# How The Power Gets To The Outlet

[Practical Engineering] is ready to explain how power substations get electricity to you in his latest video, which you can see below.  One of the things we always notice when talking to people either in our community or outside it is that most people have no idea how most of the modern world works.

Ask your non-technical friend to explain how a cell phone works or how a hard drive stores data and you aren’t likely to get a very good answer. However, even most of us are only focused on some particular aspect of electronics. There are a lot of people who hack on robots or radios. The AC power grid,though isn’t something a lot of people work with as a hobby. Do you know exactly what goes on in that substation you pass every day on your commute? If you don’t, you’ll learn something in the video.

# FM Signal Detection The Pulse-Counting Way

Compared to the simple diode needed to demodulate AM radio signals, the detector circuits used for FM are slightly more complicated. Wrapping your head around phase detectors, ratio detectors, discriminators, and quadrature detectors can be quite an exercise. There’s another demodulation method that’s not so common, but thankfully it’s also pretty easy to understand: the pulse counting detector.

As [Allan (W2AEW)] notes in the video below, pulse counting is a bit of a misnomer. Pulse counting works by generating a narrow, fixed-width square wave pulse at a set point in the received FM signal’s waveform, usually at the zero-crossing point. Since the frequency of the modulated carrier changes, the duty cycle of the resulting pulse train varies. That means there will be a fixed number of pulses, but by taking the average voltage of the pulse train, we can tease out the original audio frequency signal.

Simple in theory is often more complicated in practice, and [W2AEW] goes into some detail about those complications, such as needing to use a down-converter to make the peak-to-peak frequency deviation in the pulse train more easily detectable. As is his style, he walks us through a test circuit to prove that the theory works in practice. A simple two-transistor circuit generates the pulses at the zero-crossing point, a low-pass filter cleans up the signal, and a cheap audio amplifier reproduces the original audio. It’s a crude circuit to be sure, relying on the stray capacitance of the breadboard to work, but it proves the point and serves as a jumping-off point for further experiments – perhaps using an Arduino to count the pulses?

We always enjoy [W2AEW]’s videos and learn a lot from them. Not long ago we featured another of his videos talking about the mysteries of RF modulation; SSB, anyone?

# Monitoring An Electric Fence With LoRaWAN

Making sure that an electric fence which is keeping one’s cattle and sheep from wandering off is still working properly seems like a fairly daunting task, especially when this fence is quite a distance from one’s home so checking up on it is time-consuming. After a friend of [kiu] got called a few times by the police because some of the sheep had pulled a prison break, the obvious technological solution was to IoT-enable the fence with LoFence.

This solution is nothing if not elegant in its simplicity. For phoning home with status data, the system uses the Microchip RN2483 IC, which handles pretty much all aspects of LoRaWAN, so that one merely has to send data to its serial interface to transmit. Because this system uses The Things Network (TTN) there are no service costs due to the low data rates. This was the easy part, aside from having to add a LoRaWAN gateway to boost the signal in the area with the electric fence.

With that side covered, the rest of the build features an AVR ATmega328p MCU, a resistor divider and op-amp (TLV9062) along with some passives. The resulting circuit measures voltage, essentially to detect whether the fence is still forming a full circuit. Hacking into the little box that energizes the fence might be a possible upgrade there, but at least it is a fairly uncomplicated way to measuring things. Electric fences do work best with a voltage on them, after all.

At the other end of the LoRaWAN network, the data is parsed and analyzed by a service so that it can be displayed on a Grafana dashboard, ensuring that a single glance suffices to see the current state of the fence and whether one has to dash out in the rain at 1 AM to fix it or not.

# Skid Steer Mows Airport Grass Autonomously

Sure, mowing the lawn is a hassle. No one really wants to spend their time and money growing a crop that doesn’t produce food, but we do it anyway. If you’re taking care of a quarter acre in the suburbs it’s not that much of a time sink, but if you’re taking care of as much grass as [Roby], you’d probably build something similar to his autonomous skid-steer mower, too.

This thing isn’t a normal push mower outfitted with some random electronics, either. This is a serious mower that is essentially a tractor with blades attached to it. Since it’s a skid steer, it turns by means of two handles that control the speed of the left or right drive wheels. Fabricating up some servo linkages to attach them to specialized servos takes care of the steering portion, and the brain is ArduPilot hooked up to a host of radios, GPS, and a compass to allow it to drive all around the runways at the airport without interfering with any aircraft.

This is a serious build and goes into a lot of detail about how servos and linkages should behave, how all the software works, and the issues of actually mounting everything to the mower. The entire project is open source too, so even if you don’t have a whole airport runway to mow you might be able to find something in there to help with your little patch of grass.

Thanks to [Vincent] for the tip!

# Cat Litter Tray Joins The Internet Of Things

Keeping a cat as a pet can be rewarding, but it’s always important to consider how to handle the mess – and we’re not just talking about the tea cups pushed off tables here. To handle just this task, [Igor] decided to hook his cat litter box up to the internet of things.

Monitoring the litter box brings several useful advantages. Load cells enable the weight of the litter tray to be monitored, allowing sand levels and the weight of the cats to be checked at regular intervals. Additionally, a door sensor keeps a record of comings and goings, giving an idea of how frequently the box has been used, and whether or not it may be time for cleaning. It’s all powered by an ESP32, hooked up to the Thingspeak platform. This allows for easy graphing and analysis of the data collected from the system. The electronics is then neatly installed in an attractive two-tone 3D printed enclosure with a pleasing cat motif.

It’s a great example of using some cheap off-the-shelf parts to ease the regular tasks of daily life. Building your own gear can be beneficial too, especially when Big Litter implements DRM on their hardware.

# Global Radiation Montoring And Tracking Nuclear Disasters At Home

Many of us don’t think too much about radiation levels in our area, until a nuclear disaster hits and questions are raised. Radiation monitoring is an important undertaking, both from a public health perspective and as a way to monitor things like weapon development. So why is it done, how is it done, and what role can concerned citizens play in keeping an eye on things?

# Everything You Want To Know About The Cheapest Processors Available

Those of us who use microprocessors in our work will be familiar with their cost, whether we are buying one or two for a project or ten million on reels for a production run. We’re used to paying tens of cents or maybe even a dollar for a little microcontroller in single quantities, and these are probably the cheapest that we might expect to find.

There is a stratum of cheaper devices though, usually from Chinese manufacturers with scant data in English and difficult to source in Europe or the Americas. These chips cost under ten cents each, a figure which seems barely credible. To shed some light upon this world, [cpldcpu] has produced a run-down of some of the available families that even if you will never work with such an inexpensive option still makes for a fascinating read.

These processors are not the type of component you would use for high intensity tasks so it’s probable that you will not be mining cryptocurrency on a brace of them. Thus their architecture is hardly cutting-edge, with the venerable PIC12 being their inspiration and in some cases their direct copy. These are all write-once devices and some of their toolchains are variable in accessibility, but perhaps they aren’t as terrible as some would have you believe. If you are looking for inspiration, we’ve featured one of them before.

TL;DR: the Padauk PFS173, at just under \$0.09, has an open-source toolchain and a decent set of peripherals.

Thanks [WilkoL] for the tip.

Image: A real PIC12 die shot. ZeptoBars [CC BY 3.0]