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May 2013 DocID18304 Rev 1 1/38
AN3322
Application note
Watt-hour meter based on the STM32F101 microcontroller
By Ludek Holoubek
Introduction
This document describes, in detail, the hardware and software implementation of a watt-
hour meter using the STM32F101 microcontroller. This cost effective watt-hour meter uses
shunt with an operational amplifier as a current sensor, an embedded 12-bit ADC for current
and voltage measurement, GPIO for LCD management, and a lot of other peripherals for
communication, tamper detection, keyboard, and power disconnection. Powerful
architecture of the STM32™ microcontroller allows sampling at 1 Msps. The high sampling
rate makes it possible to use methods for ADC resolution enhancement.
Main features
Metrological parts
– Microcontroller and external op amp only
– Compliant with EN 50470-1:2006 Class B, precision better than 1%
– Starting current 20 mA, nominal current 5 A, maximum current 100 A
– Reads the voltage and the current signal up to the 21
st
harmonic
– Shunt as a current sensor. CT and Rogowski coil is optional
Additional parts included in reference design
– LCD driven directly by microcontroller
– Keyboard driven directly by microcontroller
– An extra external EEPROM for user data
– Bi-stable relay, IR communication, serial communication
– Backup battery, complete power meter power management
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