DIY Internet-Enabled Home Control System

Why shell out hundreds or thousands of dollars on various home control systems (HCS) when you have the skills and resources to build your own? You can design and implement sophisticated Internet-enabled systems with free tools and some careful planning.

John Breitenbach did just that. He used a microcontroller, free software, and a cloud-based data platform to construct a remote monitoring system for his home’s water heater. The innovative design can email or text status messages and emergency alerts to a smartphone. You can build a similar system to monitor any number of appliances, rooms, or buildings.

An abridged version of Breitenbach’s article, “Internet-Enabled Home Control” (Circuit Cellar 264, July 2012), appears below. (A link to the entire article and an access password are noted at the end of this post.) Breitenbach writes:

Moving from the Northeast to North Carolina, my wife and I were surprised to find that most homes don’t have basements. In the north, the frost line is 36˝–48 ˝ below the surface. To prevent frost heave, foundations must be dug at least that deep. So, digging down an extra few feet to create a basement makes sense. Because the frost line is only 15 ˝ in the Raleigh area, builders rarely excavate the additional 8’ to create basements.

The lack of basements means builders must find unique locations for a home’s mechanical systems including the furnace, AC unit, and water heater. I was shocked to find that my home’s water heater is located in the attic, right above one of the bedrooms (see Photo 1).

Photo 1: My home’s water heater is located in our attic. (Photo courtesy of Michael Thomas)

During my high school summers I worked for my uncle’s plumbing business (“Breitenbach Plumbing—We’re the Best, Don’t Call the Rest”) and saw firsthand the damage water can do to a home. Water heaters can cause some dramatic end-of-life plumbing failures, dumping 40 or more gallons of water at once followed by the steady flow of the supply line.

Having cleaned up the mess of a failed water heater in my own basement up north, I haven’t had a good night’s sleep since I discovered the water heater in my North Carolina attic. For peace of mind, especially when traveling, I instrumented my attic so I could be notified immediately if water started to leak. My goal was to use a microcontroller so I could receive push notifications via e-mails or text messages. In addition to emergency messages, status messages sent on a regular basis reassure me the system is running. I also wanted to use a web browser to check the current status at any time.


The attic monitor is based on Renesas Electronics’s YRDKRX62N demonstration kit, which features the RX62N 32-bit microcontroller (see Photo 2). Renesas has given away thousands of these boards to promote the RX, and the boards are also widely available through distributors. The YRDK board has a rich feature set including a graphics display, push buttons, and an SD-card slot, plus Ethernet, USB, and serial ports. An Analog Devices ADT7420 digital I2C temperature sensor also enables you to keep an eye on the attic temperature. I plan to use this for a future addition to the project that compares this temperature to the outside air temperature to control an attic fan.

Photo 2: The completed board, which is based on a Renesas Electronics YRDKRX62N demonstration kit. (Photo courtesy of Michael Thomas)


Commercial water-detection sensors are typically made from two exposed conductive surfaces in close proximity to each other on a nonconductive surface. Think of a single-sided PCB with no solder mask and tinned traces (see Photo 3).

Photo 3: A leak sensor (Photo courtesy of Michael Thomas)

These sensors rely on the water conductivity to close the circuit between the two conductors. I chose a sensor based on this type of design for its low cost. But, once I received the sensors, I realized I could have saved myself a few bucks by making my own sensor from a couple of wires or a piece of proto-board.

When standing water on the sensor shorts the two contacts, the resistance across the sensor drops to between 400 kΩ and 600 kΩ. The sensor is used as the bottom resistor in a voltage divider with a 1-MΩ resistor up top. The output of the divider is routed to the 12-bit analog inputs on the RX62N microcontroller. Figure 1 shows the sensor interface circuit. When the voltage read by the analog-to-digital converter (ADC) drops below 2 V, it’s time to start bailing. Two sensors are connected: one in the catch pan under the water heater, and a second one just outside the catch pan to detect failures in the small expansion tank.

Figure 1: The sensor interface to the YRDK RX62N board


One of my project goals was to push notifications to my cell phone because Murphy’s Law says water heaters are likely to fail while you’re away for the weekend. Because I wanted to keep the project costs low, I used my home’s broadband connection as the gateway for the attic monitor. The Renesas RX62N microcontroller includes a 100-Mbps Ethernet controller, so I simply plugged in the cable to connect the board to my home network. The open-source µIP stack supplied by Renesas with the YRDK provides the protocol engine needed to talk to the Internet.

