About Circuit Cellar Staff

Circuit Cellar's editorial team comprises professional engineers, technical editors, and digital media specialists. You can reach the Editorial Department at editorial@circuitcellar.com, @circuitcellar, and facebook.com/circuitcellar

Buck Converter Has Unique Control Scheme

Texas Instruments has introduced a 16-V input, 40-A synchronous DC/DC buck converter with an internally compensated advanced-current-mode (ACM) control topology supporting frequency synchronization. TI’s TPS543C20 SWIFT converter provides enhanced efficiency by integrating its latest generation of low resistance high- and low-side MOSFETs into a thermally efficient small-footprint package. Designers can stack two converters side by side to drive loads up to 80 A for processors in space-constrained and power-dense applications in various markets, including wired and wireless communications, enterprise and cloud computing, and data storage systems.

DKFsSTcVAAAx4B4The unique internally compensated ACM control topology with fast transient response maintains stability over a wide range of input and output voltages. What makes ACM different is that it is an emulated peak-current-mode control topology that internally generates a ramp with the ability to dynamically adjust for stability over a wide range of operating switching frequencies. This provides the best of both traditional fixed frequency for low noise operation and constant on-time (COT) control for fast transient without external compensation.

TPS543C20 key features and benefits

  • Provides greater than 90 percent efficiency at a 40-A peak-load current.
  • Maintains 0.5 percent reference-voltage accuracy over temperature and full differential remote-voltage sensing to meet the voltage-accuracy requirements of deep submicron processors.
  • Provides up to 80 A at point-of-load when stacking two converters.
  • Offers very high power density and the PowerStack quad flat no-leads (QFN) package enables easy heat sinking from the single ground pad.

Available now from through the TI store and authorized distributors, the TPS543C20 is offered in a 40-pin, 5-mm-by-7-mm-by-1.5-mm PowerStack QFN package and is priced in small reels at US$5.24 for 1,000-unit quantities.

Texas Instruments | www.ti.com

Tools for Cypress Semi’s PSoC BLE 6 MCU

Cypress Semiconductor has announced the public release of the PSoC 6 BLE Pioneer Kit and PSoC Creator Integrated Design Environment (IDE) software version 4.2 that enable designers to begin development with the PSoC 6 microcontroller (MCU) for IoT applications. PSoC BLE 6 is the industry’s lowest power, most flexible MCU with built-in Bluetooth Low Energy wireless connectivity and integrated hardware-based security in a single device.

Early adopters are already using the flexible dual-core architecture of PSoC 6, using the ARM Cortex-M4 core as a host processor and the Cortex-M0+ core to manage peripheral functions such as capacitive sensing, Bluetooth Low Energy connectivity and sensor aggregation. Early adopter applications include wearables, personal medical devices and wireless speakers. Designers are also utilizing the built-in security features in PSoC 6 to help guard against unwanted access to data.

CY8CKIT-062-BLEThe PSoC BLE Pioneer Kit features a PSoC 63 MCU with Bluetooth Low Energy (BLE) connectivity. The kit enables development of modern touch and gesture-based interfaces that are robust and reliable with a linear slider, touch buttons and proximity sensors based on the latest generation of Cypress’ industry-leading CapSense capacitive-sensing technology. Designers can also use the board to add USB Power Delivery (PD) with its Cypress EZ-PD CCG3 USB-C controller. The kit also includes a 2.7-inch E-ink Display Shield add-on board (CY8CKIT-028-EPD) with thermistor, digital mic, and 9-axes motion sensor.

Offering best-in-class flexibility and ease-of-use, the PSoC 6 MCU architecture can serve as the catalyst for differentiated, visionary IoT devices. Designers can use software-defined peripherals to create custom analog front-ends (AFEs) or digital interfaces for innovative system components such as E-ink displays. The architecture is supported by Cypress’ PSoC Creator IDE and the expansive Arm ecosystem. Designers can find more information about PSoC Creator at http://www.cypressw.com/creator.

