IoT Modules Enable Large-Scale LTE-M and NB-IoT Deployments

Telit has announced the ME310G1 (shown) and ME910G1 modules, designed for mass-scale LTE-M and NB-IoT deployments that feature hundreds of thousands or millions of devices. Based on the new Qualcomm 9205 LTE modem and featuring optional 2G fallback, the modules also provide a future-proof foundation for IoT deployments that span legacy networks, 4G and 5G.
The ME310G1 and ME910G1 are the first 3GPP Release 14 additions to the Telit portfolio and the first members of Telit’s new series based on the Qualcomm 9205 LTE IoT Modem, which was announced in late 2018. The highly compact chipset enables Telit to meet booming global demand for ultra-small modules for applications such as wearable medical devices, fitness trackers and industrial sensors.

The new modules are ideal for battery-powered applications via improved features such as Power Saving Mode (PSM) and extended Discontinuous Reception (eDRX), which periodically wakes up the device to transmit only the smallest amounts of data necessary before returning to sleep mode. Both modules also ensure reliable indoor connections, with a maximum coupling loss of up to +15dB/+20dB for superior in-building penetration compared to earlier LTE standards.

The multi-band ME310G1 and ME910G1 are available in versions with 2G fallback for use in areas where LTE-M/NB-IoT service is yet to be deployed. These versions also support GSM voice and will support VoLTE for applications that require the ability to make phone calls.

The ME910G1 is the latest member of Telit’s best-selling xE910 and family. The ME910G1 is also a drop-in replacement in existing devices based on the family’s modules for 2G, 3G and the various categories of LTE. With Telit’s design-once-use-anywhere philosophy, developers can cut costs and development time by simply designing for the xE910 LGA common form factor, giving them the freedom to deploy technologies best suited for the application’s environment.

The ME310G1 LTE-only variant is less than 200 mm-squared and variant with 2G fallback is less than 300 mm2-squared and they enable enterprises to deploy new small footprint designs across many application areas including asset tracking, health-care monitoring, smart metering, portable devices, industrial sensors, home automation, and others that benefit from low-power and low-data rate capabilities. The xE310 family’s flexible perimeter footprint includes pin-to-pin compatible 2G and 4G modules, enabling integrators to design a single PCB layout and deploy a combination of technologies.

ME310G1 and ME910G1 samples are now available. Mass production begins in late 2019 and Q1 2020, depending on the product version.

Telit | www.telit.com

400 W 1/8th Brick DC-DC Converters Support PMBus

Murata has announced the introduction of its DSE Series, a fully isolated, 12 Vout, 400 W eighth brick DC-DC converter with a DOSA compliant digital interface to support the PMBus standard for communication and control. The Series, which also includes DAE and DCE products, has a droop load sharing option for paralleling up to three modules in some of the most power demanding applications. Further, the series meets the international TNV standard for Input Voltage with a 36-75 Vin range and provides 2250 VDC isolation for use in Power over Ethernet (PoE) applications.

The DSE series offers advanced power conversion technology, including a 32-bit Arm processor that controls critical conversion functions and delivers a digital interface for use in the end system application. The PMBus digital interface can be used to customize the modules’ configuration for specific functions and presents system engineers with critical telemetry information.

Multiple pin configurations are available, as the DSE provides a DOSA standard digital eighth brick pinout with sense, trim, and PMBus. The DAE provides a DOSA analog eighth brick pinout with sense and trim (no PMBus). The DCE is a DOSA analog eighth brick in the traditional 5-pin package. Target applications include telecommunications, networking, wireless, pre-amplifiers, industrial and test equipment.

Murata Power Solutions | www.murata-ps.com

 

mmWave Chipset Solution Eases 5G System Design

Analog Devices has introduced a new solution for millimeter wave (mmWave) 5G featuring high-integrations for next gen cellular network infrastructure. The solution combines ADI’s advanced beamformer IC, up/down frequency conversion (UDC) and additional mixed signal circuitry. ADI is calling this an optimized “Beams to Bits” signal chain.

The new mmWave 5G chipset includes the 16-channel ADMV4821 dual/single polarization beamformer IC, 16-channel ADMV4801 (shown) single-polarization beamformer IC and the ADMV1017 mmWave UDC. The 24- to 30-GHz beamforming + UDC solution forms a 3GPP 5G NR compliant mmWave front-end to address the n261, n257 and n258 bands.

The high channel density, coupled with the ability to support both single- and dual-polarization deployments, greatly increases system flexibility and reconfigurability for multiple 5G use cases while best-in-class equivalent isotropically radiated power (EIRP) extends radio range and density. According to ADI, the company’s experience in mmWave enables system designers to take advantage of world class applications and system design to optimize complete lineups for thermal, RF, power and routing considerations.

Analog Devices | www.analog.com

 

Semtech LoRa Tech Leveraged for Construction and Mining Gear

Semtech has announced that MachineMax, a provider of smart solutions for fleet management, construction and mining applications, has integrated Semtech’s LoRa devices and wireless radio frequency technology (LoRa Technology) into a new smart construction machine usage tracking solution. With Semtech’s LoRa Technology, MachineMax says they were able to create simple, easy to deploy solutions which effectively monitor machine status from anywhere on a construction or mining site.

Machine idling, where a machine’s engine is running but the machine is not actively in use, accounts for an estimated 37% of the time a construction or mining machine is operating on average. Idling results in an increased amount of fuel waste and machine wear, without creating productive machine output. Previously, monitoring the usage status of a mining or construction fleet was accomplished manually, with site managers continually checking on the use status of machines, an expensive and time consuming task.

MachineMax developed a LoRa-based solution which can be easily deployed onto fleet machines in under a minute. The devices attach magnetically and gather real-time data on machine usage status, such as whether or not a machine is idle. With real-time data on when a machine is in use, site managers can make more efficient use of a machine’s time to prevent idling, reducing the amount of fuel used and prolonging machine life.

Semtech’s LoRa devices and wireless radio frequency technology is a widely adopted long-range, low-power solution for IoT that gives telecom companies, IoT application makers and system integrators the feature set necessary to deploy low-cost, interoperable IoT networks, gateways, sensors, module products and IoT services worldwide. IoT networks based on the LoRaWAN specification have been deployed in 100 countries and Semtech is a founding member of the LoRa Alliance.

Semtech | www.semtech.com

 

IoT Smart Water Care System Leverages Nordic’s BLE SoC

Nordic Semiconductor has announced that ConnectedYard has selected Nordic’s nRF51822 Bluetooth Low Energy (BLE) SoC to provide the wireless connectivity for pHin, a smart water care solution designed to simplify the care and maintenance of backyard swimming pools and hot tubs. pHin combines an nRF51822 SoC- and Wi-Fi-enabled smart monitor and smartphone app that monitors water chemistry and temperature around the clock and notifies customers when they need to take action.
The pHin Smart Monitor floats in the pool or hot tub and continuously monitors water temperature and water chemistry—including pH and oxidation reduction potential (ORP)—and then wirelessly sends the water chemistry data over the Nordic SoC-enabled Bluetooth LE connection to the pool owner’s Bluetooth 4.0 (or later) smartphone and the ‘pHin WiFi bridge’. The data is also available via the pHin Partner Portal, which allows retailers, service technicians, and pool builders to remotely monitor water conditions and provides features that help drive consumers back to their local retailer for chemicals and other products. pHin uses a coin cell battery to achieve over two years of battery life between replacement, thanks in part to the ultra low power consumption of the nRF51822 SoC.