There were a couple of complications with using my home network as the attic monitor’s gateway to the world. It is behind a firewall built into my router and, for security reasons, I don’t want to open up ports to the outside world.

My Internet service provider (ISP) occasionally changes the Internet protocol (IP) address associated with my cable modem. So I would never know what address to point my web browser. I needed a solution that would address both of these problems. Enter Exosite, a company that provides solutions for cloud-based, machine-to-machine (M2M) communications.


Exosite provides a number of software components and services that enable M2M communications via the cloud. This is a different philosophy from supervisory control and data acquisition (SCADA) systems I’ve used in the past. The control systems I’ve worked on over the years typically involve a local host polling the hundreds or thousands of connected sensors and actuators that make up a commercial SCADA system. These systems are generally designed to be monitored locally at a single location. In the case of the attic monitor, my goal was to access a limited number of data points from anywhere, and have the system notify me rather than having to continuously poll. Ideally, I’d only hear from the device when there was a problem.

Exosite is the perfect solution: the company publishes a set of simple application programming interfaces (APIs) using standard web protocols that enable smart devices to push data to their servers in the cloud in real time. Once the data is in the cloud, events, alerts, and scripts can be created to do different things with the data—in my case, to send me an e-mail and SMS text alert if there is anything wrong with my water heater. Connected devices can share data with each other or pull data from public data sources, such as public weather stations. Exosite has an industrial-strength platform for large-scale commercial applications. It provides free access to it for the open-source community. I can create a free account that enables me to connect one or two devices to the Exosite platform.

Embedded devices using Exosite are responsible for pushing data to the server and pulling data from it. Devices use simple HTTP requests to accomplish this. This works great in my home setup because the attic monitor can work through my firewall, even when my Internet provider occasionally changes the IP address of my cable modem. Figure 2 shows the network diagram.

Figure 2: The cloud-based network


Web-based dashboards hosted on Exosite’s servers can be built and configured to show real-time and historical data from connected devices. Controls, such as switches, can be added to the dashboards to push data back down to the device, enabling remote control of embedded devices. Because the user interface is “in the cloud,” there is no need to store all the user interface (UI) widgets and data in the embedded device, which greatly reduces the storage requirements. Photo 4 shows the dashboard for the attic monitor.

Photo 4: Exosite dashboard for the attic monitor

Events and alerts can be added to the dashboard. These are logical evaluations Exosite’s server performs on the incoming data. Events can be triggered based on simple comparisons (e.g., a data value is too high or too low) or complex combinations of a comparison plus a duration (e.g., a data value remains too high for a period of time). Setting up a leak event for one of the sensors is shown in Photo 5.

Photo 5: Creating an event in Exosite

In this case, the event is triggered when the reported ADC voltage is less than 2 V. An event can also be triggered if Exosite doesn’t receive an update from the device for a set period of time. This last feature can be used as a watchdog to ensure the device is still working.

When an event is triggered, an alert can optionally be sent via e-mail. This is the final link that enables an embedded device in my attic to contact me anywhere, anytime, to alert me to a problem. Though I have a smartphone that enables me to access my e-mail account, I can also route the alarm message to my wife’s simpler phone through her cellular provider’s e-mail-to-text-message gateway. Most cellular providers offer this service, which works by sending an e-mail to a special address containing the cell phone number. On the Verizon network, the e-mail address is <yourcellularnumber> Other providers have similar gateways.

The attic monitor periodically sends heartbeat messages to Exosite to let me know it’s still working. It also sends the status of the water sensors and the current temperature in the attic. I can log in to Exosite at any time to see my attic’s real-time status. I have also configured events and alarms that will notify me if a leak is detected or if the temperature gets too hot…

The complete article includes details such about the Internet engine, reading the cloud, tips for updating the design, and more.  You can read the entire article by typing netenabledcontrol to open the password-protected PDF.

The Renesas RL78 for Low-Power Applications

Renesas Technology announced in late March he start of a design challenge for engineers around the world: develop an innovative, low-power application using the RL78 MCU and IAR Systems toolchain. To get started, you need to familiarize yourself with the RL78. Clemens Valens, Editor-in-Chief of Elektor online, introduces the RL78 in a comprehensive “The RL78 Microcontroller: An MCU Family for Low-Power Applications” (Circuit Cellar 261, 2012).

