October Circuit Cellar: A Sneak Preview

The October issue of Circuit Cellar magazine is on the launch pad, ready to deliver a selection of excellent embedded electronics articles covering trends, technology and design.

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Here’s a sneak preview of October Circuit Cellar:

TECHNOLOGY FOR DRONES / ROBOTIC HAND

Commercial Drone Design Solutions Take Flight: Chips, Boards and Platforms
The control, camera and comms electronics inside today’s drones have to pack in an ambitious amount of functionality. Circuit Cellar Chief Editor Jeff Child explores the latest Oct 327 Coverand greatest chip and module solutions serving today’s commercial and consumer drone designs.

Building a Robot Hand: With Servos and Electromyography
Learn how three Cornell University students developed a robotic hand. The system captures impulses generated by muscle contractions and then filters and feeds those signals to a microcontroller which controls finger movement.

 

CAN’T STOP THE SIGNAL

Signal Chain Tech Pushes Bandwidth Barriers: ADCs, FPGAs and DACs
FPGAs and D-A converters are key  technologies making up a signal chain. Here, Circuit Cellar Chief Editor Jeff Child steps through the state-of-the-art options available for crafting efficient, highly-integrated signal-centric systems.

Antenna Performance Measurement Made Easy: Covering the Basics
If you’re doing any kind of wireless communications design, chances are you’re including an antenna. Columnist Robert Lacoste shows how the task of measuring an antenna’s performance is less costly and exotic than you’d think.

MONITORING GEAR WITH MICROCONTROLLER BRAINS

Gas Monitoring and Sensing (Part 1): Fun with Fragrant Analysis
Columnist Jeff Bachiochi covers the background issues surrounding gas monitoring and sensing. Then he describes how he uses sensors, A/D conversion and Arduino technologies to do oxygen measurement.

Logger Device Tracks Amp Hours (Part 1): Measuring Home Electricity
Setting out to monitor and log electricity usage in his house, Bill Wachsmann built an amp-hour logger using a microcontroller and a clamp on ammeter.

KEEPING THE LEGACY ALIVE

Emulating Legacy Interfaces: Do it with Microcontrollers
There’s a number of important legacy interface technologies—like ISA and PCI—that are no longer supported by the mainstream computing industry. In his article Wolfgang Matthes examines ways to use microcontrollers  to emulate the bus signals of legacy interconnect schemes.

Building a Retro TV Remote : PIC MCU-Based Design
Dev Gualtieri embarks on building a retro-style TV remote, based on a Microchip PIC microcontroller. He outlines the phototransistor, battery and software designs he made along the way.

AND MORE FROM OUR EXPERT COLUMNISTS:

Get in the Loop on Positive Feedback: New Value in an Old Concept
Positive feedback loops are an important element of modern circuitry such as crystal oscillators, PLLs and other devices. Here, George Novacek goes deep into the math and circuit analysis of positive feedback and how it’s used in electronics.

Build an Embedded Systems Consulting Company (Part 6): Trade-Offs of Fixed-Price Contracts
Continuing his “Building an Embedded Systems Consulting Company” article series, this month Bob Japenga explores the nature of contracts and how fixed price contracts can be an effective, albeit dangerous tool in marketing.

Microchip Adds AVR and SAM MCUs to Programming Service

Microchip Technology , has expanded its custom programming service to include AVR and SAM microcontrollers (MCUs). Users can add their custom code to MCUs from more than 30 AVR and SAM families, along with nearly all PIC MCUs and memory devices, directly from the manufacturer via microchipDIRECT.  Microchip  provides an online custom programming service to all of its clients.

Microchip’s custom programming service is available to any client regardless of their order size and can be used throughout the development process. From a7be46ac521844589d6de789549e7c153very small runs to verify that the code is working, all the way up through full-scale production runs, this cost-effective programming service offers customers the flexibility to add their code to any order size, from one device to millions. Additionally, each first verification order is complimentary and includes three free samples programmed to each client’s exact specifications.

To get started, clients choose their part number on microchipDIRECT and then add their code and other configuration settings, shown on the intuitive online form, directly into the encrypted website. The MCUs will then be programmed directly by Microchip with no need to involve a third party programming or manufacturing facility, thus eliminating the risk of code exposure during the programming process.

