ST AN2799 APPLICATION NOTE

AN2799

Application note

Measuring mains power consumption

with the STM32x and STPM01

Introduction

This document describes a software and hardware solution concerning the STM32x
microcontroller and the STPM01 power meter for measuring mains power consumption and
also provides hardware and firmware guidelines to interface the STPM01 with the STM32x
microcontroller. Figure 1 shows the block diagram of the solution. The system described in
this document is the first “brick” to build a complex system for distributed load management.

Figure 1. Block diagram

AM00076v1

November 2008 Rev 1 1/14

www.st.com

Contents AN2799

Contents

1 File organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 STM32F103xx microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1.1 STPM01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4 Firmware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.1 Power meter object description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.1.1 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.1.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.1.3 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.1.4 Deletion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.2 Hardware abstraction layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.2.1 HAL functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.3 Application interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.3.1 Application interface functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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AN2799 File organization

1 File organization

The following table presents the firmware modules.

Table 1. Firmware modules

File Description

PowerMeterHal.h

PowerMeterHalTypes.h

PowerMeterObj.h

PowerMeterTypes.h

PowerMeterHal.c
PowerMeterObj.c

Meterlayer.h Definitions of application interface types and function prototypes

Meter.c

MeterHal.c

ExampleApp.c Library usage example

2 Hardware

The solution is based on the STM32F103xx in the LQFP64 package with 128 kB of Flash
and 20 kB of SRAM for demonstration purposes, but it can be easily ported on the smaller
STM32F101xx microcontroller family based on the same ARM Cortex™-M3 CPU as well.
The device used to measure the phase AC current is the STPM01 with a current
transformer.

Definitions of power meter hardware abstraction layer types and function
prototypes.

Definitions of power meter abstract objects and types.

Power meter hardware abstraction layer and abstract object
implementation

Application interface and hardware abstraction layer implementation

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Hardware AN2799

2.1 STM32F103xx microcontroller

The following list is a brief description of the features of the STM32F103xx microcontroller.
Please refer to the STM32F103xx datasheet for a more detailed description of the device.

● Core: ARM 32-bit Cortex™-M3 CPU

– 72 MHz, 90 DMIPS with 1.25 DMIPS/MHz

– Single-cycle multiplication and hardware division

● Memory

– 32-to-128 Kbytes of Flash memory

– 6-to-20 Kbytes of SRAM

● Clock, reset and supply management

– 2.0 to 3.6 V application supply and I/Os

– POR, PDR, and programmable voltage detector (PVD)

– 4-to-16 MHz quartz oscillator

– Internal 8 MHz factory-trimmed RC

– Internal 40 kHz RC

– PLL for CPU clock

– 32 kHz oscillator for RTC with calibration

● Low power

– Sleep, stop and standby modes

– VBAT supply for RTC and backup registers

● 2 x 12-bit, 1 µs A/D converters (16-channel)

– Conversion range: 0 to 3.6 V

– Dual-sample and hold capability

– Temperature sensor

● DMA

– 7-channel DMA controller

– Peripherals supported: timers, ADC, SPIs, I

● Debug mode

– Serial wire debug (SWD) & JTAG interfaces

● Up to 80 fast I/O ports

– 26/36/51/80 I/Os, all mappable on 16 external interrupt vectors, all 5 V-tolerant

except for analog inputs

● Up to 7 timers

– Up to three 16-bit timers, each with up to 4 IC/OC/PWM or pulse counter

– 16-bit, 6-channel advanced control timer: up to 6 channels for PWM output dead

time generation and emergency stop

– 2 watchdog timers (independent and window)

– SysTick timer: a 24-bit down counter

● Up to 9 communication interfaces

– Up to 2 I

2

C interfaces (SMBus/PMBus)

2

Cs and USARTs

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AN2799 Hardware

– Up to 3 USARTs (ISO 7816 interface, LIN, IrDA capability, modem control)

– Up to 2 SPIs (18 Mbit/s)

– CAN interface (2.0B Active)

– USB 2.0 full speed interface

● Packages are ECOPACK

®

(RoHS compliant)

2.1.1 STPM01

The STPM01 is a programmable single-phase energy metering IC which is designed for
effective measurement of active, reactive and apparent energy in a power line system using
a Rogowski coil, a current transformer and shunt sensors. The solution presented in this
document is based on a current transformer sensor. The following list is a brief description of
the main features of the STPM01. For more details, please refer to the device datasheet.

● Active, reactive, apparent energies and RMS values

● Ripple-free active energy pulsed output

● Live and neutral monitoring for tamper detection

● Easy and fast digital calibration in only one point over the whole current range

● OTP for calibration and configuration

● Integrated linear V

● Selectable RC or crystal oscillator

● Supports 50-60 Hz - IEC62052-11, IEC62053-2X specification

● Less than 0.1% error

● Precision voltage reference: 1.23 V and 30 ppm/°C max

for digital and analog supply

REGS

2.2 Hardware description

The hardware used in managing the STPM01 by the STM32x microcontroller is described in
this section. Figure 2 shows a reference schematic to interface the STM32x microcontroller
with the STPM01. The STPM01 bidirectional data line is connected to the SPI-MISO of the
STM32. This is because the speeds for the data read and data write operations of the
STPM01 SPI interface are much too different: 32 MHz for the read operation and 100 kHz
for the write operation. In fact during the write operation, the serial communication is
emulated by software to have very slow communication on the STPM01 data line and during
the read operation, the STM32 SPI peripheral is used to reach the maximum speed
possible. Since the maximum speed of the STM32 SPI is 18 MHz, it doesn't matter which
SPI peripheral is used to have the maximum read bit rate. In this application the SPI2 is
used. The STPM01 clock is provided by the PA8 pin configured as the MCO alternate
function. The AC current is provided to the STPM01 by a current transformer connected to
the current channel 1. For more details about analog parts related to the STPM01, please
refer to the STPM01 datasheet.

Note: The solution has been validated using the “SmartPlug” board. For further details please

refer to the “SmartPlug hardware user manual” .

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