Doing the Robot, 21st-Century Style

Growing up in the 1970s, the first robot I remember was Rosie from The Jetsons. In the 1980s, I discovered Transformers, which were touted as “robots in disguise,” I imitated Michael Jackson’s version of “the robot,” and (unbeknownst to me) the Arthrobot surgical robot was first developed. This was years before Honda debuted ASIMO, the first humanoid robot, in 2004.

“In the 1970s, microprocessors gave me hope that real robots would eventually become part of our future,” RobotBASIC codeveloper John Blankenship told me in a 2013 interview. It appears that the “future” may already be here.

Honda's ASIMO humanoid robot

Honda’s ASIMO humanoid robot

Welcome to the 21st century. Technology is becoming “smarter,“ as evidenced at the Consumer Electronics Show (CES) 2014, which took place in January. The show unveiled a variety of smartphone-controlled robots and drones as well as wireless tracking devices.

Circuit Cellar’s columnists and contributors have been busy with their own developments. Steve Lubbers wondered if robots could be programmed to influence each other’s behavior. He used Texas Instruments’s LaunchPad hardware and a low-cost radio link to build a group of robots to test his theory. The results are on p. 18.

RobotBASIC’s Blankenship wanted to program robots more quickly. His article explains how he uses robot simulation to decrease development time (p. 30).

The Internet of Things (IoT), which relies on embedded technology for communication, is also making advancements. According to information technology research and advisory company Gartner, by 2020, there will be close to 26 billion devices on the IoT.

With the IoT, nothing is out of the realm of a designer’s imagination. For instance, if you’re not at home, you can use IoT-based platforms (such as the one columnist Jeff Bachiochi writes about on p. 58) to preheat your oven or turn off your sprinklers when it starts to rain.

Meanwhile, I will program my crockpot and try to explain to my 8-year-old how I survived childhood without the Internet.

Arduino MOSFET-Based Power Switch

Circuit Cellar columnist Ed Nisley has used Arduino SBCs in many projects over the years. He has found them perfect for one-off designs and prototypes, since the board’s all-in-one layout includes a micrcontroller with USB connectivity, simple connectors, and a power regulator.

But the standard Arduino presents some design limitations.

“The on-board regulator can be either a blessing or a curse, depending on the application. Although the board will run from an unregulated supply and you can power additional circuitry from the regulator, the minute PCB heatsink drastically limits the available current,” Nisley says. “Worse, putting the microcontroller into one of its sleep modes doesn’t shut off the rest of the Arduino PCB or your added circuits, so a standard Arduino board isn’t suitable for battery-powered applications.”

In Circuit Cellar’s January issue, Nisley presents a MOSFET-based power switch that addresses such concerns. He also refers to one of his own projects where it would be helpful.

“The low-resistance Hall effect current sensor that I described in my November 2013 column should be useful in a bright bicycle taillight, but only if there’s a way to turn everything off after the ride without flipping a mechanical switch…,” Nisley says. “Of course, I could build a custom microcontroller circuit, but it’s much easier to drop an Arduino Pro Mini board atop the more interesting analog circuitry.”

Nisley’s January article describes “a simple MOSFET-based power switch that turns on with a push button and turns off under program control: the Arduino can shut itself off and reduce the battery drain to nearly zero.”

Readers should find the article’s information and circuitry design helpful in other applications requiring automatic shutoff, “even if they’re not running from battery power,” Nisley says.

Figure 1: This SPICE simulation models a power p-MOSFET with a logic-level gate controlling the current from the battery to C1 and R2, which simulate a 500-mA load that is far below Q2’s rating. S1, a voltage-controlled switch, mimics an ordinary push button. Q1 isolates the Arduino digital output pin from the raw battery voltage.

Figure 1: This SPICE simulation models a power p-MOSFET with a logic-level gate controlling the current from the battery to C1 and R2, which simulate a 500-mA load that is far below Q2’s rating. S1, a voltage-controlled switch, mimics an ordinary push button. Q1 isolates the Arduino digital output pin from the raw battery voltage.

The article takes readers from SPICE modeling of the circuitry (see Figure 1) through developing a schematic and building a hardware prototype.

“The PCB in Photo 1 combines the p-MOSFET power switch from Figure 2 with a Hall effect current sensor, a pair of PWM-controlled n-MOFSETs, and an Arduino Pro Mini into

The power switch components occupy the upper left corner of the PCB, with the Hall effect current sensor near the middle and the Arduino Pro Mini board to the upper right. The 3-D printed red frame stiffens the circuit board during construction.

Photo 1: The power switch components occupy the upper left corner of the PCB, with the Hall effect current sensor near the middle and the Arduino Pro Mini board to the upper right. The 3-D printed red frame stiffens the circuit board during construction.

a brassboard layout,” Nisley says. “It’s one step beyond the breadboard hairball I showed in my article “Low-Loss Hall Effect Current Sensing” (Circuit Cellar 280, 2013), and will help verify that all the components operate properly on a real circuit board with a good layout.”

For much more detail about the verification process, PCB design, Arduino interface, and more, download the January issue.

The actual circuit schematic includes the same parts as the SPICE schematic, plus the assortment of connectors and jumpers required to actually build the PCB shown in Photo 1.

Figure 2: The actual circuit schematic includes the same parts as the SPICE schematic, as well as the assortment of connectors and jumpers required to actually build the PCB shown in Photo 1.