Detailed Sensor Information
This project uses three different types of sensors to collect information about the weather. Each sensor uses it's own way of communicating with the micro controller and its own way of measuring the weather conditions. Below is some detailed information about each sensor and the protocol that it uses to transmit data.
DHT22 - Temperature and Humidity Sensor
This sensor uses a fairly simple way of measuring temperature and humidity.
Temperature is measured using a thermistor, which is a special type of resistor whose resistance changes based on the temperature. Humidity is measured using capacitance. This works by placing a thin strip of metal oxide between two electrodes. The capacitance of the metal changes as the humidity changes.
​
To communicate with the micro controller, this sensor uses a digital output. This means that, put simply, the sensor takes the readings that it collects and converts them into 1s and 0s. Then, those bits are sent to a micro controller pin configured to accept a digital input.
BMP 180 - Barometric Pressure Sensor
This sensor can give a barometric pressure reading and altitude reading by measuring the air pressure at any given point in time. The way that this sensor measures air pressure is with a small metal box that has had the air sucked out of it. As the air pressure changes, the metal on the box expands and contracts. The sensor can calculate the air pressure by measuring these changes.
​
To communicate with the micro controller, this sensor uses the I2C protocol. This protocol uses two pins to communicate, the SDA and SCl pins. The SDA pin is the data transfer pin and the SCL is the clock pin. One device is marked as the master device and one is marked as the slave. In this case, the sensor is the slave and the micro controller is the master. The master controls the clock signal and listens for when the slaves connected to it send data at the clock speed. When a message is detected, the data is transmitted to the micro controller.
Modern Device Wind Sensor
This sensor measures wind speed using the "hot wire" method. Typically, wind speed is measured using an anemometer with spinning cups, but this sensor uses a method that involves heating up an element on the board and maintaining that temperature using a voltage. When the wind blows, the voltage must increase to maintain the constant temperature. From the voltage change, wind speed can be calculated.
​
This sensor uses an analog signal to transmit data to the micro controller. This means that the sensor sends a signal that varies in voltage to a pin on the micro controller that is expecting this protocol. That voltage is converted to a value that can be used.
​