In addition to custom programming services, microchipDIRECT also offers value-added services such as tape and reeling, labels, ink dotting and more. With the largest inventory of Microchip products in the industry, microchipDIRECT provides a full service channel for all purchasing needs. The mobile-optimized website also offers global support in ten languages, volume pricing, live service agents, numerous payment options and order notifications for customer convenience. For more information visit www.microchipdirect.com.

Custom programming directly from Microchip is available for nearly all PIC MCUs and more than 30 AVR and SAM families with additional device support rolling out over the next year. For more information about this custom programming service, visit: www.microchipdirect.com/avr-sam-programming.html

Microchip Technology | www.microchip.com

Time-Oriented Task Manager

…for 8-bit PIC Microcontrollers

For many new embedded applications, an 8-bit MCU is just right. Pedro
shows how to build a time-oriented task manager using Microchip’s PIC
16F628A 8-bit microcontroller.

By Pedro Bertoleti

Microcontrollers are everywhere. From a simple remote control to an advanced car embedded system, microcontrollers surround us all. But while an 8-bit microcontroller is a relatively simple device, the software on them can get more sophisticated as more functionality is added to embedded systems. One of the most interesting advances in software technique is managing tasks. That involves enabling a microcontroller to execute several scheduled tasks, ensuring periodic and precise time execution. Here, we will examine how to implement a time-oriented task manager for a simple microcontroller—in this case, a Microchip 8-bit PIC microcontroller.

A graphic representation of a time-oriented task manager and its tasks

A graphic representation of a time-oriented task manager and its tasks

A good place to start is to ask: What is a task? A task is a part of a software program that’s dedicated to do something exclusively. In other words, a task is a piece of software that can be implemented and executed as an independent software program. Take, for example, an embedded system that has to blink an LED, send something through the UART interface and check an input’s state. Each one of these activities can be defined as a task. In a general way, each function of an embedded system can be defined as a task. A time-oriented task manager is a piece of software that performs these three main activities:

  • Execute tasks periodically
  • Execute tasks in the amount of time specified for them
  • Ensure time-precision measurement for the execution of tasks

In terms of coding, the time-oriented task manager and the tasks are different parts of the same software program. ….

Read the full article in the September 326 issue of Circuit Cellar

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September Circuit Cellar: A Sneak Preview

The September (326) issue of Circuit Cellar magazine serves up a meaty selection of useful technology resources along with inspiring, interesting embedded electronics design articles.

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cclogo_2013_header

Here’s a sneak preview of September Circuit Cellar:

FOCUS ON MICROCONTROLLERS

Getting Started with PSoC Microcontrollers (Part 3): Data Conversion, Capacitive Sensing and More
In Part 3, Nishant Mittal gets into some if the PSoC’s more complex features like Data Conversion.

Implementing a Time-Oriented Task Manager for 8-bit PIC Microcontrollers
Pedro Bertoleti shows readers how to build a time-oriented task manager using Microchip’s PIC 16F628A 8-bit microcontroller.

SPECIAL SECTION: EMBEDDED SECURITY

Microcontrollers Beef Up Security Features: Defense in a Connected World
Jeff Child explores the various flavors of embedded security features that microcontroller vendors are adding to their devices.

Resources for Embedded Security: Hardware, Software and Services
Circuit Cellar collects four pages worth of info about companies that provide embedded security products, tools and services.

TECHNOLOGY FEATURES

Using Power Audio Amplifiers in Untypical Ways (Part 1): Best Building Blocks
Petre Petrov shows readers how to use PAAs as universal building blocks to create analog signal generators, analog power supplies, voltage splitters and more.

Data Acquisition Advances Focus on Interfacing
Jeff Child discusses the latest data acquisition solutions, with a look at how interface technologies have evolved.

Future of IoT Communications: Will Upgraded Cellular Networks Benefit IoT?
This guest essay by Andrew Girson, CEO of Barr Group, explores how IoT will fare in the 5G network era.

MORE FROM OUR EXPERT COLUMNISTS:

Block Diagram Reduction and Automatic Tuning
George Novacek steps through how to think in terms of block diagrams to help you reduce system complexity early on in a design.