The PSoC 6 BLE Pioneer Kit (CY8CKIT-062-BLE) is available for purchase for $75 at the Cypress Online Store and through select distribution partners. PSoC 6 devices are currently sampling. Production devices are expected by the end of 2017.

Cypress Semiconductor | www.cypress.com

Antenna Measurement Made Easy

For web Lacoste Lead Image

Covering the Basics

If you’re doing any kind of wireless communications application, that probably means including an antenna in your design. The science of antennas is complex. But here Robert shows how the task of measuring an antenna’s performance is less costly and exotic than you’d think.

By Robert Lacoste

Now that wireless communications is ubiquitous, chances are you’ll be using Bluetooth, Wi-Fi, cellular, LoRa, MiWi or other flavor of wireless interface in your next design. And that means including an antenna. Unfortunately, antenna design is not an easy topic. Even very experienced designers sometimes have had to wrestle with unexpected bad performances by their antennas. Case in point: Google “iPhone 4 antenna problem” and you will get more than 3 million web pages! In a nutshell, Apple tried to integrate a clever antenna in that model that was threaded around the phone. They didn’t anticipate that some users would put their fingers exactly where the antenna was the most sensitive to detuning. Was it a design flaw? Or a mistake by the users? It was hotly debated, but this so-called “Antennagate” probably had significant impact on Apple’s sales for a while.

I already devoted an article to antenna design and impedance matching (“The Darker Side: Antenna Basics”, Circuit Cellar 211, February 2008). Whether you include a standard antenna or design your own, you will never be sure it is working properly until you measure its actual performance. Of course, you could simply evaluate how far the system is working. But how do you go farther if the range is not enough? How do you figure out if the problem is coming from the receiver, the transmitter, propagation conditions or the antenna itself? My personal experience has been that the antenna is very often the culprit. With that in mind, it really is mandatory to measure whether or not an antenna is behaving correctly. Take a seat. This month, I will explain how to easily measure the actual performance of an antenna. You will see that the process is quite easy and that it won’t even need costly or exotic equipment.


Let’s start with some basics on antennas. First, all passive antennas have the same performance whether transmitting or receiving. For this article, I’ll consider the antenna as transmitting because that’s easier to measure. Let’s consider an antenna that we inject with a given radio frequency power Pconducted into its connector. Where will this power go? First off, impedance matching should be checked. If the impedance of the antenna is not well matched to the impedance of the power generator, then a part of the power will be reflected back to the generator. This will happen in particular when the transmit frequency is not equal to the resonant frequency of the antenna. In such a case, a part of Pconducted will be lost.  That is known as mismatch losses: Pavailable= Pconducted – MismatchLosses. While that itself is a very interesting subject, I have already discussed impedance matching in detail in my February 2008 article. I also devoted another article to a closely linked topic: standing waves. Standing waves appear when there is a mismatch. The article is “The Darker Side: Let’s play with standing waves” (Circuit Cellar 271, February 2013).

For the purpose of discussion here, I will for now assume that there isn’t any mismatching—and therefore no mismatch loss. …

Read the full article in the October 327 issue of Circuit Cellar

We’ve made the October 2017 issue of Circuit Cellar available as a sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.
Don’t miss out on upcoming issues of Circuit Cellar. Subscribe today!

Wideband Mixer Has 3 mm x 2 mm Package

Analog Devices announced the LTC5552, a double balanced mixer that features best-in-class wideband matching from 3 GHz to 20 GHz. The mixer can be used as an up- or down-converter. The LTC5552 is especially useful in up-conversion applications with its Analog Devices LTC5552DC capable differential IF port that enables the LO to be close in frequency to the RF. Its low LO to RF leakage of less than –25dBm greatly eases the burden on the external filter. Additionally, the mixer delivers excellent linearity of 20.1dBm IIP3 at 14 GHz, and 18.3dBm at 17 GHz. The device integrates a broadband LO buffer, requiring only 0dBm drive and effectively eliminating an external high power LO amplifier circuit. Moreover, the LTC5552 integrates a wideband balun transformer in its RF port, allowing single-ended 50Ω matched operation over its specified frequency range. All these features result in minimum external components, simplified design and a very small solution size.

