UM1502

Board description

Doc ID 022625 Rev 1

7/23

2

Board description

2.1

Block diagram

The water level detection demonstration board can be divided into a few simple blocks.

Figure 2.

STEVAL-MKI111V1 block diagram

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Power supply

The power supply is designed using a low drop positive voltage regulator with fixed

output voltage set at 3.3 V DC. The input voltage is in the range 5-12 V DC. The power

supply is protected against reverse polarity.

●

MEMS sensor

The demonstration board is physically connected to a container through a rubber tube.

The liquid inside the container goes through the rubber tube, pushing the remaining air

against the MEMS sensor. The higher the amount of liquid inside the container, the

higher the amount of pressure the MEMS sensor reads.

The MEMS sensor is also equipped with a temperature sensor. The measure of

temperature can be used to compensate the pressure drift due to temperature

variations.

Note:

To work properly, the MEMS sensor must be mounted higher than the container.

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User interface

The demonstration board features an LED user interface. It roughly shows the pressure

(and depression) read by the MEMS sensor.

The user interface is completed with a debugging connector. It serves to precisely read

the measurements of pressure and temperature in real-time by means of any standard

ST debugging tool with SWIM interface.

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Output signals

The pressure and temperature measurements can be accessed either through an I²C

interface, or by PWM modulation. The signals can be sent to an external MCU through

the I²C interface. Alternatively, the pressure signal is sent out in the form of a 43-38 Hz