Nordic’s nRF51822 is ideally suited for Bluetooth LE and 2.4GHz ultra low power wireless applications. The nRF51822 is built around a 32-bit Arm® Cortex M0 CPU, 2.4GHz multiprotocol radio, and 256kB/128kB Flash and 32kB/16kB RAM. The SoC is supplied with Nordic’s S130 SoftDevice, a Bluetooth 4.2 qualified concurrent multi-link protocol stack. Nordic’s software architecture includes a clear separation between the RF protocol software and the application code, simplifying development for ConnectedYard’s engineers and ensuring the SoftDevice doesn’t become corrupted when developing, compiling, testing and verifying application code.

Nordic Semiconductor | www.nordicsemi.com

IoT Monitoring System for Commercial Fridges

Using LoRa Technology

IoT implementations can take many shapes and forms. Learn how these four Camosun College students developed a system to monitor all the refrigeration units in a commercial kitchen simultaneously. The system uses Microchip PIC MCU-based monitoring units and wireless communication leveraging the LoRa wireless protocol.

By Tyler Canton, Akio Yasu, Trevor Ford and Luke Vinden

In 2017, the commercial food service industry created an estimated 14.6 million wet tons of food in the United States [1]. The second leading cause of food waste in commercial food service, next to overproduction, is product loss due to defects in product quality and/or equipment failure [2].

While one of our team members was working as the chef of a hotel in Vancouver, more than once he’d arrive at work to find that the hotel’s refrigeration equipment had failed overnight or over the weekend, and that thousands of dollars of food had become unusable due to being stored at unsafe temperatures. He always saw this as an unnecessary loss—especially because the establishment had multiple refrigeration units and ample space to move product around. In this IoT age, this is clearly a preventable problem.

For our Electronics & Computer Engineering Technologist Capstone project, we set forth to design a commercial refrigeration monitoring system that would concurrently monitor all the units in an establishment, and alert the chefs or managers when their product was not being stored safely. This system would also allow the chef to check in on his/her product at any time for peace of mind (Figure 1).

Figure 1
This was the first picture we took of our finished project assembled. This SLA printed enclosure houses our 10.1″ LCD screen, a Raspberry Pi Model 3B and custom designed PCB.

We began with some simple range testing using RFM95W LoRa modules from RF Solutions, to see if we could reliably transmit data from inside a steel box (a refrigerator), up several flights of stairs, through concrete walls, with electrical noise and the most disruptive interference: hollering chefs. It is common for commercial kitchens to feel like a cellular blackout zone, so reliable communication would be essential to our system’s success.

System Overview

We designed our main unit to be powered and controlled by a Raspberry Pi 3B (RPi) board. The RPi communicates with an RFM95W LoRa transceiver using Serial Peripheral Interface (SPI). This unit receives temperature data from our satellite units, and displays the temperatures on a 10.1″ LCD screen from Waveshare. A block diagram of the system is shown in Figure 2. We decided to go with Node-RED flow-based programming tool to design our GUI. This main unit is also responsible for logging the data online to a Google Form. We also used Node-RED’s “email” nodes to alert the users when their product is stored at unsafe temperatures. In the future, we plan to design an app that can notify the user via push notifications. This is not the ideal system for the type of user that at any time has 1,000+ emails in their inbox, but for our target user who won’t allow more than 3 or 4 to pile up it has worked fine.

Figure 2
The main unit can receive temperature data from as many satellite units as required. Data are stored locally on the Raspberry Pi 3B, displayed using a GUI designed by Node-RED and logged online via Google Sheets.

We designed an individual prototype (Figure 3) for each satellite monitoring unit, to measure the equipment’s temperature and periodically transmit the data to a centralized main unit through LoRa communication. The units were intended to operate at least a year on a single battery charge. These satellites, controlled by a Microchip Technology PIC24FJ64GA704 microcontroller (MCU), were designed with an internal Maxim Integrated DS18B20 digital sensor (TO-92 package) and an optional external Maxim

Figure 3
This enclosure houses the electronics responsible for monitoring the temperatures and transmitting to the main unit. These were 3D printed on Ultimaker 3 printers.

Integrated DS18B20 (waterproof stainless steel tube package) to measure the temperature using the serial 1-Wire interface.

Hardware

All our boards were designed using Altium Designer 2017 and manufactured by JLCPCB. We highly recommend JLCPCB for PCB manufacturing. On a Tuesday we submitted our order to the website, and the finished PCB’s were manufactured, shipped, and delivered within a week. We were amazed by the turnaround time and the quality of the boards we received for the price ($2 USD / 10 PCB).

Figure 4
The main unit PCB’s role is simply to allow the devices to communicate with each other. This includes the RFM95W LoRa transceivers, RPi, LCD screen and a small fan

Main Unit Hardware: As shown in Figure 4, our main board’s purpose is communicating with the RPi and the LCD. We first had to select an LCD display for the main unit. This was an important decision, as it was the primary human interface device (HID) between the system and its user. We wanted a display that was around 10″—a good compromise between physical size and readability. Shortly after beginning our search, we learned that displays between 7″ and 19″ are not only significantly more difficult to come by, but also significantly more expensive. Thankfully, we managed to source a 10.1″ display that met our budget from robotshop.com. On the back of the display was a set of female header pins designed to interface with the first 26 pins of the RPi’s GPIO pins. The only problem with the display was that we needed access to those same GPIO pins to interface with the rest of our peripherals.

Figure 5
Our main board, labeled Mr. Therm, was designed to attach directly to the LCD screen headers. RPi pins 1-26 share the same connectivity as the main board and the LCD.

We initially planned on fixing this problem by placing our circuit board between the RPi and the display, creating a three-board-stack. Upon delivery and initial inspection of the display, however, we noticed an undocumented footprint that was connected to all the same nets directly beneath the female headers. We quickly decided to abandon the idea of the three-board-stack and decided instead to connect our main board to that unused footprint in the same way the RPi connects to display (Figure 5). This enabled us to interface all three boards, while maintaining a relatively thin profile. The main board connects four separate components to the rest of the circuit. It connects the RFM95W transceiver to the RPi, front panel buttons, power supply and a small fan.

Read the full article in the April 345 issue of Circuit Cellar
(Full article word count: 3378 words; Figure count: 11 Figures.)

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

Note: We’ve made the October 2017 issue of Circuit Cellar available as a free 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.

BLE Multicore MCUs Embed Arm Cortex M33 CPU

Dialog Semiconductor has announced its SmartBond DA1469x family of Bluetooth low energy SoCs, a range of multi-core MCUs for wireless connectivity. The devices’ three integrated cores have each been carefully chosen for their capabilities to sense, process and communicate between connected devices, says Dialog. To provide the devices’ processing power, the DA1469x product family is the first wireless MCU in production with a dedicated application processor based on the Arm Cortex-M33 CPU, according to Dialog.

The M33 is aimed at compute intensive applications, such as high-end fitness trackers, advanced smart home devices and virtual reality game controllers. The DA1469x devices have a new integrated radio that offers double the range compared to its predecessor together with an Arm Cortex-M0+ based software-programmable packet engine that implements protocols and provides full flexibility for wireless communication.