The LTC5552’s exceptionally wide bandwidth and performance is ideal for a broad range of applications, including 5G broadband wireless access, microwave backhaul, satellite broadband radios, radar systems, active antenna arrays, X, Ku and Ka band transceivers, RF test equipment, spectrum analysis and satellite communications. The LTC5552 is offered in a tiny 12-lead, 3mm x 2mm plastic QFN package. The device is rated from –40°C to 105°C case temperature to support extended environmental operating temperatures. The mixer is powered from a single 3.3 V supply and typically consumes 132 mA supply current. Additionally, the LTC5552 can be shut down via an enable pin. When deactivated, the device draws only 100 μA maximum standby current. The enable pin can also be driven directly to turn the device on and off rapidly in less than 0.2μs, supporting time-division duplex (TDD) or burst mode type transmitters and receivers. The LTC5552 is priced starting at $22.00 each in 1,000-piece quantities.

Analog Devices | www.analog.com

Mini PCIe Card Does Ethernet Over Fiber

Versalogic has announced the E4, a new Ethernet over fiber Mini PCIe expansion module for embedded computer systems. Ethernet over fiber offers an extremely dependable, highly secure Ethernet connection that operates over a much longer distance than copper. Where security matters, a fiber optic connection excels. Fiber optic cables have no electromagnetic signature, making them very difficult to tap compared to wired connections.

Veraslogic PR_MPEe-E4_HIVersalogic’s Ethernet over fiber card allows cable runs 5 times longer than Ethernet over copper. It protects against external electromagnetic interference and electrical surges. It also enables extreme security by removing the electro-magnetic signature from the connecting cables. The card supports full industrial temperature rating (-40° to +85°C) provides 1 Gbit/s speed with full duplex support.

The rugged E4 module provides a standardized way to add a bi-directional gigabit channel of Ethernet over fiber to an embedded computing solution. Using latching multi-mode LC type connectors, the E4 can transmit and receive data up to 550 m. The E4’s extremely small Mini PCIe format allows it to be added to an embedded computer board with very little impact to the overall size of the system. Compatible with a variety of popular x86 operating systems including Windows, Windows Embedded, and Linux, the E4 uses standard Ethernet software drivers.

Designed and tested for extended temperatures (-40° to +85°C), the E4 also meets MIL-STD-202G specifications to withstand high impact and vibration. The latching LC fiber optic connector provides additional protection within harsh environments. This new product is RoHS compliant, and includes VersaLogic’s 5+ year production life guarantee. The E4 is customizable, even in low OEM quantities. Customization options include conformal coating, revision locks, custom labeling, customized testing and screening. The VL-MPEe-E4E is available from stock at both Versalogic. and Digi-Key. Pricing is $275 in OEM quantities.

Versalogic | www.versalogic.com

2.5 A Step-Down Regulator Keeps EMC/EMI Emissions Low

Analog Devices, which recently acquired Linear Technology, has announced the LTM8065, a µModule (power module) step-down regulator with up to 40 V input voltage (42 V abs max), which can safely operate from unregulated or fluctuating 12 V to 36 V input supplies in noisy environments such as industrial robotics, test and measurement, medical, factory automation and avionics systems. The Silent Switcher architecture minimizes EMC/EMI emissions enabling the LTM8065 to pass CISPR 22 class B for use in noise-sensitive signal processing applications, including imaging and RF systems. The LTM8065’s small 6.25 mm x 6.25 mm x 2.32 mm BGA package includes a switching regulator controller, power switches, inductor and other supporting components. With only two 0805 sized capacitors and two 0603 sized resistors, the LTM8065’s solution occupies approximately 100mm², about half the size of equivalent power level module solutions.

