HOW DOES IT WORK?

Pressure 19 Click as its foundation uses the MLX90817, a factory-calibrated absolute pressure sensor delivering ratiometric analog output from Melexis Technologies. The MLX90817 absolute pressure sensor includes a sensing element, analog to digital converter, signal processing part, and digital interface that sends the digital pressure data to the host controller. It measures pressure from 0.2 up to 3bar with pressure accuracy of ±33mbar over a wide operating temperature range at the industry's lowest power.

The MLX90817 contains a pressure sensing element that consists of a diaphragm, which reacts to a change in absolute pressure, realized in the silicon chip by wafer bonding on an etched cavity with a built-in reference vacuum. The internal strain increases, in particular at the border of the diaphragm, where piezo-resistive elements have been implanted into the silicon diaphragm forming a Wheatstone bridge, which acts as a transducer. The front end amplifies the signal from the bridge and performs a coarse offset compensation and an ADC conversion. Then, the DSP executes the compensations over temperature. Furthermore, the digital circuit provides some filtering, the possibility to linearize the pressure signal, and also implements the clamping function, delivering an analog output proportional to the pressure.

The analog output voltage of the MLX90817 can be converted to a digital value using MCP3221, a successive approximation A/D converter from Microchip, using a 2-wire I2C compatible interface, or can be sent directly to an analog pin of the mikroBUS™ socket labeled as AN. Selection can be performed by onboard SMD jumper labeled as AD SEL to an appropriate position marked as AN and ADC. Using MCP3221 and I2C interface, data transfers at rates of up to 100kbit/s in the Standard and 400kbit/s in the Fast Mode.

Since the sensor for operation requires a 5V logic voltage level only, this Click board™ also features the PCA9306 voltage-level translator from Texas Instruments. The I2C interface bus lines are routed to the dual bidirectional voltage-level translator, allowing this Click board™ to work with both 3.3V and 5V MCUs properly.

This Click board™ can operate with both 3.3V and 5V logic voltage levels selected via the VCC SEL jumper. This way, it is allowed for both 3.3V and 5V capable MCUs to use the communication lines properly. However, the Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used, as a reference, for further development.

SPECIFICATIONS