On the surface, a programmable logic controller (PLC) might seem like nothing more than a generic microcontroller, perhaps outfitted to operate in industrial settings with things like high temperatures or harsh vibrations. While this is true to some extent, PLCs also have an international standard for their architecture and programming languages. This standard is maintained by the International Electrotechnical Commission, making it so that any device built under these specifications will be recognizable to control engineers and maintenance personnel worldwide. And, if you use this standard when working with certain Arduinos, this common platform can become a standard-compliant PLC as well.

The IDE itself supports programming ladder diagrams, functional block diagrams, and other programming systems covered under the IEC 61131-3 standard. Not only that, it allows the combination of these types of PLC programming with Arduino sketches. The system offers many of the perks of PLC programming alongside the familiar Arduino platform, and supports a number of protocols as well including CANOpen, Modbus RTU, and Modbus TCP. It can also be used for monitoring a PLC system, essentially adding IoT capabilities to existing systems, enabling continuous monitoring, debugging, and program updates.

While not every Arduino is a great platform to build a PLC around, there are a few available for those looking for a system a little less proprietary and a little more user-friendly than typical PLC systems tend to be. There’s a reason that PLCs are built around an international standard and generally have certain hardware in mind to run it, though, and this comparison of a Raspberry Pi with an off-the-shelf PLC goes into detail about why certain components aren’t good choices for PLCs.

Gosh, what a shame: it turns out that perhaps 2 billion phones won’t be capable of COVID-19 contact-tracing using the API that Google and Apple are jointly developing. The problem is that the scheme the two tech giants have concocted, which Elliot Williams expertly dissected recently, is based on Bluetooth LE. If a phone lacks a BLE chipset, then it won’t work with apps built on the contact-tracing API, which uses the limited range of BLE signals as a proxy for the physical proximity of any two people. If a user is reported to be COVID-19 positive, all the people whose BLE beacons were received by the infected user’s phone within a defined time period can be anonymously notified of their contact. As Elliot points out, numerous questions loom around this scheme, not least of which is privacy, but for now, something like a third of phones in mature smartphone markets won’t be able to participate, and perhaps two-thirds of the phones in developing markets are not compatible. For those who don’t like the privacy-threatening aspects of this scheme, pulling an old phone out and dusting it off might not be a bad idea.

We occasionally cover stories where engineers in industrial settings use an Arduino for a quick-and-dirty automation solution. This is uniformly met with much teeth-gnashing and hair-rending in the comments asserting that Arduinos are not appropriate for industrial use. Whether true or not, such comments miss the point that the Arduino solution is usually a stop-gap or proof-of-concept deal. But now the purists and pedants can relax, because Automation Direct is offering Arduino-compatible, industrial-grade programmable controllers. Their ProductivityOpen line is compatible with the Arduino IDE while having industrial certifications and hardening against harsh conditions, with a rich line of shields available to piece together complete automation controllers. For the home-gamer, an Arduino in an enclosure that can withstand harsh conditions and only cost $49 might fill a niche.

Speaking of Arduinos and Arduino accessories, better watch out if you’ve got any modules and you come under the scrutiny of an authoritarian regime, because you could be accused of being a bomb maker. Police in Hong Kong allegedly arrested a 20-year-old student and posted a picture of parts he used to manufacture a “remote detonated bomb”. The BOM for the bomb was strangely devoid of anything with wireless capabilities or, you know, actual explosives, and instead looks pretty much like the stuff found on any of our workbenches or junk bins. Pretty scary stuff.

If you’ve run through every binge-worthy series on Netflix and are looking for a bit of space-nerd entertainment, have we got one for you. Scott Manley has a new video that goes into detail on the four different computers used for each Apollo mission. We knew about the Apollo Guidance Computers that guided the Command Module and the Lunar Module, and the Launch Vehicle Digital Computer that got the whole stack into orbit and on the way to the Moon, but we’d never heard of the Abort Guidance System, a backup to the Lunar Module AGC intended to get the astronauts back into lunar orbit in the event of an emergency. And we’d also never heard that there wasn’t a common architecture for these machines, to the point where each had its own word length. The bit about infighting between MIT and IBM was entertaining too.

And finally, if you still find yourself with time on your hands, why not try your hand at pen-testing a military satellite in orbit? That’s the offer on the table to hackers from the US Air Force, proprietor of some of the tippy-toppest secret hardware in orbit. The Hack-A-Sat Space Security Challenge is aimed at exposing weaknesses that have been inadvertantly baked into space hardware during decades of closed development and secrecy, vulnerabilities that may pose risks to billions of dollars worth of irreplaceable assets. The qualification round requires teams to hack a grounded test satellite before moving on to attacking an orbiting platform during DEFCON in August, with prizes going to the winning teams. Get paid to hack government assets and not get arrested? Maybe 2020 isn’t so bad after all.

When teaching Industrial Automation to students, you need to give them access to the things they will encounter in industry. Most subjects can be taught using computer programs or simulators — for example topics covering PLC, DCS, SCADA or HMI. But to teach many other concepts, you  need to have the actual hardware on hand to be able to understand the basics. For example, machine vision, conveyor belts, motor speed control, safety and interlock systems, sensors and peripherals all interface with the mentioned control systems and can be better understood by having hardware to play with. The team at [Absolutelyautomation] have published several projects that aim to help with this. One of these is the DIY conveyor belt with a motor speed control and display.

This is more of an initial, proof of concept project, and there is a lot of room for improvement. The build itself is straightforward. All the parts are standard, off the shelf items — stuff you can find in any store selling 3D printer parts. A few simple tools is all that’s required to put it together. The only tricky part of the build would likely be the conveyor belt itself. [Absolutelyautomation] offers a few suggestions, mentioning old car or truck tyres and elastic resistance bands used for therapy / exercise as options.

If you plan to replicate this, a few changes would be recommended. The 8 mm rollers could do with larger “drums” over them — about an inch or two in diameter. That helps prevent belt slippage and improves tension adjustment. It ought to be easy to 3D print the add-on drums. The belt might also need support plates between the rollers to prevent sag. The speed display needs to be in linear units — feet per minute or meters per minute, rather than motor rpm. And while the electronics includes a RS-485 interface, it would help to add RS-232, RS-422 and Ethernet in the mix.

While this is a simple build, it can form the basis for a series of add-ons and extensions to help students learn more about automation and control systems. Or maybe you want a conveyor belt in your basement, for some reason.

If you’ve spent any time on a factory or plant floor, it is a good bet you’ve run into PLCs (Programmable Logic Controllers). These are rugged computers that do simple control and monitoring functions, usually using ladder logic to set their programs. [plc4u] wanted to connect a smart card reader to an Allen Bradley PLC, so he turned to an Arduino to act as a go-between.

The Arduino talks to a USB card reader using a USB host shield. Then it communicates with the PLC using an RS232 link and the DF1 protocol that most Allen Bradley PLCs understand. You may not need a smart card, but once you know how to communicate between an Arduino and the PLC, you could do many different projects that leverage other I/O devices and code available on the Arduino and connects to existing PLC installations. Just remember that you’ll probably need to ruggedize the Arduino a bit to survive and be safe to the same level as a PLC (which might include a NEMA enclosure or even an explosion-proof box).

We’ve covered more than one open source PLC project before. If you want to learn more about the ladder logic PLCs use, there’s a good video on the subject. The video below, however, shows the smart card reader in action.

PLC Photo: By Cmarcante (Own work) [CC BY-SA 3.0], via Wikimedia Commons