Smart Metering

Today things are made smart and processes are becoming smart which enhances the life style of humans in many ways. One such example is the “Smart Metering”. All over the world, the mechanical energy meters are replaced by digital energy meters and currently advanced to smart meters which provide accurate results for greater period of time.

Digital energy meter is an electronic device that measures and stores the consumption of electric energy periodically and communicates the stored information to the provider (utility) via wired communication (Optical port, serial communication) as well as wirelessly for monitoring, analysis and billing. The wireless energy meters are referred as Smart Meters and most commonly used in industrial segments for various reasons and low end energy meters (wired communication) are used in domestic, commercial segments which supports digital interface such as RS232, RS485 serial communication.

Advanced Metering Infrastructure

Since the smart meters include wireless communication such as GSM/GPRS, low power radio, etc the readings can be updated in the central database from anywhere in the world and facilitates the customer (User) with plenty of information’s such as daily usage, peak demand, last interval demand, load profile, voltage profile, sag and swell events, phase information, power factor, tamper notifications, etc. This type of system is named as “Advanced Metering Infrastructure“(AMI). Such a huge amount of information is more important in building a smart grid by which the amount of power generation can be predicted based on power demands.

Automatic Meter Reading

Smart meters with AMI system are more advanced and expensive which makes them overrated for domestic segments. Similar to the “Advanced Metering Infrastructure” (AMI), Automatic Meter Reading (AMR) system is available as an automated way to collect basic meter reading from low end energy meters that are widely used in domestic segments where a system is required for collection only. AMR includes a handheld reading entry device where data from Smart Meters is acquired by connecting the device to the digital ports typically RS232 or RS485 serial ports using dedicated serial cables. The technician will have to plug these cables to the meter of concern and the handheld device will acquire the readings automatically. Likewise the technician will acquire data from each and every meter of his zone and the acquired readings are transferred to the central database for billing.

Though AMR has become common way of reading meters, it can be made more advanced. At present there are many wireless technologies available for small data transfer at very low costs. Among the various wireless technologies, BLE is the most popular. With the BLE enabled smart phones together with an Android app will simply replace the handheld AMR system which performs the similar functionality with wireless operation. Also a tiny BLE module with serial interface (RS232) like eStorm-B1 is sufficient to enable wireless connectivity for the energy meters.

Smart Metering using eStorm-B1 BLE Module

In previous blog, we have discussed in detail about eStorm-B1 BLE module application as a UART to BLE Bridge with a brief demo video. In this blog, we will demonstrate a Smart Metering application which can be realized by interfacing eStorm-B1 with energy meter via RS232 interface and by replacing the traditional handheld reading device with Smart AMR Android app running in Android smart phone with BLE connectivity.

The following video shows the demo of Smart Metering application,

In this demo, a digital energy meter is upgraded to a smart meter by adding eStrom-B1, an NXP KW31Z based BLE module via already available RS232 serial interface. In the other end, an Android Smart phone is equipped with a custom designed Android application “SMART AMR” which will communicate with the smart meter via BLE connectivity and acquire the reading when required.

The following are the features of Smart AMR Android application,

  1. Secured login – User name and password protection for authorized person login only
  2. Area selection – User configurable settings for selecting region, circle and section of his/her zone
  3. GPS based location mapping – Automatic mapping of the user’s present location
  4. One touch reading acquisition – Complete list of available registered meters in the particular location with complete details such as consumer name, ID, meter number, phase, load information and one touch acquisition of old, new reading and energy consumption.
  5. Auto update – Automatic update of acquired readings to central database via available 3G/4G connectivity in Smartphone.

This type of setup is very much suitable for AMR systems which can replace the handheld systems with the low cost smart phones and can reduce the burden on technicians by reducing more physical works that are present in the current handheld systems.

About Embien: Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects like based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.

As a continuation of our previous discussion about selection criteria of BLE SoC for building BLE based IoT devices, we will discuss in detail about the most important considerations for BLE RF layout design and antenna selection from various types available. The communication range of a wireless device with a current limited power source depends mainly on the RF layout, antenna design, and enclosure. Increased operating distance can be achieved with the type of antenna chosen together with carefully designed RF layout with few matching components to ensure most of the power from the BLE SoC reaches the antenna. The more power an antenna can transmit from the SoC, the larger the distance it can cover.

RF layout

RF layout involves routing the transmission lines from BLE SoC to antenna with few matching components in between. RF transmission lines acts as a medium that carry RF power from a BLE SoC to antenna, hence they need to be routed with many constraints to get maximum RF power delivery to antenna. There are several types of transmission lines, the two most popular types are:

  1. Microstrip Line
  2. Coplanar wave guide (CPWG)

Both of these are PCB traces differing in how they are constructed for maintaining the 50-ohm characteristic impedance. There are online calculators available which help us to calculate the impedance of the transmission based on our parameter input.