On the connectivity front, an emerging application is for manufacturers to deploy accurate positioning through the Angle of Arrival and Angle of Departure features of the newly introduced Bluetooth 5.1 standard. With its world-class radio front end performance and configurable protocol engine, the DA1469x complies with this new version of the standard and opens new opportunities for devices that require accurate indoor positioning such as building access and remote keyless entry systems.

To enhance the sensing functionality of the DA1469x, the M33 application processor and M0+ protocol engine is complemented with a Sensor Node Controller (SNC), which is based on a programmable micro-DSP that runs autonomously and independently processes data from the sensors connected to its digital and analog interfaces, waking the application processor only when needed. In addition to this power-saving feature, a state-of-the-art Power Management Unit (PMU) provides best-in-class power management by controlling the different processing cores and only activating them as needed.

The SoCs feature up to 144 DMIPS, 512 KB of RAM, memory protection, a floating-point unit, a dedicated crypto engine to enable end-to-end security and expandable memories, ensuring a wide range of advanced smart device applications can be implemented using the chipset family and supporting a range of key value-add interfaces to extend functionality even further.

The PMU also provides three regulated power rails and one LDO output to supply external system components, removing the requirement of a separate power management IC (PMIC). Additionally, the DA169x product family come equipped with a range of key value-add interfaces including a display driver, an audio interface, USB, a high-accuracy ADC, a haptic driver capable of driving both ERM and LRA motors as well as a programmable stepping motor controller.

Developers working with the DA1469x product family can make use of Dialog’s software development suite – SmartSnippets – which gives them the tools they need to develop best-in-class applications on the new MCUs. The DA1469x variants will start volume production in the first half of 2019. Samples and development kits are available now.

Dialog Semiconductor | www.dialog-semiconductor.com

 

RPi-Based IoT gateway Offers Cellular, Zigbee, Z-Wave or LoRa

By Eric Brown

Newark Element14 and Avnet have announced a Raspberry Pi based “SmartEdge Industrial IoT Gateway” with 2x Ethernet, Wi-Fi/BT, CAN, serial and optional Zigbee, Z-Wave or LoRa.

Avnet, which last year launched the Zynq UltraScale+ based ‘Ultra96 96Boards CE SBC, announced plans for the Avnet SmartEdge Industrial IoT Gateway at the CES show in early January. At Embedded World last month, Premier Farnell revealed more details on the Raspberry Pi based IoT gateway, which will launch this summer at Newark Element14 in North America and Farnell Element14 in Europe.


Avnet SmartEdge Industrial IoT Gateway 
(click image to enlarge)
The Avnet SmartEdge Industrial IoT Gateway will support Avnet’s IoT Connectplatform to enable cloud connectivity to Microsoft Azure. The Linux-driven embedded PC will support industrial automation applications such as remote monitoring, predictive maintenance, process control, and automation.

Premier Farnell did not say which Raspberry Pi is under the hood, but based on the WiFi support, it would appear to be the RPi 3 Model B rather than the B+. The limited specs announced for the gateway include 8GB eMMC, an HDMI port, and TPM 2.0 security. The image suggests there are also at least 2x USB ports and a coincell battery holder for a real-time clock.

For communications, you get dual 10/100 Ethernet ports as well as 2.4GHz WiFi and BLE 4.2 with an integrated antenna and external mount. The gateway also provides a mini-PCIe interface for optional cellular modems. In addition, the enclosure “features space for an additional internal accessory to provide Zigbee, Z-Wave, or LoRa capabilities, for example, or for multiple accessories through case expansion,” say Premier Farnell.

The system is further equipped with CAN-BUS and RS-232/485 interfaces with Modbus and DeviceNet support, as well as isolated digital I/O. There’s also a 40-pin expansion header for Raspberry Pi HATs and other add-on boards. The system has a wide-range 12-24V DC input plus DIN rail and wall mounting.

Further information

The Avnet SmartEdge Industrial IoT Gateway will launch this summer at Newark Element14 in North America and Farnell Element14 in Europe, with pricing undisclosed. More information is available in the Premier Farnell announcement and more may eventually appear on the Avnet website.

This article originally appeared on LinuxGizmos.com on March 4..

Avnet | www.avnet.com

Farnell Element14 | www.element14.com

Newark Element14 | www.newark.com

i.MX6-Based SBC Offers Global Cellular Expansion

VersaLogic has announced the Swordtail SBC that features models with either the NXP i.MX6 Quad (quad core), or the i.MX6 DualLite (dual core) processors. The SBC includes on-board Wi-Fi, Bluetooth and a cellular plug-in socket. At home in hostile environments the compact 95 mm x 95 mm computer board is rated for operation at full industrial temperature range (-40° to +85°C). Unlike many Arm-based “modules”, VersaLogic’s new Arm-based products are complete board-level computers. They do not require additional carrier cards, companion boards, connector break-out boards, or other add-ons to function.

Swordtail boards have been designed to enable transmission of maintenance or diagnostic information without the need for a wired connection. Wi-Fi and Bluetooth radios are included on board, and a NimbleLink Skywire socket supports a wide range of optional cellular and other wireless plug-ins. The Swordtail embedded computer board is suited for deployment into demanding industrial, smart city and transportation applications requiring rugged, long-life, power efficient and industrial temperature rated solutions.

Both Swordtail models feature soldered-on memory, and a variety of I/O connections. In addition to wireless capability, the on-board I/O includes a Gbit Ethernet port with network boot capability, two USB 2.0 Ports, serial I/O (RS-232), CAN Bus, microSD socket, and I2C interface. The boards can accommodate up to 32 GB of on-board flash storage.

Designed for COTS and MCOTS users, Swordtail can be modified for specific applications in quantities as low as 100 pieces. Many applications that require lower power or lower heat dissipation also need very high levels of reliability. Designed and tested for industrial temperature (-40° to +85°C) operation, VersaLogic’s Swordtail also meets MIL-STD-202H specifications to withstand high impact and vibration. Carefully engineered and validated, Swordtail excels in unforgiving environments.

Like other VersaLogic products, the Swordtail is designed for long-term availability (10+ year typical production lifecycle). The Swordtail single board computers (EPC-2702), will be available Q2 2019 from both VersaLogic and Digi-Key. OEM pricing starts at $236.

VersaLogic | www.versalogic.com

Guitar Video Game Uses PIC32

Realism Revamp

While music-playing video games are fun, their user interfaces tend to leave a lot to be desired. Learn how these two Cornell students designed and built a musical video game that’s interfaced using a custom-built wireless guitar controller. The game is run on a Microchip PIC32 MCU and has a TFT LCD display to show notes that move across the screen toward a strum region.

By Jake Podell and Jonah Wexler

While many popular video games involve playing a musical instrument, the controllers used by the player are not the greatest. These controllers are often made of cheap plastic, and poorly reflect the feeling of playing the real instrument. We have created a fun and competitive musical video game, which is interfaced with using a custom-built wireless guitar controller (Figure 1 and Figure 2). The motivation for the project was to experiment with video game interfaces that simulate the real-world objects that inspired them.

Figure 1
Front of the guitar controller. Note the strings and plectrum.

