Introduction

This application note describes the LC sensor metering feature included in the STM32U5 Nucleo board NUCLEO-U575ZI-Q.

The STM32U5 Series microcontrollers combine ultra-low-power with performance, offering a complete set of analog and digital

peripherals. These peripherals can operate in autonomous mode down to Stop 2 mode, a subset of which is used to build

the LC sensor‑based meter. This is the starting point for the implementation of gas or water meter applications, based on the

inductive reading of a rotating mechanical wheel.

The demonstration based on the STM32U5 can be executed with a single USB cable (type A to B) connecting the host PC to

the NUCLEO-U575ZI-Q, and a custom LC sensor board.

This application note is delivered with the X-CUBE-LCSENSOR expansion package dedicated to STM32U5xx microcontrollers

using the STM32CubeMX (6.6.1) tool with the LPBAM interface.

LC sensor metering implementation on STM32U5 Series featuring LPBAM

AN5834

Application note

AN5834 - Rev 1 - December 2022

For further information contact your local STMicroelectronics sales office.

www.st.com

1 General information

The STM32U5 Series microcontrollers are based on the Arm

Cortex

-M33 processor.

Note: Arm is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.

Table 1. Acronyms and terms

Acronym Definition Description

Vmid

Middle voltage (V

/2)

It allows energizing LC sensor. It is delivered by

DAC peripheral output for STM32U5. To save power

consumption, Vmid is disabled when the LC sensor is not

activated.

Vcmp Comparator threshold voltage It is set above Vmid to provide a noise margin.

Texcit Excitation pulse width It allows driving LC sensor in output push-pull.

Tcapture Time to perform the measurement

During this time, the comparator collects oscillations,

compares them to Vcmp and delivers pulses to the low

power timer.

Count Pulse count number

It is generated by the LC sensor and conditioned by the

comparator.

CountDetect

Detection threshold for the count

number

It allows defining the sensor state (metal or no metal).

CountMax

Maximum number of counted pulses,

without metal, in proximity of the LC

sensor

CountMin

Minimum number of counted pulses,

with metal, in proximity of the LC

sensor

Reference documents

[1]

Application note Demonstration of LC sensor for gas or water metering based on STM32L073Z

‑

EVAL and

STM32L476RG

‑

NUCLEO boards (AN4636)

[2] Application note How to build STM32 LPBAM application using STM32CubeMX (AN5816)

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General information

AN5834 - Rev 1

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