Numeric Precision vs. DDS Calculations
Using the full frequency resolution of a DDS chip outstrips the capabilities of floating point numbers. Ed Nisley looks at high-res frequency calibration and measurements in the DDS realm.

Deadbolt the Uninvited: Locked Out of My Home
In this Part 2 of Jeff Bachiochi’s electronic lock story, he gets into some of the power and remote-control issues of his electronic deadbolt lock project.

Diagnosing Performance Variations in HPC
Ayse K. Coskun delves into how application performance variations can cause inefficiency
in high-performance computing (HPC) systems and how to diagnose these variations.

Microchip Launched Two New MCU Families

Microchip Technology has made available its new SAM D5x and SAM E5x microcontroller (MCU) families. These new 32-bit MCU families offer extensive connectivity interfaces, high performance and robust hardware-based security for a wide variety of applications. The SAM D5/E5 MCUs combine the performance of an ARM Cortex-M4 processor with a Floating Point Unit (FPU). This combination offloads the Central Processing Unit (CPU), increasing system efficiency and enabling process-intensive applications on a low-power platform.

35352057604_77bb4aab93_m

Running at up to 120 MHz, the D5x and E5x MCUs feature up to 1 MB of dual-panel Flash with Error Correction Code (ECC), easily enabling live updates with no interruption to the running system. Additionally, these families are available with up to 256 KB of SRAM with ECC, vital to mission-critical applications such as medical devices or server systems.

These new MCUs have multiple interfaces that provide design flexibility for even the most demanding connectivity needs. Both families include a Quad Serial Peripheral Interface (QSPI) with an Execute in Place (XIP) feature. This allows the system to use high-performance serial Flash memories, which are both small and inexpensive compared to traditional pin parallel Flash, for external memory needs.

The SAM D5/E5 devices also feature a Secure Digital Host Controller (SDHC) for data logging, a Peripheral Touch Controller (PTC) for capacitive touch capabilities and best-in-class active power performance (65 microA/MHz) for applications requiring power efficiency. Additionally, the SAM E5 family includes two CAN-FD ports and a 10/100 Mbps Ethernet Media Access Controller (MAC) with IEEE 1588 support, making it well-suited for industrial automation, connected home and other Internet of Things (IoT) applications.

Both the SAM D5x and E5x families contain comprehensive cryptographic hardware and software support, enabling developers to incorporate security measures at a design’s inception. Hardware-based security features include a Public Key Cryptographic Controller (PUKCC) supporting Elliptic Curve Cryptography (ECC) and RSA schemes as well as an Advanced Encryption Standard (AES) cipher and Secure Hash Algorithms (SHA).

The SAM E54 Xplained Pro Evaluation Kit is available to kick-start development. The kit incorporates an on-board debugger, as well as additional peripherals, to further ease the design process. All SAM D5x/E5x MCUs are supported by the Atmel Studio 7 Integrated Development Environment (IDE) as well as Atmel START, a free online tool to configure peripherals and software that accelerates development. SAM D5x and SAM E5x devices are available today in a variety of pin counts and package options in volume production quantities. Devices in the SAM D5/E5 series are available starting at $2.43 each in 10,000 unit quantities. The SAM E54 Xplained Pro Evaluation Kit is available for $84.99 each.

Microchip | www.microchip.com

August Circuit Cellar: A Sneak Preview

The August (325) issue of Circuit Cellar magazine is jammed packed with useful technical information and inspiring, intriguing embedded electronics design stories.

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Here’s a sneak preview of August Circuit Cellar:

FUN WITH GUITAR AMPLIFIERS!

Digital Guitar Amplifier/ Effects Processor—Part 2
Brian Millier details the digital guitar amplifier/effects unit he built using two Teensy Arduino modules.

A Range of Power Supplies for Hollow-State Guitar Amplifiers
Richard Honeycutt compares several different power supplies used for hollow-state guitar amplifiers.

MICROCONTROLLERS & PROCESSORS!

Firmware Upgrade with the PIC32
Nick Sicalides delves into performing firmware upgrades using a bootloader on the Microchip PIC32

Getting Started with PSoC Microcontrollers (Part 2): Putting PSoC to Work
Nishant Mittal goes even deeper on the Cypress PSoC providing some useful design examples.