Figure 2
Back of the guitar controller

The video game is run on a Microchip PIC32 microcontroller [1]. We use a thin-film-transistor LCD display (TFT) to display notes that move across the screen toward a strum region. The user plays notes on a wireless mock guitar, which is built with carbon-impregnated elastic as strings and a conducting plectrum for the guitar pick. The game program running on the PIC32 produces guitar plucks and undertones of the song, while keeping track of the user’s score. The guitar is connected to an Arduino Uno and Bluetooth control center, which communicates wirelessly to the PIC32.

The controller was designed to simulate the natural motion of playing a guitar as closely as possible. We broke down that motion on a real guitar into two parts. First, users select the sound they want to play by holding the appropriate strings down. Second, the users play the sound by strumming the strings. To have a controller that resembled a real guitar, we wanted to abide by those two intuitive motions.

Fret & Strum Circuits

At the top of the guitar controller is the fret board. This is where the users can select the sounds they want to play. Throughout the system, the sound is represented as a nibble (4 bits), so we use 4 strings to select the sound.

Each string works as an active-low push-button. The strings are made of carbon-impregnated elastic, which feels and moves like elastic but is also conductive. Each string was wrapped in 30-gauge copper wire, to ensure solid contact with any conductive surfaces. The strings are each connected to screws that run through the fret board and connect the strings to the fret circuit (Figure 3).

Figure 3
Complete controller circuit schematic (on guitar).

The purpose of the fret circuit is to detect changes in voltage across four lines. Each line is branched off a power rail and connected across a string to an input pin on an Arduino Uno. Current runs from the power rail across each string to its respective input pin, which reads a HIGH signal. To detect a push on the string, we grounded the surface into which the string is pushed. By wrapping the fret board in a grounded conductive pad and pushing the string into the fret board, we are able to ground our signal before it can reach the input pin. When this occurs, the associated pin reads a LOW signal, which is interpreted as a press of the string by our system.

Along with the fret circuit, we needed a way to detect strums. The strum circuit is similar in its use of a copper-wrapped, carbon-impregnated elastic string. The string is connected through the fret board to an input pin on the Arduino, but is not powered. Without any external contact, the pin reads LOW. When voltage is applied to the string, the pin reads HIGH, detecting the strum. To mimic the strumming motion most accurately, we used a guitar pick to apply the voltage to the string. The pick is wrapped in a conductive material (aluminum foil), which is connected to the power rail. Contact of the pick applies voltage to the string, which on a rising edge denotes a strum.

Figure 4
Shown here is a block diagram of the controller signals.

As shown in Figure 4, the direct user interface for the player is the guitar controller. The physical interaction with the guitar is converted to an encoded signal by an Arduino mounted to the back of the guitar. The Arduino Uno polls for a signal that denotes a strum, and then reads the strum pattern across the four strings. The signal is sent over USB serial to a Bluetooth control station, which uses a Python script to broadcast the signal to an Adafruit Bluetooth LE module. The laptop that we used as a Bluetooth control station established a link between the controller and the Bluetooth receiver, and was paramount to the debugging and testing of our system. Finally, the Bluetooth module communicated over UART with the PIC, which interpreted the user’s signal in the context of the game [2].  …

Read the full article in the March 344 issue of Circuit Cellar
(Full article word count: 3271 words; Figure count: 10 Figures.)

Watch the project video here:

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

Note: We’ve made the October 2017 issue of Circuit Cellar available as a free 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.

Open-Spec, i.MX6 UL-Based SBC Boasts DAQ and Wireless Features

By Eric Brown

Technologic Systems has announced an engineering sampling program for a wireless- and data acquisition focused SBC with open specifications that runs Debian Linux on NXP’s low-power i.MX6 UL SoC. The -40°C to 85°C tolerant TS-7180 is designed for industrial applications such as industrial control automation and remote monitoring management, including unmanned control room, industrial automation, automatic asset management and asset tracking.


 
TS-7180, front and back
(click images to enlarge)
Like Technologic’s i.MX6-based TS-7970, the TS-7180 has a 122 mm x 112 mm footprint. Like its 119 x 94mm TS-7553-V2 SBC and sandwich-style, 75 mm x 55 mm TS-4100, it features the low power Cortex-A7 based i.MX6 UL, enabling the board to run at a typical 0.91 W.

Like the TS-4100, the new SBC includes an FPGA. On the TS-4100 this was described as a Lattice MachX02 FPGA with an open source, programmable ZPU soft core for controlling GPIO, SPI, I2C and daughtercards. Here, the manual mentions only that the unnamed FPGA enables the optional, 3x 16-bit wide quadrature counters, which are accessible via I2C registers. The “quadrature and edge-counter inputs provide access to” dual, optional tachometers, says Technologic.


 
TS-7180 (left) and block diagram
(click images to enlarge)
The quadrature counters and tachometers are part of a DAQ subsystem with screw terminal interfaces that is not available on its other i.MX6 UL boards. The digital acquisition features also include analog and digital inputs, DIO, and PWM.

Technologic boards typically have a lot of wireless options, but the TS-7180 goes even further by adding a cellular modem socket that supports either MultiTech or NimbeLink wireless modules. You also get Wi-Fi/BT, optional GPS, and a socket for Digi’s XBee modules, which include modems for RF, 802.15.4, DigiMesh, and more. There are also dual 10/100 Ethernet port with an optional Power-over-Ethernet daughtercard.


 
TS-7180 with cellular socket populated with NimbeLink wireless module (left) and with populated XBee socket
(click images to enlarge)
The TS-7180 ships with up to 1 GB RAM and 2 KB FRAM (Cypress 16 kbit FM25L16B), which “provides reliable data retention while eliminating the complexities, overhead, and system level reliability problems caused by EEPROM and other nonvolatile memories,” says Technologic. You also get a microSD slot and 4GB eMMC, which is “configurable as 2 GB pSLC mode for additional system integrity.”

The SBC provides a USB 2.0 host port, as well as micro-USB OTG and serial console ports. There’a also mention of a “coming soon” internal USB interface. Five serial interfaces, including TTL and RS485 ports, are available on screw terminals along with a CAN port.

Other features include an RTC and an optional enclosure and 9-axis IMU. The board runs on an 8-30V input with optional external power supply and Technologic’s TS-SILO SuperCap for 30 seconds of battery backup.

As usual, the board is backed up with open schematics and comprehensive documentation. If it wasn’t over our $200 limit, it would be included in our new catalog of 122 open-spec hacker boards. Two SKUs are available: a basic $315 model with 512MB RAM and a $381 model with 1GB RAM that adds GPS and IMU.