I’ve worked with Valens in various occasions, and had the pleasure of meeting him in 2011. He’s truly “an engineer’s engineer”: extremely embedded tech savvy, well-read, and inquisitive. Furthermore, I edited Circuit Cellar articles Valens wrote about diverse design projects, such as a virtual instrument interface and a scrolling LED message board. Thus, it’s clear to me that Valens understands the importance of designing high-quality, energy-efficient, systems—and doing so within budget. I trust you’ll find his introduction to the RL78 insightful and immediately applicable.

The RL78 Microcontroller: An MCU Family for Low-Power Applications

By Clemens Valens (Circuit Cellar 261, 2012)

The low-power 8/16-bit microcontroller (MCU) market is a bit of a warzone with several MCU manufacturers proposing “the industry’s lowest power solution.” In a YouTube video, Texas Instruments boasts a best active figure of 160 μA/MIPS for their MSP430 family. In application note AN1267, Microchip Technology claims 110 μA at “1 MHz Run” for their PIC16LF72X. And Renesas Electronics announced 70 μA at “1-MHz normal operation” on their RL78 product website.[1, 2, 3] The absence of justification on how exactly these figures were obtained makes comparing them rather useless. But then again, you don’t really have to because, as most low-power developers know from experience, if you don’t get the hardware and software design right, you will never attain the promised 20-year battery lifetime no matter how low the MCU’s active, sleep, or standby current may be. In this article, I will take a closer look at Renesas’s quickly expanding RL78 family to see what they offer that may help you create a low-power design.

Photo 1 - The Renesas RL78


The RL78 family of 16-bit MCUs currently has two branches, “generic” and “application specific,” but a third “display” branch is forthcoming. The generic branch contains the subfamilies G12, G13, and G1A, all based on the 78K core, and the G14, which is based on the R8C core. In the application-specific branch there is the 1A and F12. I am not sure about their core origins as these products are still very new and, at the time of writing, documentation is missing. It doesn’t really matter; from now on it is the new RL78 core for all. Since they share the same core, I will concentrate on the G13 for which I have a nice evaluation board (see Photo 1 and “The Renesas Demonstration Kit for RL78” sidebar).

Sidebar: Renesas Demonstration Kit


This family comes in a large number of variants (I counted 182), with devices having from 20 up to 128 pins (see Figure 1). Note that the parts themselves are labelled R5F10xx. The differences between all these variants are, besides the package type, the amounts of flash memory (program and data) and RAM. Program flash memory starts at 16 KB and currently ends at 512 KB, data flash sizes can be 0, 4, or 8 KB and RAM is 2 KB for the small devices and up to 32 KB for the big ones.

Figure 1 - Diagram of 128-pin RL78/G13 devices

The CPU is 16-bit, but the internal memory architecture is 8 bit. Its 32 general-purpose registers are organized in four banks of eight and can be used as 8- or 16-bit registers. The memory-mapped special function registers (SFRs) that control the on-chip peripherals can be addressed per bit, per byte, or as 16-bit registers, depending on the register. A second set of SFRs, the extended or second SFRs, are available too, but they need longer instructions to be accessed.

For those who need to squeeze the maximum out of MCU performance, it may be interesting to know that the CPU offers a short addressing mode enabling you to access a page of 256 bytes with a minimum amount of code.

The maximum clock frequency of the processor is 32 MHz, but the hardware user’s manual, which is almost 1,100 pages, interestingly also boasts about the ultra-low-speed capabilities of the processor as it can run from a 32.768-kHz clock.

The RL78 core features 15 I/O ports, most of which are 8-bit wide. Port 13 is 2-bit wide and ports 10 and 15 are 7-bit wide. The port pins that are actually available depend on the device. Inputs and outputs are highly configurable. Inputs can be analog, CMOS, or TTL. Outputs can be CMOS or N-channel open drain. Pull-up resistors are available too. The exact configuration possibilities depend on the port pin, so consult the datasheet. Because of the many configuration options, it is possible to use the MCU in multi-voltage systems without level-shifting circuitry except for the occasional external pull-up resistor. The chip can be powered from 1.6 V to 5.5 V, the core itself runs from 1.8 V provided by an internal voltage regulator.


Several options are available for the MCU clock. When clock precision is not too important, the MCU can be run from its internal clock, up to 32 MHz, otherwise it is possible to connect an external crystal, resonator, or oscillator. An internal low-speed clock (15 kHz) is also available, but not for the CPU, only for the watchdog timer (WDT), the real-time clock (RTC), and the interval timer.