Moore’s Law and the Chip Industry’s Perfect Storm
In this Interview Q&A Krste Asanovic explains RISC-V and the open sourcing of processor architecture.

SECURITY & RELIABILITY & ENCRYPTION!

Power Analysis of a Software DES Encryption Routine
Columnist Colin O’Flynn examines how to break a software implementation of the DES security routine.

Reliability and Failure Prediction: A New Take
Craig Armenti and Dave Wiens discuss a better way to simulate PCB vibration and acceleration.

Preventing Unwanted Entry
Columnist Jeff Bachiochi takes us inside his exploration of electronic lock systems, getting down to the fine details.

Future of Embedded Security: Wi-Fi to the Danger Zone
This guest essay by Adam Cecchetti, CEO of Deja vu Security, explains how memory leaks in your embedded system could have life or death consequences.

AND MORE FROM OUR EXPERT COLUMNISTS:

Automatic Control (Part 4) The Implementation
George Novacek describes the PID temperature controller he built for a meat smoker.

Fully Differential Amplifiers
Robert Lacoste sings the praises of fully differential amplifiers and presents a few designs using them.

Build an Embedded Systems Consulting Company (Part 5) Axiom Wrap-Up
Bob Japenga shares more insights on running a successful embedded design firm built to last.

Microchip Sequential Linear LED Driver Targets Offline Lighting

A next-generation sequential linear LED driver for offline lighting applications is now available from Microchip Technology. The CL88020, an extension of Microchip’s CL88XX family, is designed to drive a long string of low-cost LEDs directly from the 120 VAC line input. The product allows customers to create reliable, cost-effective and compact LED lighting applications by having High Power Factor (PF) without the need for switch-mode power conversion which is typically required for LED lighting design.

35630062231_5f1dbbeab8_b

The CL88020 was designed to minimize driver circuit component count to allow for a very small and efficient design. The simple design allows for a single-layered Printed Circuit Board (PCB) design. Unlike the conventional AC-DC switch mode power supply, the basic driver circuit consists of the CL88020 IC, two small ceramic capacitors and a bridge rectifier only. High-voltage capacitors, transformer or inductors, electromagnetic interference (EMI) filters or Power Factor Correction (PFC) circuitry are not required. This allows for a smaller solution size and a lower overall bill of material (BOM) cost as compared to traditional LED solutions.

Microchip | www.microchip.com

Simplified Interfacing to High-Speed Infotainment In-Vehicle Networks

Microchip Technology recently announced a new high-speed network solution for in-vehicle infotainment with device control over Internet Protocol (IP). Unified Centralized Software Stack (UNICENS) is a free software module for anyone using Intelligent Network Interface Controllers (INIC), such as the OS81118, OS81119, and any future INICs. It enables you to focus on application development rather than network management.

Microchip UNICENS
With UNICENS, you can choose your preferred device control method including Media Oriented Systems Transport (MOST) technology’s FBlock, Ethernet IP and customer-specific methods. It also supports the configuration and control of all network participants from one central node. Furthermore, you don’t need microcontrollers in all the other nodes in the network. UNICENS is currently available as open-source software for Microchip customers.

Microchip Technology | www.microchip.com

Registration Opens for 19th Annual Worldwide MASTERs Conference

Microchip Technology Inc., a leading provider of microcontroller, mixed-signal, analog and Flash-IP solutions, today announced that registration is open for its 19th annual Worldwide MASTERs Conference at the JW Marriott Desert Ridge Resort in Phoenix, AZ.  The Main Conference takes place from August 19 to 22, 2015. The Pre-Conference is held on August 17-18, 2015.Microchip video MASTERS

The MASTERs Conference provides design engineers with an annual forum for sharing and exchanging technical information about Microchip’s 8-, 16-, and 32-bit PIC microcontrollers, high-performance analog and interface solutions, dsPIC digital signal controllers, wireless and mTouch sensing solutions, memory products, and MPLAB development systems—including the industry’s only singular IDE to support an entire 8-, 16-, and 32-bit microcontroller portfolio.