Specifications listed for the TS-7180 include:

  • Processor — NXP i.MX6UL (1x Cortex-A7 core @ up to 696MHz); FPGA
  • Memory/storage:
    • 512MB or 1GB DDR3 RAM
    • 2KB FRAM
    • 4GB MLC eMMC; opt. standard eMMC up to 64GB (special request)
    • MicroSD slot
  • Wireless:
    • 802.11b/g/n with antenna
    • Bluetooth 4.0 BLE
    • Cell modem socket (MultiTech or NimbeLink)
    • Optional GPS
    • XBee interface
  • Networking – 2x 10/100 Ethernet ports with optional PoE via daughtercard
  • Other I/O:
    • USB 2.0 host port
    • Micro-USB OTG port
    • Micro-USB serial console device port
    • 4x serial (1x TTL UART, 3x RS-232) via screw terminals
    • RS-485 (via screw terminal)
    • CAN (via screw terminal)
    • SPI, I2C headers
  • DAQ I/O:
    • 7x DIO (30 VDC tolerant) via screw terminal
    • 4x analog inputs (10V or 4-20 mA) via screw terminal
    • 4x digital inputs via screw terminal
    • PWM header
    • 2x optional quadrature counters
    • 2x Optional tachometers
  • Other features — battery backed RTC; temp. sensor; optional 9-axis accelerometer/gyro; TS-SILO Super Capacitor; optional enclosure
  • Power — 8-30 DC input; 0.91W typical consumption (0.59 min to 6.37 max); optional 24V external DIN-rail mountable “PS-MDR-20-24” power supply
  • Operating temperature — -40 to 85°C
  • Dimensions — 122 x 112mm
  • Operating system — Linux 4.1.15 kernel with Debian image

Further information

The TS-7180 is available in an engineering sampling program for $315 with 512 MB RAM or $381 model with 1GB RAM, GPS, and IMU. 100-unit pricing is $254 and $320. More information may be found in Technologic’s TS-7180 announcement and product page.

This article originally appeared on LinuxGizmos.com on January 4.

Technologic Systems | www.embeddedarm.com

 

Secure Cellular Router Serves Industrial and Transportation Needs

Digi International has announced the Digi WR54, a rugged, secure, high-performance wireless router for complex mobile and industrial environments. With dual cellular interfaces, Digi WR54 provides immediate carrier failover for near-constant uptime and continuous connectivity, especially as vehicles move throughout a city or for locations with marginal cellular coverage. Together with a hardened milspec-certified design and built-in Digi TrustFence security framework, this LTE-Advanced router is designed specifically to meet the connectivity challenges inherent in multi-location, on-the-move conditions, from rail and public transit to trucking fleets and emergency vehicle applications.

LTE-Advanced technologies with carrier aggregation are pushing theoretical download speeds to 300 Mbps, and the next generation of cellular radios is capable of aggregating three or more channels for capabilities up to 600 Mbps. It’s expected that 5G deployments this year will push the demands for performance and edge computing even further. Digi WR54 provides an LTE-Advanced cellular module built on a platform that supports higher speeds to optimize bandwidth today while also being positioned for the future as network capabilities improve.

Multiple transit system use cases require rugged, reliable, high-speed connectivity solutions to carry mission-critical data and communications. Transit system integrators require connectivity for fleet tracking, logistics, engine and driver performance monitoring, fare collection and video monitoring; rail companies that are building in wayside data capabilities need constant visibility into complex systems; industrial corporations like utility companies need to monitor high-value assets.

The Digi WR54 architecture supports these performance requirements with not just the aforementioned LTE-Advanced cellular module, but four Gigabit Ethernet ports for wired systems and the latest 802.11 ac Wi-Fi which combine to support the needs of any user. Other key features include:

  • Dual-core 880 MHz MIPS processor: designed with this high-speed architecture, the Digi WR54 is future-built with a CPU capable of supporting higher network speeds and capabilities as infrastructure is updated to support them
  • SAE J1455, MILSTD-810G and IP-54 rated: tested and certified to withstand water, dust, heat, vibration and other environmental challenges suitable to transportation and many industrial applications
  • Optional dual-cellular radios for continuous connectivity between carriers: for users that cannot afford downtime, if the primary cellular carrier drops out, the Digi WR54 automatically and immediately switches over to the secondary carrier
  • Digi TrustFence: a device-security framework that simplifies the process of securing connected devices and adapts to new and evolving threats
  • Digi Remote Manager: with this Digi web-based management tool, users can simply manage their devices, receive alerts and monitor the health of their deployed devices

For users looking to add high-speed passenger Wi-Fi to mass transit systems, the recently launched Digi WR64 dual LTE-Advanced cellular and dual 802.11ac Wi-Fi router offers an all-in-one mobile communications solution for secure cellular connectivity between vehicles and a central operations center. It offers a flexible interface design with integrated Wi-Fi for client and access point connectivity along with USB, serial, a four-port wired Ethernet switch, GPS and Bluetooth in order to consolidate multiple transit or industrial applications into a single, consolidated router.

Digi International| www.digi.com

Nordic Semi’s BLE SoC Selected for Ultra Low Power IoT Module

Nordic Semiconductor has announced that Nanopower has selected Nordic’s nRF52832 Bluetooth Low Energy (Bluetooth LE) System-on-Chip (SoC) to provide the wireless connectivity for its nP-BLE52 module, designed for developers of IoT applications with highly restricted power budgets.

The nP-BLE52 module employs a proprietary power management IC—integrated alongside Nordic’s nRF52832 Wafer-Level Chip Scale Package (WL-CSP) SoC in a System-in-Package (SiP)—which enables it to cut power to the SoC, putting it in sleep mode, before waking it up a pre-set time and in the same state as before it was put to sleep. In doing so the SoC’s power consumption in sleep mode is reduced to 10 nA, making it well suited for IoT applications where battery life is critical by potentially increasing cell lifespan 10x.

In active mode, the nRF52832 SoC runs normally. The SoC has been engineered to minimize power consumption with features such as the 2.4GHz radio’s 5.5mA peak RX/TX currents and a fully-automatic power management system. Once the Nordic SoC has completed its tasks, it instructs the nP-BLE52 to put it to sleep and wake it up again at the pre-set time. The nP-BLE52 then stores the Nordics SoC’s state variables and waits until the nRF52832 SoC needs to be powered up again. On wake-up, the device uploads the previous state variables, allowing the Nordic SoC to be restored to the same operational state as before the power was cut. The SoC’s start-up is much more rapid than if it was activated from a non-powered mode.

The nP-BLE52 module also features a low power MCU which can be set to handle external sensors and actuators when the Nordic chip is switched off. In this state, the module still monitors sensors and buffer readings and can trigger wake-ups if these readings are above predetermined thresholds, while consuming less than 1 uA. The nP-BLE52 also integrates an embedded inertial measurement unit (IMU).

The module’s power management is controlled through a simple API, whereby the user can predetermine the duration of the Nordic SoC’s sleep mode, set the wake-up time and date parameters, and select pins for other on/off triggers.

The module offers IoT developers several advantages, either extending battery life and/or reducing the size of the battery required to power the application thereby reducing the end-product footprint. Longer battery life also reduces or eliminates battery swaps and enables the developer to better adjust for remaining useful battery life as the battery discharges. The module is suitable for any battery-powered device which is not required to be constantly active, for example asset tracking, remote monitoring, beacons, and some smart-home applications.

The nRF52832 WL-CSP SoC measures just 3.0 mm by 3.2mm while offering all the features of the conventionally-packaged chip. The nRF52832 is a powerful multiprotocol SoC ideally suited for Bluetooth LE and 2.4 GHz ultra low-power wireless applications. It combines an 64 MHz, 32-bit Arm Cortex M4F processor with a 2.4 GHz multiprotocol radio (supporting Bluetooth 5, ANT, and proprietary 2.4 GHz RF software) featuring -96dB RX sensitivity, with 512kB Flash memory and 64kB RAM.

The WL-CSP SoC is supplied with Nordic’s S132 SoftDevice, a Bluetooth 5-certifed RF software protocol stack for building advanced Bluetooth LE applications. The S132 SoftDevice features Central, Peripheral, Broadcaster, and Observer Bluetooth LE roles, supports up to twenty connections, and enables concurrent role operation. Nordic’s unique software architecture provides clear separation between the RF protocol software and the developer’s application code, easing product development.