LTM8065The LTM8065 can deliver 2.5 A of continuous (3.5 A peak) output current to a 5 V load from a 12 V input at up to 85°C ambient without a heat sink or airflow. The output voltage is adjustable with one resistor from 0.97 V to 18 V. This wide output voltage range provides versatility, using one product to generate common system bus voltage of 3.3 V, 5 V, 12 V and 15 V. The switching frequency is adjustable by an external single resistor or can be synchronized to an external clock from 200 kHz to 3 MHz. It enables customer operation of the device in or out of the specific frequency. The LTM8065 has four modes: Burst Mode® operation, pulse-skipping mode, pulse-skip mode with spread spectrum modulation and external synchronization mode. The quiescent current at burst mode is 8 µA, making it ideal for battery operating systems.

The LTM8065 operating temperature range is –40°C to 125°C. 1,000-piece pricing starts at $7.75 each.

Analog Devices – Linear Technology | www.linear.com

IP65-Rated E3800-Based Panel PCs Feature Fanless Design

Winsystems has released its advanced IP65-rated panel PC delivering high reliability and an extended operating temperature range in a thin, fanless design. The PPC65B series offers a rugged design for extreme environments and industrial IoT applications ranging from -20ºC to +70ºC. Winsystems’ latest industrial PCs accommodate panel and VESA mounting configurations. When mounted properly, the sealed front bezel can be washed down with a pressure hose, making this series ideal for industrial control applications such as food processing and fleet management. The PPC65B series provides a low-profile solution for Human Machine Interface (HMI) and display applications in harsh environments that might otherwise require extensive packaging to protect the embedded computer.

Winsystems ppc65b-1x_a-1000x979These IP65-rated panel PCs, which support Linux and Windows 10 operating systems, use the 1.9 GHz Quad-Core Intel Atom processor and include up to 8 GB of RAM. They deliver fast graphics at high resolutions—1024 X 768 and 1280 x 1024—accessed via a five-wire resistive touchscreen. The rugged design also incorporates a SATA controller with 2.5-inch HDD/SSD and wide input power: 12 VDC to 24 VDC.

Optimal connectivity and I/O for embedded systems is achieved through 2x GbE Ethernet ports, a 1x USB 2.0 port (accommodating up to 3x with expansion) and 1x USB 3.0 port. A watchdog timer is included. The PPC65B series also includes options for expansion with 2x RS-232/422/485 plus 2x USB (default).

Winsystems | www.winsystems.com

November Circuit Cellar: A Sneak Preview

The November issue of Circuit Cellar magazine is coming soon. Want a sneak peak? We’ve got a great section of excellent embedded electronics articles for you.

Not a Circuit Cellar subscriber?  Don’t be left out! Sign up today:

Here’s a sneak preview of November Circuit Cellar:


IoT Gateway Advances Take Diverse Paths: Flexible Networked Solutions
The Internet-of-Things (IoT) phenomenon offers huge opportunities. Circuit Cellar Chief Editor Jeff Child explores how IoT gateways play a vital role in those systems by providing Nov 328 coverbidirectional communication between the devices in the field and the cloud.

Power Analysis Attack on RSA: Asymmetric Adventures
Colin O’Flynn has done a number of great columns about cryptography—in particular symmetric cryptography. This time he’s tackling an asymmetric algorithm: a RSA implementation. Colin describes what’s unique about an RSA cryptosystem and takes us through a power analysis attack.


Analog Solutions Fuel Industrial System Needs: Connectivity, Control and IIoT
Whether it’s connecting with analog sensors or driving actuators, analog ICs play many critical roles in industrial applications. Here, Circuit Cellar Chief Editor Jeff Child examines the latest analog technologies and products serving the needs of today’s industrial systems.

Using Power Audio Amplifiers in Untypical Ways (Part 2): More Alternative Uses
In Part 1 Petre Petrov described many interesting ways to use power audio amplifiers (PAAs) as universal building blocks similar to the op amps and comparators. Here, he discusses several more things that can be built from PAAs including wave generators and transformer drivers.