There is a broad range of class offerings for 2015, to meet the growing needs of software and hardware design engineers and engineering managers, with more than 100 classes being offered—39 of which are new this year.  In addition to lecture-based classes, there are 47 hands-on workshops that enable attendees to learn more about specific applications by using development tools and writing code in the classrooms.  Classes are available for engineers with advanced experience or little knowledge in the concepts and basics of the technology being discussed.

Based on its overwhelming success at previous MASTERs, Microchip is again offering a two-day Pre-Conference for those who wish to attend as many classes as possible during the week. These classes are also designed for beginner through advanced attendees. For example, “Introduction to Embedded Programming Using C” is a two-day, 16-hour, step-by-step crash course in C, with practical hands-on exercises.

MASTERs classes cover a wide range of electronic-engineering topics, including connectivity sessions on Ethernet, TCP/IP, USB, CAN and wireless (e.g., Bluetooth and Wi-Fi), graphics and capacitive-touch interface development, intelligent power supplies, firmware development, motor control, selecting op amps for sensor applications, DSP and using an RTOS.

Additional activities include networking sessions between third-party partners and attendees to discuss relevant design topics, meeting with third-party development tool experts and a simulated wafer fab plant tour.

Entry to the MASTERs Conference courses, a USB Flash Drive with all class materials, round-trip airport transportation, accommodations for three nights with meals, evening entertainment, and more are included in the Conference cost of $1,526, if you register by May 8, 2015 to receive the Early Bird Discount.

Source: Microchip Technology

 

GestIC Controller Enables One-step Design-in of 3-D Gesture Recognition

Microchip Technology recently announced a new addition to its patented GestIC family. The new MGC3030 3-D gesture controller features simplified user-interface options focused on gesture detection, enabling true one-step design-in of 3-D gesture recognition in consumer and embedded devices. Housed in an easy-to-manufacture SSOP28 package, the MGC3030 expands the use of 3-D gesture control features to high-volume, cost-sensitive applications such as audio, lighting, and toys.GestIC

The simplicity of gesture-detection integration offered by the MGC3030 is also achieved through Microchip’s free, downloadable AUREA graphical user interface (GUI) and easily configurable general-purpose IO ports that even allow for host MCU/processor-free usage. The MGC3030’s on-chip 32-bit digital signal processor executes real-time gesture processing, which eliminates the need for external cameras or controllers for host processing and allows for faster and more natural user interaction with devices.

The MGC3030 makes full use of the GestIC family development tools, such as Microchip’s Colibri Gesture Suite, which is an on-chip software library of gesture features. Intuitive and natural movements of the human hand are recognized, making the operation of a device functional, intuitive, and fun. Without the need to touch the device, features such as Flick Gestures, the Air Wheel, or the proximity detection perform commands such as changing audio tracks, adjusting volume control or backlighting, and many others. All gestures are processed on-chip, allowing manufacturers to realize powerful user interfaces with very low development effort.

Unique to GestIC technology, the programmable Auto Wake-Up On Approach feature begins operating in the range of 100-µW power consumption, enabling always-on gesture sensing in power-constrained applications. If real user interaction is detected, the system automatically switches into full sensing mode and alternates back to auto wake-up mode once the user leaves the sensing area. These combined features and capabilities provide designers with the ability to quickly integrate gesture detection features at price points that are ideal for high-volume devices.

Also available is Microchip’s Woodstar MGC3030 Development Kit (DM160226). The $139 kit is available via any Microchip sales representative, authorized worldwide distributor, or microchipDIRECT (www.microchip.com/Dev-Kit-012015a). The kit comes with the AUREA GUI, the central tool to parameterize the MGC3030 and the Colibri Suite to suit the needs of any design. AUREA is available via a free download at www.microchip.com/AUREA-GUI-012015a. The Colibri Gesture Suite is an extensive library of proven and natural 3-D gestures for hands and fingers that is preprogrammed into the MGC3030.

The MGC3030 featuring GestIC technology is available in a 28-pin SSOP package. Each unit costs under $2 each in high volumes.