Nordic Semiconductor | www.nordicsemi.com

IoT Wireless Sensor Nodes Target LPWAN Deployments

Advantech has released its WISE-4210 series of IoT wireless sensor products, including a wireless LPWAN-to-Ethernet AP and three wireless sensor nodes. The nodes include tthe WISE-4210-S231 internal temperature and humidity sensor (shown), WISE-4210-S251 sensor node with 6-channel digital input and a serial port and WISE-4210-S214 sensor node with 4-channel analog input and 4-channel digital input. The device-to-cloud total solution provided by this series of LPWAN products allows IT, OT, and cloud platform system developers to easily implement a private LPWAN, acquire field site data, and achieve seamless integration with both public cloud, such as Microsoft Azure and private enterprise clouds.

Based on proprietary LPWAN technology, the new WISE-4210 series products minimize frequency band interference, support a wider data transmission range, are compatible with lithium batteries, and enable cloud platform integration. By locking the sub-GHz frequency band, WISE-4210 series products significantly reduce susceptibility to interference for 2.4 GHz wireless communication technologies such as Wi-Fi, Bluetooth and Zigbee.

By supporting a network transmission distance of up to 5 km, the WISE-4210 series meets the requirements of large-scale interior environments such as data centers, factories and warehouses for collecting and applying a wide range of interior data. With LPWAN technology, only three 3.6 V lithium batteries are required to operate the WISE-4210 sensor nodes for up to five years, eliminating the need for additional wiring and frequent recharging. Additionally, the WISE-4210 series supports multiple transfer protocols, including MQTT, RESTful, Modbus/TCP and Modbus/RTU, for simple device-to-cloud connections.

The WISE-4210-S231 sensor node with built-in temperature and humidity sensor collects relevant data form factories, data centers or warehouse management without requiring the installation of additional sensors or gateways, making it ideal for indoor temperature and humidity control applications. Meanwhile, the WISE-4210-S251 sensor node, which provides 6-channel digital input and a single RS-485 port, and the WISE-4210-S214 sensor node, which provides four-channel analog input and 4-channel digital input, can be used to collect electricity meter, pressure gauge, thermometer, and power consumption data from factory facilities.

The three wireless nodes support direct data transmissions to SCADA and cloud platforms through a WISE-4210-AP, eliminating the need for a separate data conversion device. The WISE-4210-AP access point is capable of managing up to 64 nodes simultaneously, and thus can simplify overall infrastructure and save installation space.

Advantech | www.advantech.com

Wireless Charging

Electric Field of Dreams

The concept of wireless charging can be traced all the way back to Nikola Tesla. Here, Jeff examines the background and principles involved in charging devices today without wires, and takes a hands-on dive into the technology.

By Jeff Bachiochi

________________________________________________________

Nikola Tesla is the recognized inventor of the brushless AC induction motor, radio, fluorescent lighting, the capacitor discharge ignition system for automobile engines and more. His AC power (with Westinghouse) beat out Thomas Edison’s DC power in the bid for the electrification of America. DC transmission is limited to miles due to its relatively low voltage and its transmission line loses. Thanks to the advent of the transformer, AC can be manipulated allowing higher voltages and higher efficiency power transmission. Today’s research in superconducting cable may be challenging these concepts—but that’s a story for another time.

Tesla wanted to provide a method of broadcasting electrical energy without wires. The Wardenclyffe Tower Facility on Long Island Sound was to be used for broadcasting both wireless communications and the transmission of wireless power. Tesla even viewed his research on power transmission as more important than its use as a method for communications. Unfortunately, Nikola was never able to make his vision a reality.
We think of Guglielmo Marconi as being the father of radio for his development of Marconi’s law and a radio telegraph system. He was able to obtain a patent for the radio using some of Tesla’s own ideas. It’s interesting to note that after Tesla’s death in 1946, the U.S. Supreme Court invalidated the Marconi patent because the fundamental radio circuit had been anticipated by Tesla. Again, not the direction of this article.
It was likely that Nikola’s work in far-field power transmission had not been fruitful due to propagation losses (inverse square law). Even today’s work on beam-formed, far-field transmissions are marginally successful. Transformers are successful because they operate in the near field. The close proximity between the primary and secondary coil and a well-designed magnetic energy path result in low energy losses in transformers.

Modern Wireless Charging
Today’s wireless charging systems for our portable devices are based on transformer operation. However, the primary and secondary coils are not in physical contact yet still transfer energy Figure 1. Efforts to maximize the magnetic field’s coupling exist, but this less-than-ideal coupling reduces the efficiency of the transfer—50% to 70% efficient. There are basically two methodologies today: inductive (tight) coupling (near field) and resonant inductive (loose) coupling (mid field). The resonant circuit allows an equivalent power to be transferred at a slightly greater distance.

Figure 1
The device is considered near-field (closely coupled) when the distance between the coils is less than the coils diameter. The mid-field device’s distance exceeds the coils diameter and relies on resonance to improve its power transfer.

Wireless efforts are in total flux with at least three organizations jockeying for position: The Wireless Power Consortium (WPC, induction), the Alliance for Wireless Power (A4WP, resonant) and Power Matters Alliance (PMA, induction). Interestingly, after WPC announced its plans to widen their specs to include resonant technologies, A4WP and PMA merged to become the AirFuel Alliance and now cover both technologies as well.

Beyond induction type, the biggest differences between the technologies is in control communication. Control of the charging process requires communications between transmitters and receivers. Induction technology uses in-band modulation of the RF signal to send and receive communications. Resonant induction technology uses Bluetooth for out-of-band communications. This makes the transmitter/receiver pair simpler but adds the complexity of Bluetooth. Since many receiving devices already have Bluetooth, this may be moot.

The Qi Standard
The WPC has coined the term Qi for their standard. If you search the web for wireless charging, this term pops up all over the place. This is not to say the AirFuel’s standard isn’t available—it seems to be a difference in promotional strategies. AirFuel has invested in getting their receivers into devices and their transmitters installed in public places. And while Qi receivers are also going into devices, their transmitters seem to be aimed at the individual. That means easy access to both Qi transmitters and receivers.
You can get the V1.2.2 specifications for the Qi standard from the WPC website. The current version (1.2.3) is available only to members now but should be public shortly. The two documents I received were “Reference Designs” and “Interface Definitions” for Power Class 0 specifications.

Power Class 0 aims to deliver up to 5 W of energy wirelessly via magnetic induction. This is accomplished by applying a fixed RF signal—generally in the 140 kHz range—into an inductive load (transformer primary). This is much like providing motor control using a half or full bridge, with the (transmitting) coil as the load instead of a motor.
Referring back to Figure 1, a receiver uses a similar coil (the transformer secondary). This coil supplies rectification circuitry with the voltage/current needed to power the receiver. The receiver can vary its load, which modulates the burden on the transmitting coil. Back at the transmitter, a change in the primary’s current can indicate when the secondary’s load is in range. Initially the transmitters remain relatively inactive, except for a periodic “ping” to look for a receiver. A normal ping will occur every
500 ms and last about 70 ms (Photo 1). Once in range the receiver gets secondary current and can self-power. During the last 50 ms of a ping, a receiver has a chance to communicate by modulating its load at 2 kHz rate (Photo 2). There are presently 16 messages it can choose to send.