The timers of the RL78 are flexible and offer many functions. Depending on the pin size of the device, you can have up to 16 16-bit timers, grouped in two arrays of eight. Each timer (called a “channel”) can function as an interval timer, square-wave generator, event counter, frequency divider, pulse-interval timer, pulse-duration timer, and delay counter. For even more possibilities, timers can be combined to create monostable multivibrators or to do pulse-width modulation (PWM). This way, up to seven PWM signals can be generated from one master timer. If you need more timers but resolution is less important, you can split some 16-bit timers in two 8-bit timers (this is not possible with all timers). Timer 7 of array 0 is extra special as it features local interconnect network (LIN) network support (see below).

Aside from date and time keeping with alarms, the RTC also provides constant period interrupts at 2 Hz and 1 Hz and also every minute, hour, day, or month. A 1-Hz output is available on devices with 40 or more pins. For extra precision, the RTC offers a correction register for fine tuning the 32,768-kHz clock. Unsurprisingly, the RTC continues operation when the MCU is stopped.

Now that I mentioned Stop mode, a special interval timer peripheral enables wakeup from this mode at periodic intervals. This timer is also used for the analog-to-digital converter’s (ADC’s) Snooze mode. More on that later. With a clock frequency of 32,768 Hz, the lowest interval rate is 8 Hz (0.125 ms).

Yet another time-related peripheral on the RL78 is the buzzer controller (not available on 20-pin devices). This is a clock output destined at IR comms carrier generation, to clock other chips in a system or to produce sound from a buzzer. A gate bit enables modulation of this output in such a way that pulses always have the same width.

Finally, a WDT completes the timing peripherals. It has a special Window mode that limits the time frame during which you can reset the watchdog to a fraction of the watchdog interval (50%, 75%, or 100%). Resetting the watchdog counter outside the window results in a reset. The window is open in the second part of the interval. An interrupt can be generated when the WDT reaches 75% of its time-out value, (i.e., when the watchdog reset window is known to be open in all cases). Figure 2 illustrates the mechanism.

Figure 2 - Trying to reset the watchdog counter when the window is closed results in an internal reset signal


The ADC is of the 10-bit successive approximation type and can have up to 26 inputs. Several triggering options are provided, hardware and software, where hardware triggering means triggering by a timer module (timer channel 1 end of count or capture, interval timer, or RTC). The time it takes to do a conversion depends partly on the triggering mode. When input stabilization is not too much of an issue (i.e., when you don’t switch inputs) you can achieve conversion times of just over 2 μs.

Two registers enable comparing the ADC’s output to maximum and minimum values, producing an interrupt when the new value is either in or out of bounds. This function is also available in Snooze mode. In this mode, the processor itself is stopped and consumes very little power, but ADC conversions continue under control of the hardware trigger. When a conversion triggers an ADC interrupt, the processor can then wake up from Snooze mode and resume normal operation.


The RL78 features multifunction serial units. The devices with 25 pins or less have one such unit, the others have two. Only serial unit 2 provides LIN bus support.

A serial unit can function in asynchronous UART mode, in synchronous CSI mode (three-wire bus with clock, data in and data out signals, master and slave mode supported), and in simplified (master-only) I²C mode. Again, depending on the device, you can have up to four UARTs or eight CSI and/or simplified I²C ports. Of course a mix is also possible. Full I²C is possible with the specialized I²C unit.

UART0 and UART2, CSI00 and CSI20 provide Snooze mode functionality similar to the ADC. In Snooze mode, these ports can be made to wake up on the arrival of incoming data without waking up the CPU. If the received data is interesting enough, it is also possible to wake up the CPU.

LIN communications are possible with UART2 together with Timer 7 of Array 0. The LIN bus is an inexpensive alternative to the CAN bus in automotive systems to control simple devices like switches, sensors, and actuators. LIN only uses one wire and is rather low speed (20 Kbps maximum). The timer takes care of the LIN synchronization issues and the UART performs the (de)serialisation of the data.

Full blown I²C communication is possible with the specialized I²C peripheral IICA. The 80-pin and more devices have two channels, the others only one. Communication speeds up to 20 MHz are permitted to enable I²C “fast mode” (3.5 MHz) and “fast mode plus” (10 MHz). This module is capable of waking up the CPU from Stop mode.


Of interest is the hardware multiplier and divider module intended for filtering and FFT functions. This module is capable of 16 × 16 bits signed and unsigned multiplications and divisions producing 32-bit results. It can also do 16 × 16 bit multiply-accumulate. We are talking about a module here, not an instruction, meaning that you have to load the operands yourself in special registers and get the result from yet another. The multiplication itself is done in one clock cycle, a division takes 16. The accumulate operation adds another cycle.

