The measurement results of: (a) RSSI in dBm collected from gateway 2 and (b) soil moisture during the winter period. (Credit: Maja Škiljo et al., 2022)

Using LoRa Nodes As Soil Moisture Sensing Antennas

October 2, 2023 by Maya Posch 9 Comments

Implementation of LoRaWAN-based soil moisture sensing device. (Credit: Maja Škiljo et al., 2022)

Although we generally think of Internet of Things (IoT) and similar devices as things that are scattered around above ground, there are plenty of reasons to also have such devices underground. These so-called IoUT devices are extremely useful when it comes to monitoring underground structures, but communication via radiowaves is obviously impacted when soil is in the way. Although there are ways to get around this, a 2022 paper by Maja Škiljo and colleagues in Sensors covers an interesting way to make use of this signal attenuation property of changing moisture levels in soil.

By quantifying the exact attenuation of the signal received at the gateways, they were able to determine the soil moisture levels around the LoRa node which had been buried at a depth of approximately 14 centimeters. This LoRa node used off-the-shelf components consisting of an ATmega328P-based Arduino Pro Mini and SX1276-based RFM95W LoRa module with a spring antenna.

During experimentation in- and outdoors it was determined that a narrowband, printed (PCB) antenna was optimal for soil moisture sensing purposes. Other than the interesting question of how to keep soil moisture sensing nodes like this powered up over long periods of time (perhaps periodic retrieval to replenish the battery), this would seem to be a very interesting way to monitor the soil moisture levels in something like a field, where each node can provide its own ID and the received signal providing the relevant data in the form of the SNR and other parameters recorded by the gateway.

(Heading image: The measurement results of: (a) RSSI in dBm collected from gateway 2 and (b) soil moisture during the winter period. (Credit: Maja Škiljo et al., 2022) )

Why Walking Tanks Never Became A Thing

October 2, 2023 by Lewin Day 66 Comments

The walking tank concept has always captured imaginations. Whether you’re talking about the AT-AT walkers of Star Wars, or the Dreadnoughts from Warhammer 40,000, they are often portrayed in fiction as mighty and capable foes on the battlefield. These legged behemoths ideally combine the firepower and defense of traditional tanks with the versatility of a legged walking frame.

Despite their futuristic allure, walking tanks never found a practical military application. Let’s take a look at why tracks still rule, and why walking combat machines are going to remain firmly in the realm of fiction for the foreseeable future.

Continue reading “Why Walking Tanks Never Became A Thing” →

How Warehouse Robots Actually Work, As Explained By Amazon

October 2, 2023 by Donald Papp 7 Comments

Amazon has been using robots to manage and automate their warehouses for years. Here’s a short feature on their current robot, Hercules. This is absolutely Amazon tooting their own horn, but if you have been curious about what exactly such robots do, and how exactly they help a busy warehouse work better, it’s a good summary with some technical details.

Amazon claims to have over 750,000 robots across their network.

The main idea is that goods are stored on four-sided shelves called pods. Hercules can scoot underneath to lift and move these pods a little like a robotic forklift, except much smaller and more nimble. Interestingly, the robots avoid rotating shelves as much as possible and are designed to facilitate this. To change direction, Hercules sets the pod down, turns, then picks the pod back up.

The overall system is centralized, but Hercules itself navigates autonomously thanks to a depth-sensing camera and a grid of navigation markers present on the floor throughout the facility. Hercules also can wirelessly sense and communicate with nearby human-worn vests and other robots outside its line of sight.

Essentially, instead of human workers walking up and down aisles of shelves to pick products, the product shelves come to the humans. This means the organization and layout of the shelves themselves can be dynamic, higher density, and optimized for efficient robotic access. Shelves do not need to be in fixed rows or aisles, conform to a human-readable categorical layout, nor do they necessarily need walking space between them.

Sometimes robots really are the right tool for the job, and our favorite product-retrieval robot remains [Cliff Stoll]’s crawlspace warehouse bot, a diminutive device made to access boxes of product — in [Cliff]’s case, Klein bottles — stored in an otherwise quite claustrophobic crawlspace.

Passive Desalination Discovers How To Avoid Salt-Clogging

October 2, 2023 by Donald Papp 15 Comments

Saltwater is plentiful, but no good for drinking. Desalinization is the obvious solution, but a big problem isn’t taking the salt out, it’s where all that leftover salt goes. Excess salt accumulates, crystallizes, collects, and clogs a system. Dealing with this means maintenance, which means higher costs, which ultimately limits scalability.

The good news is that engineers at MIT and in China have succeeded in creating a desalination system that avoids this problem by intrinsically flushing accumulated salt as it is created, keeping the system clean. And what’s more, the whole thing is both scalable and entirely passive. The required energy all comes from gravity and the sun’s heat.

To do this, the device is constructed in such a way that it mimics the thermohaline circulation of the ocean on a small scale. This is a process in which temperature and density differentials drive a constant circulation and exchange. In the team’s system, this ultimately flushes concentrations of salt out of the system before it has a chance to collect.

The entirely passive nature of the device, its scalability, and the fact that it could desalinate water without accumulating salt for years means an extremely low cost to operate. The operating principle makes sense, but of course, it is careful engineering that shows it is actually possible. We have seen projects leveraging the passive heating and circulation of water before, but this is a whole new angle on letting the sun do the work.