Photo 1
This oscilloscope screenshot shows the “ping” transmissions of a wireless transmitter with no receiver in range.

Photo 2
Here we see a receiver sending a packet by modulating its load during the transmitter’s RF transmission.

Each message has four parts: a preamble, header, message and checksum. The preamble consists of from 11 to 25 “1” wake-up bits. The header is a 1-byte command value. The message length is fixed for each command, presently 1 to 8 bytes. The checksum is a 1-byte sum of the header and message bytes. All bytes in the header, message and checksum have an 11-bit asynchronous format consisting of a start bit (0), data bits (for example Command, LSB first), odd parity bit (OP) and stop bit (1). Each bit is sent using bi-phase encoding. Each bit begins with a state change in sync with its 2 kHz clock. The value of a bit is “0” when its logic states does not change during a 2 kHz clock period. If the state does change within that period, then the bit is a “1”.

The receiver has control over the transmitter. It initiates communication to send information and request power transfer. Back in Photo 2 you can see a Control Error Packet with a Header=0x03 and data=0x00. The signed value of the data indicates any difference between the requested and received current level.

While the receiver is in charge (ha!), the transmitter can acknowledge requests with 1 of 3 responses: ACK (accept), NAK (deny), or ND (invalid). Responses have no packet per se, but are merely a Frequency-shift keying (FSK) modulated pattern of 0s, 1s or alternating 0s and 1s. The receiver can request the depth of the FSK modulation from a list of choices between +/- 30 to 282 ns. The depth is defined as the difference in ns between the 1/Fop (operating frequency) and 1/Fmod (modulation frequency). The format is again bi-phase encoding in sync with the RF frequency. All bits begin with a change in modulation frequency. A “1” bit is indicated by a change in frequency after 256 cycles, while a ‘”0” bit has no change until the beginning of the next bit time. Responses are therefore easy for a receiver to demodulate.

So, communication is AM back-scatter from the receiver and FM on the base RF from the transmitter. The present specification defines three packets that can be sent by a transmitter in addition to the ACK, NAK and ND. These are informational and are formatted like the receiver packets, less the preamble.

System Control
From the transmitters point of view, it has 4 basic states: ping, ID, power transfer and selection. The transmitter is idle while in the ping state. Without some communication from a receiver, the transmitter will never do anything but ping. Once communication begins the receiver attempts to identify itself and become configured, at which point the transmitter can start power transfer. The transmitter will continue monitoring its feedback and change states when necessary. For instance, if communication is lost, it must cancel the power transfer state and begin to ping. The ability to detect foreign objects (FOD) is required for any system that can exceed 5W of power transfer. This parameter adds an additional 3 states to the basic 4 states: negotiation, calibration and renegotiation. When using FOD the negotiation state is required to complete identification, configuration and calibration. Calibration allows the transmitter to fine tune its ability to FOD. During the power transfer state, the receiver may wish to adjust its configuration. As long as no requests violate operational parameters, the power transfer state can continue. Otherwise the selection state will redirect further action. You can see how this works in the state diagram in Figure 2.

Figure 2
This is a general state diagram of the Qi standard for wireless chargers. Note two potential paths based whether or not foreign object detection is supported (required for greater than 5 W).

From the receiver’s point of view, it could be in an unpowered (dead) state prior to entering the transmitter’s field. Once within range, the short ping from a transmitter is sufficient to charge up its capacitive supply and begin its application programming. Its first order of business is to look for a legal ping, so it can properly time its first request 40ms after the beginning of a ping. The first packet is a signal strength measurement, some indication of transmitted energy. This is sufficient for the transmitter to enter the identification and configuration state by extending its RF timing and look for additional packets from the receiver. The receiver must now identify itself—version, manufacturer and whether or not it accepts the FOD extensions. A configuration packet will transfer its requirements as well as the optional packets it should expect. The transmitter digests all this data and will determined, based on the receiver’s ability to accept FOD extensions, whether it will proceed directly to the power transfer state or enter the negotiation state.

Packets must have a minimum of 7 ms silent period between each. The values sent in the configuration packet denote an official power contract between the transmitter and receiver. When the receiver doesn’t accept FOD extensions, it is this contract that the transmitter will abide by once it enters the power transfer state. If FOD extensions are enabled, it enters the negotiation state in an attempt to change the contract and provide higher power. The transmitter’s response lets the receiver know when a request to change a parameter is acceptable. This way both receiver and transmitter agree on the power contract it will use when negotiations are closed.

Once negotiations have ended, the calibration state is entered. The calibration consists of multiple packets containing received power values measured by the receiver while it enables and disables its load (maximum and minimum power requirements). This provides the transmitter with some real use values so it can better determine FOD.
During the power transfer (PT) state, the receiver must send a control error packet every 250 ms that the transmitter uses to determine its operating (PID) parameters. Meanwhile, received power packets are sent every 1,500 ms. Without this feedback, the transmitter will drop out of the PT state. Other packets can affect the PT state as well—most notably an end power packet. This may be due to a full charge or other safety issue and the transmitter drops out of the PT state. At this point a receiver can cease communication and while the transmitter will begin pinging, the receiver can rest indefinitely.

Sense, Configure, Charge
I’ve found that the Qi receivers with micro USB connectors make it easy to add wireless charging to your phone or tablet. One of these fits inside my Motorola phone with only the smallest bump of the connector on the outside. My Amazon Fire is not so lucky. It had to stay on the outside (Photo 3).

Photo 3
Shown on the left, the Amazon Fire required me to add the Qi receiver to the outside. It’s covered with a very large band-aid. On the right, my Motorola phone had room inside. The only clue is the receiver’s minimally obtrusive micro USB connector.

Adafruit has a module available that has no connector and is not enclosed in a skin (Photo 4). You can see in that photo that a receiver requires very few external components. This one uses a Texas Instruments bq51013B, which is less than $4. One advantage to choosing this device is the non-BGA version which is appealing to the DIYer that wants to hand solder the device onto a PCB.

Photo 4
You can see how few components are required on the Adafruit Qi wireless receiver shown here on a wireless transmitter. The voltmeter shows a voltage output of 4.98 V.

I suggest that you use high strand, flexible wires when making connections to this because a stiff wire can cause undue stress on flexible circuitry. I want to use this wireless charge receiver to keep some of my robots charged. To do this, the robot has to ride over the top of a transmitter. The receiver would then recharge the on-board battery or batteries. I’ve chosen to use Li-ion batteries because they have a high power-to-weight ratio. They also have a relatively flat discharge curve. Unfortunately, a single cell 3.7-V Li-ion battery is not sufficient to power most motors. Therefore, multiple cells must be used.

When multiple cells are in series the charging becomes an issue because the cells should be charged using a balanced charger to prevent charge imbalance. Charging cells in series as a group cannot prevent the over/under charging of individual cells. This means one of two approaches: Use a single cell and use a boost power converter to obtain your necessary voltage, or use a more complicated multi-cell, balanced charger with a boost converter between the wireless receiver and the charger’s input.
Upon contemplating the pros and cons of each method, I’ve decided to use a modular approach by treating each battery as a separate entity. The simplest charging IC I could find was STMicroelectronics’ STC4054. This is a TSOT23-5L (5-pin) device that requires only one external component to set the charging rate. This is important because some chargers will allow very high currents and I will be sharing the current for all chargers via one wireless receiver. While these can handle 1 A, if I want to say, charge four Li-ion batteries in series I need to limit each charging circuit to 250 mA (250 X 4 = 1,000) or I run the risk of the wireless receiver becoming overloaded and everything will shut down.