Another special math function is the binary-coded decimals (BCD) correction register that enables you to easily transform binary calculation results into BCD results.


To speed up data transport without loading the CPU, the RL78 core features direct memory access (DMA), up to four channels. DMA transfers up to 1,024 words of data (8 or 16 bit) to and from SFRs and RAM and they can be started by a range of interrupts (e.g., ADC, serial, timer). Although DMA transfers are done in parallel with normal CPU operation, it does slow down the CPU. For time-critical situations, it is possible to put a DMA transfer on hold for a number of clock cycles and let the CPU finish its job first.


Interrupts are pretty standard on the RL78 and many sources are available. The “key interrupt” function on the other hand is less common. It provides up to eight (depending on the device, you guessed it) key or push button inputs that are ORed together to generate an interrupt on a key press (active low).


Besides the aforementioned Stop and Snooze modes, the RL78 also provides a Halt mode. In this mode, the CPU is stopped but the clocks keep running, making a fast resume possible. In Stop mode, the clocks are stopped too reducing power consumption more than in Halt mode. Snooze mode is like Stop mode, but with one or more peripherals in a snoozing state, ready to wake up when something interesting happens. Interrupts can be used to wake up from Snooze, Stop, or Halt mode. A reset usually works too.

Reset, by the way, can have seven origins, three of which are related to safety functions: illegal instruction, RAM parity, and illegal memory access. Two others involve the power supply: power-on reset (POR) and low-voltage detection (LVD). All these reset options are needed to conform to the International Electrotechnical Commission (IEC) 60730-1 (“Automatic Electrical Controls for Household and Similar Use; Part 1: General Requirements”) and IEC 61508-SER (“Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems”) safety standards. Since the RL78 is compliant, it also implements flash memory CRC checking, protections to prevent RAM and SFRs to be modified when the CPU stops functioning, an oscillator frequency-detection circuit, and an ADC self-test function.

The hardware used for the flash memory CRC check is also available as a general-purpose CRC module for user programs. It implements the standard CCITT CRC-16 polynomial (X^16 + X^12 + X^5 + 1).

The RAM guard function protects only up to 512 bytes, so be careful where you put your sensitive data.


Those familiar with the fuse bytes of PIC and AVR processors will be happy to know that the RL78 contains four of them, the option bytes that configure such things as the WDT, low-voltage detection, flash memory modes, clock frequencies, and debugging modes.

Flash memory is divided into two parts, program memory and data memory, and it can be programmed in-circuit over a serial interface. A boot partition is available too. This partition uses a kind of ping-pong mechanism called “boot swapping” to ensure that a valid bootloader is always programmed into the boot partition so that even power failures during bootloader programming will not harm the boot partition. A flash window function protects the memory against unintentionally reprogramming parts of it.


This concludes our voyage through the Renesas RL78 core. As you have seen, the RL78 offers many interesting peripherals all combined in a flexible low-power optimized design. Thanks to the integrated oscillator and other functions, an RL78 MCU can be used with very little external hardware, enabling inexpensive and compact designs. Once you master its Snooze mode and your low-power design skills, you can use this MCU family in battery-operated metering applications, for instance, but I am sure you can think of something more surprising.

Clemens Valens ( is Editor-in-Chief of Elektor Online. He has more than 15 years of experience in embedded systems design. Clemens is currently interested in sound synthesis techniques, rapid prototyping, and the popularization of technology.


[1] Texas Instruments, Inc., “Ultra-Low Power MSP430 – The World’s Lowest Power MCU,” 201.

[2] Microchip Technology, Inc., “AN1267: nanoWatt and nanoWatt XLP Technologies: An Introduction to Microchip’s Low-Power Devices,” 2009.

[3] Renesas Electronics Corp., “RL78 Family,”


International Electrotechnical Commission (IEC), “60730-1, Automatic Electrical Controls for Household and Similar Use; Part 1: General Requirements,” 2002.

———, “61508-SER, Functional Safety of Electrical/

Electronic/Programmable Electronic Safety-Related Systems,” 2010.

Renesas Electronics Corp., Renesas Rulz, “RL78/G13 Demonstration Kit,”

For more information about the RL78 Family of microcontrollers, visit

For information about the 2012 Renesas RL78 Green Energy Challenge (in association with Elektor & Circuit Cellar), go to

This article appears in Circuit Cellar 261 (April 2012).



