Board description

UM1502

10/23

Doc ID 022625 Rev 1

2.3.2

Setting the pressure reference (zero, 0 mbar)

By pressing the P1 button, the system sets the pressure reference. The pressure reference

is the one read by the MEMS at the moment the button is pressed.

Every time that button P1 is pressed, a new reference is set.

Once the reference is set, the OFS LED turns off, and the lower LED in the LED bar turns

on.

From now on, the pressure signal is also available as PWM modulation (see Section 2.3.3).

2.3.3

Output signals

Once the pressure reference is set, the pressure signal is available as PWM modulation on

connector J3. The signal frequency starts at 43 Hz, meaning 0 mbar. Changes in pressure

modulate the frequency accordingly. An increase of 6 mbar means a decrease of 1 Hz in

frequency change. Therefore, a frequency of 38 Hz means a pressure of 30 mbar.

This frequency range has been adopted to simulate electromechanical pressure sensors. In

this way, it's very easy to replace it with the STEVAL-MKI111V1 demonstration board.

The signals coming from the MEMS sensor are also available on connector J2, although an

external MCU must be connected through the I²C interface.

Additionally, the demonstration board can be connected to an ST debugging tool with SWIM

interface to read in real-time the pressure and temperature data as variables (see also

Section 6).

2.3.4

LED bar

The 5-step LED bar roughly shows the pressure that the MEMS sensor is actually

measuring. Each LED means 6 mbar. Therefore the full range indicated by the LED bar is

30 mbar. In the case of a depression, the LED blinks instead. Therefore the full range shown

by the LED bar is -30 mbar / 30 mbar.