The STC4054 has a charging voltage of 4.2 V using the maximum of whatever current you set by the resistor you choose from the PROG pin to ground using the following formula:

rearranging we get…

A minimum VCC of 4.25 V is sufficient to sustain a complete charge cycle. Here is a breakdown of the whole charge cycle: If the battery voltage is below 2.9 V it will be trickle charged at 1/10 of IBAT. Once it reaches 2.9 V it enters the constant current mode charging at IBAT. Once it reaches 4.2 V it switches to constant voltage mode to prevent over charging. The cycle ends when the current drops to less than 1/10 of IBAT. Should the battery voltage fall below 4.05 V, a charging cycle will begin to maintain the battery capacity to a value higher than 80%.

The STC4054 is thermally protected by reducing the charging current should the temperature approach 120°C. The package leads are the main heat conductors from the die, so sufficient copper areas on the PCB will help with heat radiation. The device will max at 800 mA, but is spec’d to handle 500 mA at 50°C. You can expect stability without additional compensation unless you have long leads to the battery. A 1 µF to 4.7 µF capacitor can be added to the BAT connection if necessary.

The CHRG pin is an open-collector output which can be monitored to indicate when the IC is in the charging state. It will pull down an LED if you wish a visual status indicator. This IC will cost you about $1.50. With no voltage applied to the IC, it will go into a power down mode with a drain of only 17 µA on the battery.

Now this circuit takes care of charging a single battery, and we might have up to four in series. It’s the series part that is the problem because only the first can have a reference to ground. Since the wireless receiver is designed to produce a 5 V output, this is easily connected to the first charging circuit. We could try and get fancy with a boost converter to get a 20 V output to feed the four chargers with their inputs in series, but this has all kinds of bad karma associated with it. Fortunately, there is a rather inexpensive solution: Use isolated DC-DC converter modules. All converter inputs are in parallel on the wireless chargers output. Each of the converters’ outputs can be tied to a separate charging circuit. Since each of the converters’ outputs are isolated from its inputs, there is no reference to ground—the minus output of the wireless receiver). That means they can then be used to charge batteries which are connected in series.

The circuit given in Figure 3 shows four changing circuits—each (potentially) using its own isolated 5 VDC to 5 VDC converter. These are available in 1 W to 3 W SIP-style packages and cost from $3 to $10 each. Modules with high current (greater than 3W) are available, but the package style changes to DIP. Their inputs are in parallel with a connector meant to go to the wireless charging receiver. There are a lot of jumpers used to select how the outputs of each charging circuit are to be connected to output connectors. Each charger can charge one Li-ion battery using a standard two-pin 1S1P (one series cell, one parallel cell) connector. Or you can jumper them in series, which uses the standard connectors for 2S1P, 3S1P and 4S1P (series cells).

Figure 3
This schematic shows four Li-ion cell charging circuits using the STC4054. The input to each IC can come from an optional isolated source when using a DC-DC converter from RECOM. If each of the charging circuits are isolated, they can be applied to separate Li-ion cells in series.

You’ll note that multi cell Li-ion battery packs usually come with two connectors—one for use and one for charging. The charging connector contains a wire to each battery junction to allow cell-balanced charging (Photo 5). Battery packs that feature balanced charging usually contain the JST HX connector for charging. The power contacts are another story. They may be JST HSNG style, Dean’s connector or other specialty types.

Photo 5
There seems to be some standardization on balanced Li-ion cell chargers. They require a common plus 1 wire for each cell so each cell can be monitored and charged independently. This means any battery pack with more than one cell requires separate connectors for charging and discharging.

Small Bots ‘n Bats
You’ll find plenty of the small robot bases using AA batteries with a UNO or some other micro platform as its controller. There is nothing wrong with these inexpensive platforms for educational purposes. With a fresh set of batteries, you will usually have predictable behavior. In rather short order however, things will begin to go loony. The motor load will begin to affect the controller as the battery voltage dips. Even at 6 V, with a low drop out regulator, the controller operation and any sensors will quickly become unpredictable. This can be truly a frustrating time for the newbie, as one searches their code for a logic error that might produce the inappropriate action observed, when actually there may be nothing wrong!

You can save a lot of heartache if you just add an extra battery (or two) to raise the voltage to 7.5 V or even better 9 V. I’ve seen kids quickly lose interest or give up entirely simply because they don’t understand what’s happening. I’ve found a better solution is to replace the AAs with a couple of Li-ion 18650 type 3.7 V cells. The 18650 looks like an over-sized AA battery and has battery holders that are similar (Photo 6). You can expect about 2,000 mA-hours from AA cells. The 18650 Li-ion cells pack about three times the energy and they can be popped out and recharged in a few hours. Li-ion flat packs can also be used here, but they are not as “universal” as the 18650 single cells.

Photo 6
Replacing four AA cells with two 18650 Li-ion cells can save a lot of head scratching when unexpected behavior is due to battery droop. The AA cells (4 x 1.5 V) does not leave much headroom when a 5 V regulator is used. Not only is the discharge curve relatively flat for Li-ion cells (2 x 3.7 V) preventing drops in regulation, but the 18650 packs 3 times the energy.

It is a good idea to remove batteries from any equipment that will not be used for extended periods of time. Many devices today—like the ones with auto off functions—have parasitic circuits that continue to draw minuscule currents even when “off”. These will continue to draw down your batteries until they are unusable. Even though Li-ion cells have a protective circuit that prevents them from being discharged below a safe level—approximately 2.75 V/cell—this internal circuitry is parasitic and acts as a tiny load. While self-discharge is only a few percent per month, once the cell voltage drops below a critical voltage this circuitry may not allow it to be recharged. So always store a rechargeable in a “charged” state.

Wireless Charging today
Wireless charging is only in its infancy. Today’s phone chargers are typically less than 5 W. But there is work being done on higher rated equipment. It is proper that these low power devices have such safeguards built-in to prevent unwanted catastrophes. We know from the not too distant past that, along with higher power density materials, comes the potential for calamity unless the proper safeguards are in place. Public education can limit the misuse and/or abuse of lithium technology, just as it has for the safe handling and use of gasoline.

In order for the electric vehicle to become useful, we will need to replenish its range-defining battery charge in fairly short order. This requires extreme infrastructure changes. You can tell by the size of the connectors and cable required for this process that this is high power. The holy grail is for this to happen wirelessly and automatically. From a simple pad embedded in ground where you park your vehicle, to a highway infrastructure that transfers power to your vehicle while you drive. Wireless power transfer is here to stay. Nikola Tesla must be at peace knowing that his work is beginning to bear fruit.

Additional materials from the author are available at:www.circuitcellar.com/article-materials

RESOURCES

Adafruit | www.adafruit.com
RECOM | www.recom-power.com
STMicrolectronics | www.st.com
Texas Instruments | www.ti.com

See the article in the May 334 issue of Circuit Cellar

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

Note: We’ve made the October 2017 issue of Circuit Cellar available as a free 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.