Places for the IoT Inside Your Home

It’s estimated that by the year 2020, more than 30 billion devices worldwide will be wirelessly connected to the IoT. While the IoT has massive implications for government and industry, individual electronics DIYers have long recognized how projects that enable wireless communication between everyday devices can solve or avert big problems for homeowners.

February CoverOur February issue focusing on Wireless Communications features two such projects, including  Raul Alvarez Torrico’s Home Energy Gateway, which enables users to remotely monitor energy consumption and control household devices (e.g., lights and appliances).

A Digilent chipKIT Max32-based embedded gateway/web server communicates with a single smart power meter and several smart plugs in a home area wireless network. ”The user sees a web interface containing the controls to turn on/off the smart plugs and sees the monitored power consumption data that comes from the smart meter in real time,” Torrico says.

While energy use is one common priority for homeowners, another is protecting property from hidden dangers such as undetected water leaks. Devlin Gualtieri wanted a water alarm system that could integrate several wireless units signaling a single receiver. But he didn’t want to buy one designed to work with expensive home alarm systems charging monthly fees.

In this issue, Gualtieri writes about his wireless water alarm network, which has simple hardware including a Microchip Technology PIC12F675 microcontroller and water conductance sensors (i.e., interdigital electrodes) made out of copper wire wrapped around perforated board.

It’s an inexpensive and efficient approach that can be expanded. “Multiple interdigital sensors can be wired in parallel at a single alarm,” Gualtieri says. A single alarm unit can monitor multiple water sources (e.g., a hot water tank, a clothes washer, and a home heating system boiler).

Also in this issue, columnist George Novacek begins a series on wireless data links. His first article addresses the basic principles of radio communications that can be used in control systems.

Other issue highlights include advice on extending flash memory life; using C language in FPGA design; detecting capacitor dielectric absorption; a Georgia Tech researcher’s essay on the future of inkjet-printed circuitry; and an overview of the hackerspaces and enterprising designs represented at the World Maker Faire in New York.

Editor’s Note: Circuit Cellar‘s February issue will be available online in mid-to-late January for download by members or single-issue purchase by web shop visitors.

Workspace for Coding and Control System Development

Not every engineer’s workspace includes a recliner and a Chihuahua—but this setup works for David Cass Tyler, a retired embedded systems engineer from Willard, NM. Tyler’s “work environment” enables him to “do things at his own pace.”


“This is my normal working environment,” Tyler said. “My assistant is a 3-year-old Chihuahua that believes he is essential for me to correctly code.”

Tyler explained his work setup via e-mail:

When I require extra space to spread out, I move into the spare bedroom and use the desk in there to set up the hardware.

Almost all of my projects are developed to be distributed and accessible through the network. When I need to program on a different computer, I tend to use the remote desktop to program on other Windows-based systems. There is seldom a time when I have to physically move to one of the other systems, so this keeps my dog happy.


Tyler’s 256 I/O channel hardware simulator is shown. “This 24-VDC system has enough channels to comfortably simulate the hardware of almost any of my projects,” he explained.

Tyler is currently working on a 256 I/O channel hardware simulator. He says the PC/104 hardware stack gives him 256 channels of I/O, including 64 analog inputs, 24 analog outputs, and 168 digital I/Os, all in a single compact stack.

He provided some background detail about the system:

In 1995, I was a supervisor with ATK. I designed and had my crew build this system to provide hardware inputs to a control system we were developing for a government customer. I personally programmed the base system and others in my crew used it to develop the hardware simulator.

We also had a 3U 19” rack-mounted box that contained six Rabbit Semiconductor BL2100s, which were the actual controllers used in the system. They enabled us to build the control system before the actual hardware being controlled was delivered. This was the only time in my 30-plus year career that the system was delivered, the controllers were hooked up, and the system ran right out of the box. Of course we had some tweaking and tuning to do, but the system came up under control. There were subsystems that were potentially dangerous to human life, but, with the controllers in place, we were able to safely start up without hurting anyone and without breaking expensive custom equipment.

CassTylerBottom of Canister

The system connectors to Tyler’s 256-channel hardware system are shown.

Tyler also listed some advantages to using the system:

  • You can build the control system without having possession of the actual system.
  • During code coverage and fault testing, you can simulate faults that would be expensive or dangerous to test otherwise.
  • You can continue to develop components after the actual system has been delivered.
  • When writing the simulator, you can understand the interactions better and more completely.
  • You can do virtually all of the training on the simulator, using the exact actual software that will be delivered to the customer.
  • You can respond to many customer requests without having be present at the customer’s site.
CassTyler1553 Box

Tyler’s 1553 system

Tyler’s “workspace” includes several development systems from Rabbit Semiconductor and NetBurner as well as Microchip Technology PIC microcontrollers. He also has a MIL-STD-1553 system with a bus controller and a remote terminal, both controlled by Advantech PCM-3350 CPUs.

Tyler described some of his projects by saying:

I use a combination of hardware and software simulation to develop my control systems. Using hardware simulation, you can feed expected values to controllers to calibrate them and check their functionality. Using software-only functionality, you can develop systems anywhere. With virtual computers, you can test control systems distributed between multiple “computers.” Using this technique, you can deliver control systems, ready for final debugging, at the same time the system hardware is delivered—all from the comfort of your easy chair.

He provided a final thought about built-in web servers:

You can now embed web servers that enable you to run your system without installing anything on the user’s system. With ample available storage, you can put all the datasheets, manuals, and data files directly on the embedded controllers so they are always available, even without an Internet connection. Usually, you can also put some degree of manual control on the web server so you can perform at least rudimentary diagnostics and control.

Tyler is the owner and author of The Control Freak, which he uses to share back to the community. His is currently working on a Standard Commands for Programmable Instruments (SCPI) parser.

Tyler recently wrote a two-part article about Calibration. Part 1 will appear in Circuit Cellar’s November issue.