08_Temp_Motion.md

08. Temperature/Humidity and Motion Sensors (08_Temp_Motion)

In this exercise we will:

• Connect an actual temperature and humidity sensor (DHT-22).
• Connect an motion sensor (PIR HC-SR501).
• Push sensor readings to the web app.
• Apply some refactor to the previous device code in order to improve the app architecture.

The web app version from 06_JSON_2Relay_App will be used. The device code is in 08_Temp_Motion.

We are using the connections from previous exercise:

ESP GPIO	Port	What
13	1	LED (leg with resistor)
12	2	LED (leg with resistor)
14	3	LED (leg with resistor)
4	4	IN1 from 2-Relay Module
5	5	IN2 from 2-Relay Module

After refactoring

Up until now most of the code was more procedural C than object-oriented C++. Also our solution now is capable of handling many endpoint types.

After refactoring, we have these major classes:

• FeatureController - the core for each of the features our device supports.
• MainApp - is the main device program entry point.
• DeviceContext - access point to relevant objects
• DeviceConfig - stores relevant configuration values.
• JsonSerializationProvider - responsible for serialization of JSON messages.
• HttpMessageBus - responsible for transporting messages between device and message bus over HTTP protocol.

Whenever a new control device or sensor gets added we would have to create (or use) one of the subclasses of FeatureController. We also register the the feature instance inside the MainApp constructor:

// define all the features
_features.push_back(new SwitchFeatureController(4, this, 4, false));
_features.push_back(new SwitchFeatureController(5, this, 5, false));

_features.push_back(new LedFeatureController(1, this, 13));
_features.push_back(new LedFeatureController(2, this, 12));
_features.push_back(new LedFeatureController(3, this, 14));

The FeatureController class has two virtual methods that the subclass can override:

• void Loop() - used to execute logic every run of the device loop. This would include reading sensor data and sending messages with the measurements.
• void Handle(JsonObject& command) - used to handle incoming messages (commands) for this feature instance (port & type match).

Have a look at the SwitchFeatureController.

Running the program

When running the device sketch the Serial Monitor outputs:

[MainApp] Connecting to IoT_Network
..
[MainApp] WiFi connected
[MainApp] IP: 192.168.2.148
[MainApp] Starting...
[MainApp] Sending DeviceDescription...
[HTTP] Connecting to http://iot-remotecontrol-2.azurewebsites.net/api/device/register
[HTTP] Payload: {"deviceId":"my_device_id","features":[{"type":"switch","port":4},{"type":"switch","port":5},{"type":"led","port":1},{"type":"led","port":2},{"type":"led","port
":3}]}
[HTTP] POST... response code: 200, description:
[MainApp] Started.

The device can be controlled from the test web app: http://iot-remotecontrol-2.azurewebsites.net/

New Hardware Part: DHT-22 - Humidity and Temperature Sensor

The DHT-22 is a low cost humidity and temperature sensor with a single wire digital interface. DHT-22 Specs:

• 3.3-6V Input
• 1-1.5mA measuring current
• 40-50 uA standby current
• Humidity from 0-100% RH
• -40 - 80 degrees C temperature range
• +/- 2% RH accuracy
• +/- 0.5 degrees C

DHT-22 pins from left to right:

Pin	Function
1	Vcc - power supply (3.3V)
2	Data - signal
3	NULL (not used)
4	GND

The Data pin needs to be connected to Vcc via a pull up resistor (10K Ohm).

Link to the online store 1 and online store 2.

Library

There are few libraries to work with the DHT-22 sensor. The DHT sensor library from Adafruit works and is well documented.

Open the provided link to view an example how to use it.

Exercise 1

Push humidity/temperature readings to web app:

• Connect the DHT-22 sensor:
  • Use GPIO pin 12 to connect DHT-22 data pin.
  • Connect Vcc to +3.3V voltage.
• Install library via Library Manager: platformio lib install "DHT sensor library".
• Add the relevant DHT22FeatureController class and register an instance in the MainApp constructor.
  • Notice we have one feature controller to measure both temperature and humidity.
  • Use the controller class Loop() method to read the sensor and send out messages to topic sensor.
  • Use port 6.
• Push the data every 10 seconds.
  • Use the TimeUtil::IntervalPassed() method to avoid blocking the application loop.
  • After each 10 second interval send only one humidity or temperature e.g.: 10s, temp, 10s, humidity, 10s, temp, 10s, humidity.
• The web app already understands temperatureSensor and humiditySensor feature types.

To recall from laboratory 06_JSON_2Relay, the temperature/humidity sensor reading JSON are:

{
	"type": "temperatureSensor",
	"port": 6,
	"deviceId": "my_device_id",
	"temperature": 23.5
}

{
	"type": "humiditySensor",
	"port": 6,
	"deviceId": "my_device_id",
	"humidity": 43.4
}

New Hardware Part: PIR HC-SR501 - Motion Sensor

Specs

• 4.5-20V DC Input
• Current 50uA
• Output signal 0,3V or 5V
• Field of view 110 degree
• Max Distance 7m

PIR HC-SR501 pins from left to right:

Pin	Function
1	Vcc - power supply
2	Out - HIGH when movement detected, otherwise LOW
3	GND

The sensor has some customization:

• T1 - duration of HIGH when motion detected.
• T2 - sensitivity of sensor (distance).
• H - (mode) keeps Out HIGH while motion is happening
• L - (mode) keeps Out HIGH only during first movement detection.

Link to the online store 1 and online store 2.

Exercise 2

Push motion events to web app:

• Connect the motion sensor:
  • Use GPIO pin 14 to connect sensor Out pin.
  • Connect Vcc to +3.3V voltage.
• Add the relevant MotionFeatureController class and create and instance inside the MainApp constructor.
  • Use the controller class Loop() method to read the sensor and send out messages to topic sensor.
  • Use port 7.
• Push the data onlu on state change and not often than every 3 seconds.
  • Use the TimeUtil::IntervalPassed() method to avoid blocking the application loop.
• The web app already understands motionSensor feature types.

The motion message that the web app understands:

{
	"type": "motionSensor",
	"port": 7,
	"deviceId": "my_device_id",
	"motion": true
}

Make sure to send this message to the sensor topic (same as for the temperature/humidity readings).