In this comprehensive article we will configure a system for environmental temperature and pressure measuring and, to do this, we will use an appropriate sensor and Arduino. We will see specifications, schematics, dimensioning, links, code and final results. And then we will evaluate its future implementation. Are you ready?
Measuring the temperature inside a room, seeing how it varies in time and trying to characterize all the rooms of a house depending on whether they are comfortable and liveable in all seasons, has always been an interesting challenge.
It would be very useful to all those who want to understand, for example, how to improve the energy efficiency of their home, dedicating each room to its appropriate use, depending on these characteristics, perhaps discovering that there is no need to change something. The distribution of space, furniture, livability, could transform the house you live in, into a different, perhaps better living experience. This challenge, in fact, can be faced with a relatively more complex system compared to the one we will see today but it, of course, can also be achieved with such a basic device.
2. The sensor
We will use a barometric sensor, the BMP085 of Bosch, which is a low power consumption precise device. The measuring range is from 300 to 1100 hPa with an absolute accuracy equal to 0.03 hPa. For maximum clarity, note that
1 hPa = 1 mbar
1 Pa = 1 N = 1 kg m ^ m ^ -2 s ^ -1 -2
The technology on which it is based allows excellent linearity, high accuracy, but above all, it allows resistance to electromagnetic interference. Another interesting feature is its long-term stability. There is, in fact, no evidence of substantial variation of the functional parameters of the device in function while being used.
The sensor can work with bias voltages between 1.8 V and 3.6 V.
It is designed to be directly connected to a microcontroller that has an I2C input and, in fact, thanks to this type of connection, we will use it for this experiment. The board allows to use a 6 pin header. VDDD and VDDA of the sensor are connected together and lead to a single pin; This is a choice that, in general, may not be good, but which, for our specific application, should not create particular problems.
If the sensor, however, should be incorporated into a more complex system, working with mixed signals, it will certainly be necessary to distinguish digital power supply from analog power supply.
A resistor of 4.7 kΩ is used as a simple network of pull-up. Going back, briefly, to the characteristics, the most interesting are:
- I2C interface;
- wide range of pressure;
- different supply voltages;
- low power consumption (5 uA @ 1 sample / s);
- low measurement noise;
- extremely compact size (16.5 x 16.5 mm).
Let's deal with configuration now; the datasheet immediately shows the configuration method of the sensor, and it involves the use of simple resistors and capacitors to make it operational (Figure 1).
Figure 1: Layout of connection with sensor and microcontroller
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