Gas Monitoring and Sensing (Part 2): Putting the Sensor to Work
Columnist Jeff Bachiochi continues his exploration of gas monitoring and sensing. This time he discusses some of the inexpensive sensors available that can be applied to this application. Jeff then tackles the factors to consider when calibrating these sensors and how to use them effectively.

Logger Device Tracks Amp Hours (Part 2): Alternative Energy Sources
n this follow on to Part 1 of his story, William Wachsmann describes putting to use the amp-hour logger he built using a microcontroller and a clamp-on ammeter. This time he discusses modifying the amp-hour software so it can be used as an analog input logger to measure solar and wind power.

Negative Feedback in Electronics: A Look at the Opposite Side
Complementing his discussion last month on positive feedback, columnist George Novacek now takes a look at negative feedback. Just like positive feedback, negative feedback can significantly change or modify a circuit’s performance.

LF Quartz Resonator Tester: A Stimulating Discussion
Ed Nisley returns to the rich topic of low-frequency quartz resonators. This time he describes a tester built with an ordinary Arduino Nano and an assortment of inexpensive RF modules.


Simulating a Hammond Tonewheel Organ (Part 1) Mimicking a Mechanical Marvel
Hammond tonewheel organs were based upon additive sine-wave synthesis. Because of that, it’s possible to simulate the organ using a microcontroller program that feeds its output waveform to a DAC. Brian Millier takes on this project, making use of an ARM-based Teensy module to do the heavy lifting.

Machine Auto-Sorts Resistors: MCUs, Measurement and Motor Control
Typical electronics lab benches become littered with resistors from past projects. These three Cornell University graduates tackled this problem by building a resistor sorting system. It enables users to input multiple resistors, measure their resistance and sort them. The project integrates motor controllers, resistance measurement and a graphical user interface.

Don’t Miss Our Newsletter: IoT Technology Focus

Coming to your inbox tomorrow: Circuit Cellar’s IoT Technology Focus newsletter. Tomorrow’s newsletter content covers wha’s happening with Internet-of-Things (IoT) technology–from devices to gateway networks to cloud architectures. This newsletter tackles news and trends about the products and technologies needed to build IoT implementations and devices.

Bonus: We’ve added Drawings for Free Stuff to our weekly newsletters. Make sure you’ve subscribed to the newsletter so you can participate.

everyware_server_M2M_cloudAlready a Circuit Cellar Newsletter subscriber? Great!
You’ll get your IoT Technology Focus newsletter issue tomorrow.

Not a Circuit Cellar Newsletter subscriber?
Don’t be left out! Sign up now:

Our weekly Circuit Cellar Newsletter will switch its theme each week, so look for these in upcoming weeks:

Embedded Boards.(10/24) The focus here is on both standard and non-standard embedded computer boards that ease prototyping efforts and let you smoothly scale up to production volumes.

October has a 5th Tuesday (10/31) There’s an extra Newsletter this month: PCB Design

Analog & Power. (11/7) This newsletter content zeros in on the latest developments in analog and power technologies including DC-DC converters, AD-DC converters, power supplies, op amps, batteries and more.

Microcontroller Watch. (11/14) This newsletter keeps you up-to-date on latest microcontroller news. In this section, we examine the microcontrollers along with their associated tools and support products.

4W Board Mount Power Supplies Feature Wide Input Voltage

TDK has announced the KAS series AC-DC power supplies, rated at 2 W and 4 W.  Accepting a very wide 90 Vac to 305 Vac, 47 Hz – 440 Hz input, these board mounted converters will operate from 115 V, 230 V and 277 V nominal inputs.  Target applications include security systems, building automation, professional household appliances, portable equipment and products requiring a separate standby voltage.

kasThe series has a double insulated Class II construction, requiring no earth ground connection and has a 3,000 Vac primary to secondary isolation. Available output voltages are 3.3 V, 5 V, 8 V, 9 V, 12 V, 14 V, 15 V and 24 V and have a no-load power consumption of less than 300 mW. The KAS units are encapsulated in a plastic resin fiberglass case, providing additional protection against shock and vibration. The 2W KAS2 measures 28.5 x 25.8 x 17.0 mm and the 4W KAS4 37.0 x 27.5 x 17.5 mm.