Tech Highlights from Design West: RL78, AndroPod, Stellaris, mbed, & more

The Embedded Systems Conference has always been a top venue for studying, discussing, and handling the embedded industry’s newest leading-edge technologies. This year in San Jose, CA, I walked the floor looking for the tech Circuit Cellar and Elektor members would love to get their hands on and implement in novel projects. Here I review some of the hundreds of interesting products and systems at Design West 2012.


Renesas launched the RL78 Design Challenge at Design West. The following novel RL78 applications were particularly intriguing.

  • An RL78 L12 MCU powered by a lemon:

    A lemon powers the RL78 (Photo: Circuit Cellar)

  • An RL78 kit used for motor control:

    The RL78 used for motor control (Photo: Circuit Cellar)

  • An RL78 demo for home control applications:

    The RL78 used for home control (Photo: Circuit Cellar)


Circuit Cellar members have used TI products in countless applications. Below are two interesting TI Cortex-based designs

A Cortex-M3 digital guitar (you can see the Android connection):

TI's digital guitar (Photo: Circuit Cellar)

Stellaris fans will be happy to see the Stellaris ARM Cortex -M4F in a small wireless application:

The Stellaris goes wireless (Photo: Circuit Cellar)

NXP mbed

Due to the success of the recent NXP mbed Design Challenge, I stopped at the mbed station to see what exciting technologies our NXP friends were exhibiting. They didn’t disappoint. Check out the mbed-based slingshot developed for playing Angry Birds!

mbed-Based sligshot for going after "Angry Birds" (Photo: Circuit Cellar)

Below is a video of the project on the mbedmicro YouTube page:


I was pleased to see the Elektor AndroPod hard at work at the FTDI booth. The design enables users to easily control a robotic arm with Android smartphones and tablets.

FTDI demonstrates robot control with Android (Photo: Circuit Cellar)

As you can imagine, the possible applications are endless.

The AndroPod at work! (Photo: Circuit Cellar)

Renesas RL78 Green Energy Challenge

Up for an international design challenge? It’s time for the Renesas RL78 Green Energy Challenge! Renesas has partnered with IAR Systems to deliver engineers a power-house combo of low-power devices and high-quality software. They’re steering a great, green revolution and are challenging you to transform how the world experiences energy efficiency by developing a unique, low-power application using the RL78 MCU and IAR toolchain. Succeed and win a share of $17,500 in Grand Prizes from Renesas! * The Renesas Grand Prize winner will also win a free trip to Renesas DevCon in October where winners will be announced.

But that’s not all. Earn additional prizes like developments tools, Pmods, Wi-Fi modules, embedded systems books, and more from Contest Partners through weekly prize drawings. Follow Renesas on Twitter and Facebook for weekly challenge questions from official Contest Partners. Weekly Partner Challenges, and the respective winners, will be announced every Monday throughout the competition.

So, do you have a great idea for a remote device that monitors pollution? What about a box collecting data on home power usage or an energy harvesting biometric design? Perhaps your grand plan is for a low power controller scavenging heat from an oven or furnace, a meter reading biomass parameters, or a braking system for a wind turbine? It’s up to you! Send us your best RL78 based ideas to help make the world a better place.

The Challenge starts March 26, 2012 and ends on August 31, 2012. Winners will be announced in October at Renesas’ DevCon 2012.

Hundreds of free RL78/G13 development kits (“RDK”s), loaded with IAR’s Kickstart edition, are being distributed to those who qualify. Click here to see if you qualify for a complimentary RDK!

*Prizes in U.S. dollars.

Circuit Cellar, Inc. and Elektor International Media is the Contest Administrator.


Issue 261: Renesas RL78, Cap Touch, Synapse SNAP, & More!

Here’s a sneak peek at the projects and topics slated for the April issue of Circuit Cellar: Linux software development tools, DIY cap-touch, gain-controlled amplifier; color classification reader; start designing with the Renesas RL78 microcontroller; an introduction to sigma-delta modulators; RFI bypassing, with a focus on parallel capacitors; mesh networking simplified with SNAP technology; and more.


Clemens Valens introduces the Renesas Electronics RL78:

Click the image to link to the Renesas product page

Jeff Bachiochi takes a close look at Synapse Wireless SNAP technology:

Click the image to link to the Synapse-Wireless Kit webpage

Ed Nisley presents Part 2 of his article series “RFI Bypassing”:

The tracking generator output and spectrum analyzer input connect to adjacent PCB pads on the left of the SMD capacitor. Connecting the spectrum analyzer to the pad on the right side changes the measured self-resonant frequency.

The April issue will hit newsstands in late March.