Integration of sensors
The prototyping area included within the board is divided into two regions: the pads area and the integrated circuits area.
This is a matrix of 16x8 pads of 1 mm diameter whose aim is to fit discrete components such as resistors, capacitors or DIP encapsulated integrated circuits. The metallised area of each pad is of a larger size to facilitate both welding the components to the pads and welding pads to each other.
On the upper part and the lower part of the matrix there are strips of pads that provide an output to all the mote's signals in the sensors' connectors. In the next figure and its adjoining table we can see which microprocessor pin corresponds to each pad.
Figure : Image of the Waspmote inputs and outputs
Digital input/output signal DIGITAL8
Digital input/output signal DIGITAL6
Digital input/output signal DIGITAL4
Digital input/output signal DIGITAL2
Digital input/output signal and analog input ANALOG6
Digital input/output signal and analog input ANALOG4
Digital input/output signal and analog input ANALOG2
3.3 V Power Supply (SENS_PW_3V3)
3.3 V Power Supply (GPS_PW)
SDA (I2C bus signal)
SCL (I2C bus signal)
5 V Power Supply (SENS_PW_5V)
Digital input/output signal and analog input ANALOG1
Digital input/output signal and analog input ANALOG3
Digital input/output signal and analog input ANALOG5
Digital input/output signal and analog input ANALOG7
Digital input/output signal DIGITAL1
Digital input/output signal DIGITAL3
Digital input/output signal DIGITAL5
Digital input/output signal DIGITAL7
Transmission Output UART 1 SERIAL_1_TX
Reception Input UART 1 SERIAL_1_RX
Reception Input UART 2 SERIAL_2_RX
Transmission Output UART 2 SERIAL_2_TX
Battery Supply Voltage
SCK (SPI bus signal)
High interrupt input signal RXD1
Low interrupt input signal TXD1
3.3V Supply Voltage (SENS_PW_3V3)
MOSI (SPI bus signal)
MISO (SPI bus signal)
Finally a series of pads connected to the 3.3 V supply, the 5 V supply and to ground are included. They can be seen in the folowing figure.
Figure : Image of the different power supply pads
Seven footprints have been added for SMD integrated circuits of different sizes: One 20 port SO type, one 24 port TSSOP, one 10 port micro-SOIC, two 6 port SOT-23 and two 6 port SC-70. Output is given to each of the footprint ports through a 1mm diameter pad, from which it is possible to access the circuit. In the next 2 figures all the integrated circuit footprints and the pads which correspond to their output ports can be seen.
Figure : Image of the SO, TSSOP and SOT-23 circuit area
Figure : Image of the micro-SOIC and SC-70 circuit area
The Waspmote microcontroller incorporates a 10-bit analog-to-digital converter which can be accessed through any of the analog inputs within the main 2x12 pin connector. In the event of any application requiring a higher resolution, a 16-bit Sigma-Delta (ΣΔ) analog-to-digital converter has been added to the prototyping board, with a maximum conversion time of 23 ms (Linear model LTC2453). Communication with this device is carried out through the I2C, allowing a differential reading between its input IN+ and IN- (see section "API" about the board libraries for information on the necessary commands for communication).
Each of the inputs allows a range of voltage between 0 and 4.5 V, allowing therefore a differential measurement between -4.5V and 4.5 V. To obtain a more precise reading, the reference voltage for the conversion is fixed by a voltage reference of 4.5 V, model MAX6107. In the figure below there is a diagram of the connections which follow the converter circuit, and in the following figure the pads from which this is accessed can be seen.
Figure : Diagram of the integration of the analog-to-digital converter
Basic reading code:
value = SensorProtov20.readADC();
You can find a complete example code for reading the analog-to-digital converter at: https://development.libelium.com/prototyping-reading-the-adc/
Figure : Input pins to the analog-to-digital converter