The KAS2 will operate in ambient temperatures of -40 to +80°C, derating linearly to 40% load above 60°C. The KAS4 has a temperature range of up to -40 to +70°C, with model dependent derating.  All the power supplies are certified to IEC/EN/UL/CSA 60950-1 and are designed to meet IEC/EN 60335-1 with CE marking for the Low Voltage and RoHS2 Directives.  The series is compliant to EN 55032-B (radiated and conducted) and will meet EN 55024 immunity standards with an external varistor.

Main features and benefits

  • 90 – 305 VAC input voltage
  • Class II construction
  • Wide temperature range, up to -40 to +80°C
  • < 0.3 W off-load power consumption

TDK-Lambda | www.us.tdk-lambda.com

COM Express Type 7 Card Sports Atom C3000

Congatec has announced the launch of the conga-B7AC, a new Intel Atom C3000 processor based COM Express Type 7 Server-on-Module with 10 GbE support. With a power consumption starting at only 11 W, the board blends the 16-core Atom processor with a four a channel GbE real-time capable network. The feature set is designed for modular industrial micro servers as well as rugged telecom and network equipment, such as small cells, factory gateways and storage systems. It is deployable even in the extended temperature range from -40°C to +85°C.

The conga-B7AC is based on the new PICMG COM Express 3.0 specification. As a standardized building block, it is well suited for efficient custom designs of very small sized, passively cooled embedded edge systems. The new modules are application ready for redundant, real-time communication and virtualization platforms.

conga-B7AC_pressThey are designed to maximize uptime and resilience, minimize latency and to get the most out of each processing core. Their cloud API for distributed embedded edge servers further provides all the capabilities that data center managers need to remotely monitor system health, power consumption and environmental conditions. With the support of up to 20 PCIe lanes, the new Intel Atom C3000 processor based COM Express Type 7 Server-on-Modules also offer minimum latency for storage devices as well as very fast access lanes to all the various sensor networks, field buses and industrial Ethernet links.

The new conga-B7AC COM Express Type 7 Server-on-Modules are available with 8 different Intel Atom server processors, from the 16-core Intel Atom C3958 processor to the quad-core C3508 for the extended temperature range (-40°C to +85°C). All modules provide up to 48 GB of fast 2400 DDR4 memory with or without error correction code (ECC) depending on customers’ requirements. They offer very high network capabilities with up to 4x 10 GbE and the Network Controller Sideband Interface (NC-SI) for connecting a baseboard management controller (BMC) allowing out-of-band remote manageability. Flexible system extensions including NVMe flash storage can be connected via up to 12x PCIe Gen 3.0 lanes and 8x PCIe Gen 2.0 lanes. 2x SATA 6G ports are available for conventional storage media. Further I/O interfaces include 2x USB 3.0, 4x USB 2.0, LPC, SPI, I2C Bus and 2x UART. Additionally, the module hosts a trusted platform module (TPM) for security sensitive network appliances.

Congatec | www.congatec.com

FREE Sample Issue – Oct. 2017


We’ve made the October 2017 issue of Circuit Cellar available as a sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.

Don’t miss out on upcoming issues of Circuit Cellar. Subscribe today!