Microstrip Line – This type of transmission line has a signal trace on top of a substrate with a ground plane beneath the substrate. A microstrip line is simple to construct, simulate, and fabricate. The characteristic impedance of a Microstrip line depends on the following factors,

  1. Substrate height (H)
  2. Dielectric constant of the substrate (εr)
  3. Width of the trace (W)
  4. Thickness of the RF trace (T)
Transmission Line type

MicroStrip Line

CPWG – This is similar to the microstrip, but it has a copper pouring on either side of the RF trace with a gap between them. It provides better isolation for RF traces and a better EMI performance and makes it easier to support the grounding of matching components on an RF trace. The characteristic impedance of a CPWG depends on the following factors:

  1. Substrate height (H)
  2. Dielectric constant of the substrate (εr)
  3. Width of the trace (W)
  4. The gap between the trace and the adjacent ground fill (G)
  5. Thickness of the RF trace (T)
Transmission Line type

Coplanar Wave Guide

Nowadays the SoC manufacturers provide reference designs from which we get the guidelines for routing the RF transmission lines and the values (typically capacitance and inductance values) of the matching components. The designer in addition to the routing guidelines must also note the recommended PCB stackups for desired performances, since the impedance of the RF lines will change depending on the PCB layers stackups. In most of the cases, the PCB fabricator may not match the exact stackup as recommended and at these conditions there will be a need for slight changes in the RF trace width, gaps or thickness to ensure the correct impedance value.

Antenna Types

Antenna is a critical part of any wireless devices that transmits and receives electromagnetic radiation in free space. Antenna is nothing but a conductor exposed in space. When the length of a conductor is a certain multiple or ratio of the wavelength of the signal (λ) it behaves like an antenna and radiates the electrical energy into free space in the form of electromagnetic radiation of that frequency to free space. BLE device range requirement, costs and form factor are the main factors to be considered for choosing the antenna. For BLE applications (2.4GHz), most common types of PCB antennas are as follows,

  1. Wire antenna
  2. PCB Trace Antenna
  3. Chip antenna
  • Wire antenna: It is a piece of wire rise from PCB plane and protrudes to free space over a ground plane. Wire antenna produces best performance and RF range due to its dimension and better exposure. They can be in different forms such as straight wire, helix, loop, etc. A through-hole pad is sufficient to solder the wire antenna, thus saving the board dimension and hence low PCB cost.
Type of Wire antenna

Wire Antenna – Straight and Helix Type

  • PCB antenna: This is a copper trace drawn on the PCB. These antennas are inexpensive and easy to design, because they are a part of the PCB and provide good performance. Meandered trace, inverted F-trace is the most popular PCB antenna’s used in many designs. Meandered trace antenna is recommended for applications that require a minimum PCB area and Inverted F antenna is better compared to meandered antenna for radiation, but it requires space higher than meandered antenna. Main drawback of PCB antenna is that, it may require two or more revision to get expected range performance. This can be avoided by using the antenna design application notes and stack up recommended by the chip vendors carefully.
Types of PCB Antennas

PCB Antenna Types

  • Chip antenna: For applications where the PCB size is to be extremely small, chip antenna is a good choice. They are commercially off the shelf antennas that occupy very small PCB area and offers reasonable performance. But the disadvantage of chip antenna is the increased BoM and assembly cost since they are external components that need to be purchased and assembled. Also the chip antennas are very sensitive to RF ground clearance and the manufacturers RF ground clearance recommendations must be followed strictly.
Types of BLE Antenna

Chip Antenna

There are some applications which need antenna’s to be placed on or outside the enclosure for better reach. In such conditions, there are options for providing antenna connectors on board and extending the connection to the external antenna or other mating connector through shielded wire.

Types of external antenna connection

Antenna Connectors

  • U.FL connector: There are miniaturized RF connectors for high frequency signals. The male connectors are generally surface mounted and soldered directly to the PCB. The female connectors are crimped at one end of the shielded wire and the other end may be a PCB antenna or a mating connector such as SMA, MMCX, etc.
Type of antenna connector

U.FL Connectors

  • MMCX connector: These are Micro-Miniature Coaxial connector. They have a lock-snap mechanism which allows 360 degree rotation. It is comparatively better than U.FL in terms of insertion and removal lifetime and has over 10 times that of U.FL connectors. They are also available in surface mount package.
Type of MMCX connectors and cables

MMCX Connector

About Embien

Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects like based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.