Source: Microchip Technology

Liquid Flow Sensor Wins Innovation Prize

Sensirion recently won the DeviceMed OEM-Components innovation prize at the Compamed 2014 exhibition. The disposable liquid flow sensor LD20-2000T for medical devices features an integrated thermal sensor element in a microchip. The pinhead-sized device is based on Sensirion’s CMOSens technology.sensirionliquidflowsensor

The LD20-2000T disposable liquid flow sensor provides liquid flow measurement capability from inside medical tubing (e.g., a catheter) in a low-cost sensor, suitable for disposable applications. As a result, you can measure drug delivery from an infusion set, an infusion pump, or other medical device in real time.

A microchip inside the disposable sensor measures the flow inside a fluidic channel. Accurate (~5%) flow rates from 0 to 420 ml/h and beyond can be measured. Inert medical-grade wetted materials ensure sterile operation with no contamination of the fluid. The straight, open flow channel with no moving parts provides high reliability. Using Sensirion’s CMOSens technology, the fully calibrated signal is processed and linearized on the 7.4 mm2 chip.

Source: Sensirion

Embedded Chip = Subdermal Chip?

Forget stashing your cash under your mattress. Now you can stash it under your skin. Sort of.

The Telegraph reported Tuesday that Martijn Wismeijer, a Dutch innovator, recently implanted a 12-mm xNTi NFC chip in his body to store Bitcoin. The small glass chip stores 888 bytes and comes with a syringe for installation.

According the Dangerous Things site, the kit includes:

  • Glass chip preloaded in EO gas sterilized injector
  • A skin antiseptic
  • Gauze pads, a bandage, and non-latex surgical gloves

 

Source: Telegraph

Eco-Friendly Home Automation Controller

The 2012 DesignSpark chipKIT Challenge invited engineers from around the world to submit eco-friendly projects using the Digilent chipKIT Max32 development board. Manuel Iglesias Abbatemarco of Venezuela won honorable mention with his autonomous home-automation controller. His design enables users to monitor and control household devices and to log and upload temperature, humidity, and energy-use sensor data to “the cloud” (see Photo 1).

The design comprised a Digilent chipKIT board (bottom), my MPPT charger board (chipSOLAR, middle), and my wireless board (chipWIRELESS, top).

Photo 1: The design comprised a Digilent chipKIT board (bottom), my MPPT charger board (chipSOLAR, middle), and my wireless board (chipWIRELESS, top).

The system, built around the chipKIT Arduino-compatible board, connects to Abbatemarco’s custom-made “chipSOLAR” board that uses a solar panel and two rechargeable lithium-ion (Li-on) cells to provide continuous power. The board implements a maximum power point tracking (MPPT) charger that deals with a solar panel’s nonlinear output efficiency. A “chipWIRELESS” board integrating a Quad Band GSM/GPRS modem, an XBee socket, an SD card connector, and a real-time clock and calendar (RTCC) enables home sensor and cloud connectivity. The software was written using chipKIT MPIDE, and the SD card logs the data from sensors.

“Since the contest, I have made some additions to the system,” Abbatemarco says. “The device’s aim is uninterrupted household monitoring and control. To accomplish this, I focused on two key features: the power controller and the communication with external devices (e.g., sensors). I used DesignSpark software to create two PCBs for these features.”

Abbatemarco describes his full project, including his post-contest addition of a web server, in his article appearing in Circuit Cellar’s May issue. In the meantime, you’ll find descriptions of his overall design, power management board, and wireless board in the following article excerpts.

DESIGN OVERVIEW
The system’s design is based on a Digilent chipKIT Max32 board, which is an Arduino-compatible board with a Microchip Technology 32-bit processor and 3.3-V level I/O with almost the same footprint as an Arduino Mega microcontroller. The platform has all the computational power needed for the application and enough peripherals to add all the required external hardware.

I wanted to have a secure and reliable communication channel to connect with the outside world, so I incorporated general packet radio service (GPRS). This enables the device to use a TCP/IP client to connect to web services. It can also use Short Message Service (SMS) to exchange text messages to cellular phones. The device uses a serial port to communicate with the chipKIT board.

I didn’t want to deal with cables for the internal-sensor home network, so I decided to make the system wireless. I used XBee modules, as they offer a good compromise between price and development time. Also, if properly configured, they don’t consume too much energy. The XBee device uses a serial port to communicate with the chipKIT board.
To make the controller”green,” I designed a power-management board that can work with a solar panel and several regulated DC voltages. I chose a hardware implementation of an MPPT controller because I wanted to make my application as reliable as possible and have more software resources for the home controller task.