Inside This Issue:
Emulating Legacy Interfaces
Do it with Microcontrollers
By Wolfgang Matthes

Building a Retro TV Remote
PIC MCU-Based Design
By Dev Gualtieri
Building a Robot Hand
With Servos and Electromyography
By Michael Haidar, Jason Hwang and Srikrishnaa VadivelLogger Device Tracks Amp Hours (Part 1)
Measuring Home Electricity
By William Wachsmann

Commercial Drone Design Solutions Take Flight

Chips, Boards and Platforms
By Jeff Child

Design for Manufacturing: Does It Have to be so Difficult?
An interview with Scott N. Miller and Thos Niles
By Wisse Hettinga

Signal Chain Tech Pushes Bandwidth Barriers
ADCs, FPGAs and DACs
By Jeff Child

Embedded in Thin Slices
Build an Embedded Systems Consulting Company (Part 6)
Trade-Offs of Fixed-Price Contracts
By Bob JapengaThe Consummate Engineer
In the Loop on Positive Feedback
New Value in an Old Concept
By George Novacek


The Darker Side
Antenna Performance Measurement Made Easy
Covering the Basics
By Robert Lacoste
From the Bench
Gas Monitoring and Sensing (Part 1)
Fun with Fragrant Analysis
By Jeff BachiochiTECH THE FUTURE
The Future of PCB Design

Racing to Keep Pace With PCB Complexities
By Duane Benson

Don’t miss out on upcoming issues of Circuit Cellar. Subscribe today!

Logger Device Tracks Amp Hours (Part 1)

Measuring Home Electricity

Setting out to monitor and log electricity usage in his house, Bill built an amp-hour
logger using a microcontroller and a clamp-on ammeter. He gets into the software
development details exploring solutions like mbed and Microsoft Visual Studio.

By William Wachsmann

Like many people I found that electricity costs have been increasing rapidly over the past few years. Where I live, we have smart meters that allow the power company to charge different rates for high usage, moderate usage and low usage times of the day. The bills show how much energy is used during the different periods but only for the dwelling as a whole.

For this project, I used an NXP-Freescale FRDM-KL25Z microcontroller board.

For this project, I used an NXP-Freescale FRDM-KL25Z microcontroller board.

I wanted to know which parts of my house use how much electricity and at what times of the day. With this information, I would be able to see what parts of the house are using how much energy, and I’d even be able to calculate how much it’s costing to run certain appliances. I could then look into the feasibility of supplementing my energy supply with solar or wind, or maybe use a battery storage system that is charged in the less expensive hours for use during peak periods. Or perhaps even some combination of all three.


To measure AC current, you normally use a “Clamp on Ammeter” on either the live or neutral wire in the circuit of interest. These ammeters are readily available but they will only tell you the current at the particular point in time that you are using it. What I needed was one that I could leave connected over a 24-hour period and get a log of the current usage throughout the day and night. If such a device exists, I was unable to find one, so I needed to make my own.

The device would have to monitor currents in 120 V and 240 V AC circuits and be reasonably accurate over a range of 200 mA to 30 A. The price we pay for electricity is based on kilowatt-hours (kW-h) multiplied by the rate— usually specified in cents-per-kWh. In my case, in the fall of 2016 we were paying an average of about $ 0.27 / kWh after all extra charges such as delivery and taxes were included.

Using the data from the amp-hour logger would allow calculation of the number of kWh used in each circuit of my house. Since kWh is a measure of energy I also needed to know what the voltage is at the time that the current is being measured. Then, given that P = VI, I would get a measure of the power being used at a given time. Integrating this over a period of time gives me the energy in watt-hours or—dividing by 1,000—in kWh.

To be really accurate, I should measure the voltage as well as the current but I have found that whenever I check the voltage it is pretty constant at 120 V (+ or – a couple of volts). Therefore, using a nominal value of 120 V (or 240 V for some circuits) should be accurate enough for my purposes. If the amp-hour logger is designed to save current measurements for each minute, that should give a pretty good indication of load changes in the circuit that is being monitored. Also, just adding up the amp-hour/minute readings effectively integrates them and provides the total amp-hours used over a 24-hour period. Multiply this by the voltage and divide by 1,000 and I’ll get the number of kWh used in a day. Great. That’s the theory. Now to make something that will work.

