Integration of sensors

Prototyping area

The prototyping area included within the board is divided into two regions: the pads area and the integrated circuits area.

Pads 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.

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.

Integrated circuits area

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.

Analog-to-Digital Converter

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.

Basic reading code:

{
	 float value;
	 SensorProtov20.ON();
	 delay(10);
	 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/

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