One board provides power management and the other enables communication, which includes additional hardware such as an SD card, an XBee module, and an RTCC. Note: I included the RTCC since the chipKIT board does not come with a crystal oscillator. I also included a prototyping area, which later proved to be very useful.

I was concerned about how users inside a home would interact with the device. The idea of a built-in web server to help configure and interact with the device had not materialized before I submitted the contest entry. This solution is very practical, since you can access the device through its built-in server to configure or download log files while you are on your home network.

POWER MANAGEMENT BOARD
To make the system eco-friendly, I needed to enable continuous device operation using only a solar panel and a rechargeable Li-ion battery. The system consumes a considerable amount of power, so it needed a charge controller. Its main task was to control the battery-charging process. However, to work properly, it also had to account for the solar panel’s characteristics.

A solar panel can’t deliver constant power like a wall DC adapter does. Instead, power varies in a complex way according to atmospheric conditions (e.g., light and temperature).
For a given set of operational conditions, there is always a single operating point where the panel delivers its maximum power. The idea is to operate the panel in the maximum power point regardless of the external conditions.

I used Linear Technology’s LT3652 MPPT charger IC, which uses an input voltage regulation loop. The chip senses the panel output voltage and maintains it over a value by adjusting the current drawn. A voltage divider network is used to program the setpoint.
You must know the output voltage the panel produces when operated at the maximum power point. I couldn’t find the manufacturer’s specification sheet for the solar panel, but the distributor provides some experimental numbers. Because I was in a hurry to meet the contest deadline, I used that information. Based on those tests, the solar panel can produce approximately 8 V at 1.25 A, which is about 10 W of power.

I chose 8 V as the panel’s maximum power point voltage. The resistor divider output is connected to the LT3652’s VIN_REG pin. The chip has a 2.7-V reference, which means the charge current is reduced when this pin’s voltage goes below 2.7 V.

I used a two-cell Li-ion battery, but since the LTC3652 works with two, three, and four cells, the same board with different components can be used with a three- or four-cell battery. The LT3652 requires an I/O voltage difference of at least 3.3 V for reliable start-up, and it was clear that the panel’s 8-V nominal output would not be enough. I decided to include a voltage step-up stage in front of the LT3652.

I used Linear Technology’s LT3479 DC/DC converter to get the panel output to around 18 V to feed the MPPT controller. This only works if the LT3562’s voltage control loop still takes the VIN_REG reference directly from the panel output. Figures 1 and 2 show the circuit.

Power management board

Figure 1: Power management board

Figure 2: Power management board

Figure 2: Power management board

I could have fed the chipKIT on-board 5-V linear regulator with the battery, but I preferred to include another switching regulator to minimize losses. I used Linear Technology’s LTC3112 DC/DC converter. The only problem was that I needed to be able to combine its output with the chipKIT board’s 5 V, either through the USB port or the DC wall adapter option.

The chipKIT board includes a Microchip Technology MCP6001 op-amp in comparator configuration to compare USB voltage against a jack DC input voltage, enabling only one to be the 5-V source at a given time. Something similar was needed, so I included a Linear Technology LTC4411 IC, which is a low-loss replacement ORing diode, to solve the problem.

To my knowledge, when I designed the board a battery gauge for two-cell lithium batteries (e.g., a coulomb counter that can indicate accumulated battery charge and discharge) wasn’t available. The available options needed to handle most of the computational things in software, so I decided it was not an option. I included a voltage buffer op-amp to take advantage of the LTC3112’s dedicated analog voltage output, which gives you an estimate of the instantaneous current being drawn. Unfortunately, I wasn’t able to get it to work. So I ended up not using it.

Building this board was a challenge, since most components are 0.5-mm pitch with exposed pads underneath. IC manufacturers suggest using a solid inner ground layer for switching regulators, so I designed a four-layer board. If you have soldering experience, you can imagine how hard it is to solder the board using only a hot air gun and a soldering iron. That’s why I decided it was time to experiment with a stencil, solder paste, and a convection oven. I completed the board by using a commercially available kitchen convection oven and manually adjusting the temperature to match the reflow profile since I don’t have a controller (see Photo 2).