Read the full article in the October 327 issue of Circuit Cellar

We’ve made the October 2017 issue of Circuit Cellar available as a sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.
Don’t miss out on upcoming issues of Circuit Cellar. Subscribe today!

Murata Expands Switching Regulator DC/DC Converter Family

Murata has added a 12 V model to its OKI-78SR series of non-isolated switching regulator DC/DC power converters for embedded applications. The fixed single output converter offers both tight regulation and high efficiency directly at the power usage site, and is a direct plug-in replacement for TO-220 package 78xx series linear regulators.

oki-78sr-12-prRated at 12V/1A, when powered from a 24V source, the OKI-78SR-12/1.0-W36-C converter’s efficiency is a very high 95%, eliminating the need for a heatsink that adds cost and increases complexity in the design and manufacturing processes. Cleverly packaged in the form of a three-terminal 78xx linear regulator, the converter operates from a source voltage of 15 to 36V and is available in both vertical and horizontal mounting options. The package size is just 10.4 x 7.62 x 16.5mm (0.41 x 0.3 x 0.65 inches).

Murata’s OKI-78SR series is suitable in a wide range of applications, including computing, networking, telecommunications, industrial, aerospace and rail. Indeed, it is ideal for any application where the ambient temperature ranges from -40 to 85°C, which has a source/system voltage in the range of 15 to 36 Vdc, and where the output requirement is for 12 V at 1 A. Standard features include a factory-set Vout at 12 Vdc, short-circuit/over-current protection, UL/EJ/IEC 60950-1, second edition safety approvals and RoHS compliance.

The OKI-78SR series incorporates advanced assembly techniques and the latest fixed switching frequency technology for power conversion available today. The optional packaging configurations, safety features, high reliability, state-of-the-art figures for efficiency, thermal management, dynamic load response, industry standard package and OCP protection features offer an unmatched level of performance.

Murata Power Solutions | www.murata-ps.com

Arduino Board Pair Boasts LoRa and GSM Capabilities

Arduino has introduced a pair of new Internet-of-Things (IoT)  boards with embedded LoRa and GSM capabilities. The boards were first unveiled at World Maker Faire New York. The Arduino MKR WAN 1300 and MKR GSM 1400 enable system developers to quickly add connectivity to their projects and ease the development of battery-powered IoT edge applications. Both of the highly compact boards measure just 67.64 mm x 25 mm, together with low power consumption, making them an ideal choice for emerging battery-powered IoT edge devices in the MKR form factor. Suitable applications examples include environmental monitoring, tracking, agriculture, energy monitoring and home automation.

Arduino DKb9irAW4AAM320-1Offering 32-bit computational power similar to the Arduino MKR ZERO board, the MKR WAN 1300 is based around the Murata LoRa low-power connectivity module and the Microchip SAM D21 microcontroller, which integrates an ARM Cortex-M0+ processor, 256 KB Flash memory and 3 2KB SRAM. The board’s design includes the ability to be powered by either two 1.5 V AA or AAA batteries or an external 5 V input via the USB interface—with automatic switching between the two power sources.

In addition, the MKR WAN 1300 offers the usual rich set of I/O interfaces expected with an Arduino board, and ease of use via the Arduino IDE software environment for code development and programming. Other features  include an operating voltage of 3.3 V; eight digital I/Os; 12 PWM outputs; and UART, SPI and I2C interfaces.

Like the MKR WAN 1300, the Arduino MKR GSM 1400 is based on the SAM D21, but integrates a u-blox module for global 3G communications. The board features automatic power switching, however, it uses either a 3.7 V LiPo battery or an external Vin power source delivering 5 V to 12 V. While the USB port can also be used to supply 5 V to the board, the MKR GSM 1400 is able to run with or without the battery connected.

The MKR GSM 1400 provides a rich set of I/O interfaces including: eight digital I/Os; 12 PWM outputs; UART, SPI and I2C interfaces; analog I/O including seven inputs and one output; and eight external interrupt pins. Both boards are now available for pre-order on the Arduino Store.

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