)
     print(sensor.relative_humidity)
 
-You can instruct the sensor to start periodically measuring the temperature
-and humidity at a set interval and retrieve the stored measurements:
+You can instruct the sensor to periodically measure the temperature and
+humidity, storing the result in its internal cache:
 
 .. code:: python
 
     sensor.mode = 'Periodic'
-    print(sensor.temperature)
-    print(sensor.relative_humidity)
 
 You can adjust the frequency at which the sensor periodically gathers data to:
 0.5, 1, 2, 4 or 10 Hz. The following adjusts the frequency to 2 Hz:
@@ -79,9 +77,16 @@ You can adjust the frequency at which the sensor periodically gathers data to:
 
     sensor.frequency = 2
 
-
 The sensor is capable of storing eight results. The sensor stores these
-results in an internal FILO cache.
+results in an internal FILO cache. Retrieving these results is simlilar to
+taking a measurement. The sensor clears its cache once the stored data is read.
+The sensor always returns eight data points. The list of results is backfilled
+with the maximum output values of 130.0 ºC and 100.01831417975366 % RH:
+
+.. code:: python
+
+    print(sensor.temperature)
+    print(sensor.relative_humidity)
 
 The sensor will continue to collect data at the set interval until it is
 returned to single shot data acquisition mode:

examples/sht31d_periodictest.py

@@ -0,0 +1,30 @@
+#!/usr/bin/python3
+import time
+import board
+import busio
+import adafruit_sht31d
+
+# Create library object using our Bus I2C port
+i2c = busio.I2C(board.SCL, board.SDA)
+sensor = adafruit_sht31d.SHT31D(i2c)
+
+print('\033[1mSensor\033[0m = SHT31-D')
+print('\033[1mSerial Number\033[0m = ', sensor.serial_number, '\n')
+sensor.frequency = 1
+sensor.mode = 'Periodic'
+for i in range(3):
+    if i == 2:
+        sensor.heater = True
+    if i == 1:
+        time.sleep(4)
+        print('\033[91mCache half full.\033[0m')
+    else:
+        time.sleep(8)
+    if sensor.heater:
+        print('\033[1mHeater:\033[0m On')
+        sensor.heater = False
+    print('\033[1mTemperature:\033[0m ', sensor.temperature)
+    if not sensor.heater:
+        print('\033[1mHeater:\033[0m Off')
+    print('\033[1mHumidity:\033[0m ', sensor.relative_humidity, '\n')
+sensor.mode = 'Single'