Photo 3: Custom chipSOLAR board

Photo 2: Custom chipSOLAR board

WIRELESS BOARD
The wireless board has all the components for GPRS communication and the 802.15.4 home network, as well as additional components for the SD file system and the RTCC. Figure 3 shows the circuit.

Figure 3: The communication board schematic is shown.

Figure 3: The communication board schematic is shown.

At the time of the contest, I used a SIMCom Wireless Solutions SIM340 GPRS modem. The company now offers a replacement, the SIM900B. The only physical differences are the board-to-board connectors, but the variations are so minimal that you can use the same footprint for both connectors.

During the contest, I only had the connector for the SIM340 on hand, so I based almost all the firmware on that model. Later, I got the SIM900B connector and modified the firmware. The Project Files include the #if defined clause for SIM900 or SIM340 snippets.

A couple of things made me want to test the SIM900B module, among them the Simple Mail Transfer Protocol (SMTP) server functionality and Multimedia Messaging Service (MMS). Ultimately, I discovered that my 32-MB flash memory version of the SIM900B was not suitable for those firmware versions. The 64-MB version of the hardware is required.
The subscriber identity module (SIM) card receptacle and associated ESD protection circuitry are located on the upper side of the board. The I/O lines connected to the modem are serial TX, RX, and a power-on signal using a transistor.

The chipKIT Max32 board does not have a 32,768-Hz crystal, so Microchip Technology’s PIC32 internal RTCC was not an option. I decided to include Microchip Technology’s MCP79402 RTCC with a super capacitor, mainly for service purposes as the system is already backed up with the lithium battery.

I should have placed the SD card slot on the top of the board. That could have saved me some time during the debugging stage, when I have had some problems with SD firmware that corrupts the SD file system. When I designed the board, I was trying to make it compatible with other platforms, so I included level translators for the SD card interface. I made the mistake of placing a level translator at the master input slave output (MISO), which caused a conflict in the bus with other SPI devices. I removed it and wire-wrapped the I/O lines.

Another issue with this board was the XBee module’s serial port net routing, but it was nothing that cutting some traces and wire wrap could not fix. Photo 3 shows all the aforementioned details and board component location.

Photo 3: This communication board includes several key components to enable wireless communication with sensors,  the Internet, and cellular networks.

Photo 3: This communication board includes several key components to enable wireless communication with sensors,the Internet, and cellular networks.

Editor’s Note: Visit here to read about other projects from the 2012 DesignSpark chipKIT Challenge.

Member Profile: Scott Weber

Scott Weber

Scott Weber

LOCATION:
Arlington, Texas, USA

MEMBER STATUS:
Scott said he started his Circuit Cellar subscription late in the last century. He chose the magazine because it had the right mix of MCU programming and electronics.

TECH INTERESTS:
He has always enjoyed mixing discrete electronic projects with MCUs. In the early 1980s, he built a MCU board based on an RCA CDP1802 with wirewrap and programmed it with eight switches and a load button.

Back in the 1990s, Scott purchased a Microchip Technology PICStart Plus. “I was thrilled at how powerful and comprehensive the chip and tools were compared to the i8085 and CDP1802 devices I tinkered with years before,” he said.

RECENT EMBEDDED TECH ACQUISITION:
Scott said he recently treated himself to a brand-new Fluke 77-IV multimeter.

CURRENT PROJECTS:
Scott is building devices that can communicate through USB to MS Windows programs. “I don’t have in mind any specific system to control, it is something to learn and have fun with,” he said. “This means learning not only an embedded USB software framework, but also Microsoft Windows device drivers.”

THOUGHTS ON THE FUTURE OF EMBEDDED TECH:
“Embedded devices are popping up everywhere—in places most people don’t even realize they are being used. It’s fun discovering where they are being applied. It is so much easier to change the microcode of an MCU or FPGA as the unit is coming off the assembly line than it is to rewire a complex circuit design,” Scott said.

“I also like Member Profile Joe Pfeiffer’s final comment in Circuit Cellar 276: Surface-mount and ASIC devices are making a ‘barrier to entry’ for the hobbyist. You can’t breadboard those things! I gotta learn a good way to make my own PCBs!”