Integration Of New Sensors - Libelium Waspmote Technical Manual

Sensors

8.2. Integration of new sensors

The Waspmote design is prepared for the integration of both input (sensors) and output (actuators) which allows
to grow the wide range of existing Waspmote sensor boards. The new sensors can be connected to Waspmote's
2x12 and 1x12 pin connectors, which permit to use 16 input and output signals, 7 of which can be used as analog
inputs and 1 as a PWM (Pulse Width Modulation) output signal. Besides, there is a line to ground, 3.3 V and 5 V
power feeds, 2 selectable connections to the serial communication (UART) inputs and outputs, connection to the
2 lines of the (I2C) SCL and SDA Inter-Integrated Circuit bus, and connection to inputs for high level and low level
interrupt. An image of the Waspmote output connectors can be seen in the "I/O" section.
The management the 2 power lines (3.3 and 5 V) for the sensor boards (described in more depth in section
"Sensors" → Power) is carried out through 2 solid state switches which allow the continuous flow of a current of up
to 200 mA and whose control can be programmed using the functions included in the WaspPWR library, described
in the files WaspPWR.h and WaspPWR.cpp.
The input and output voltage values for both digital and analog pins will be between 0 V and 3.3 V, logic zero ('0')
being found in values less than 0.5 V and logic one ('1') in values higher than 2.30 V. To read analog signals, the
microcontroller has a 10-bit analog-to-digital converter which allows a resolution of 3 mV. Waspmote also has one
8-bit resolution PWM output pin for the generation of analog signals. Information on the libraries and instructions
used for reading and writing on these pins can be found in the API manual.
Waspmote includes 2 interruption pins, a low level (TXD1) one and a high level (RXD1) one, which offer an
alternative to reading the sensors by survey, allowing the microcontroller to be woken up when an event occurs
(such as exceeding a certain threshold in a comparator) which generates a change in a digital signal connected to
one of the above pins, facilitating the sensor reading only at the moments when a remarkable event occurs.
This option is especially recommended for low consumption sensors that may remain active for long periods of
time. Reading by survey (switched on and cyclical sensor reading after a set time) is more appropriate for those
that, in addition to showing greater consumption, do not require monitoring that generates an alarm signal.
The interruptions can be managed using the warning functions and vectors (flags) defined in the Winterruptions
library, file Winterruptions.c. More can be learnt about their use in the Interruption Programming Guide.
Sensors reading can generate 3 types of response: storage of collected data (on the SD card), wireless transmission
of data (via wireless module) or automatic activation through an actuator directly controlled by the microcontroller's
output signals or through a switch or relay.
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