Author: Bryan Cockfield

1760 Articles

Adding Human Detection To Home Automation

August 29, 2024 by 39 Comments

Radar made a huge impact when it was first invented, allowing objects to be detected using radio waves which would normally be difficult or impossible to observe through other means. Radio waves of all frequencies can be used for radar as well, whether that’s detecting ships beyond the horizon, tracking aircraft near an airport, penetrating the ground, or imaging objects with a high resolution. At the millimeter wavelength it’s fairly easy to detect humans with the right hardware, and using some inexpensive radar modules [Tech Dregs] shows us how to add this capability a home automation system.

Since these modules aren’t trying to image humans with fine detail or detect them at long range, the hardware can be fairly inexpensive. [Tech Dregs] is using the LD2410B modules which have not only an on-board microcontroller but also have the radio antennas used for radar built right onto the PCB. They have a simple binary output which can communicate whether or not a human is detected, but there’s also UART for communicating more details about what the module senses in the room. [Tech Dregs] is using this mode to connect the modules to Home Assistant, where they will be used to help automate his home’s lighting.

The only significant problem he had setting these modules up was getting them built into an enclosure. The short wavelengths used in this type of radar module don’t penetrate solid objects very well at all, so after trying to hide one behind an e-ink screen he eventually settled on hollowing out a space in a bezel with very thin plastic between the module and the room. If you need more out of your radar modules than object detection, though, you can always try building a pulse compression radar which can provide much more accurate ranging of objects.

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A Non-Musical Use Case For 8-Track

August 28, 2024 by 23 Comments

There was a time in the not-too-distant past when magnetic tape was the primary way of listening to and recording audio. Most of us are familiar with the cassette tape, a four-track system that plays first one side of the tape, then the other. There was the eight-track tape as well which did not have quite as much popularity or longevity but did have a few interesting features that [Serial Hobbyism] took advantage of to make an interactive game.

The defining feature of the eight-track system, beyond the obvious eight tracks on the tape, is that the tape runs in a continuous loop, never needing to be stopped or flipped over. Instead, four buttons select pairs of the eight tracks, moving a head immediately to make the switch on-the-fly. [Serial Hobbyism]’s game plays a trivia-style audio recording and asks the player to answer questions by pushing one of the four “program” buttons to switch tracks. If the correct track is selected, the recorded audio congratulates the player and then continues on with the game. Likewise, if an incorrect track is selected, the recording notes that and the game continues.

Another interesting feature of this game is that it can be played without modifying an eight-track player, as the selectable tracks are a core function of this technology. They can be used in a similar way as cassette tapes to store computer data and a data recorder similar to the eight-track system was used on the Voyager space probes, although these only bear a passing resemblance.

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Hidden Gutter Antenna Keeps HOA Happy

August 27, 2024 by 142 Comments

The United States and a few other countries have an astounding array of homeowners’ associations (HOAs), local organizations that exert an inordinate influence on what homeowners can and can’t do with their properties, with enforcement mechanisms up to foreclosure. In the worst cases they can get fussy about things like the shade of brown a homeowner can paint their mailbox post, so you can imagine the problems they’d have with things like ham radio antennas. [Bob] aka [KD4BMG] has been working on tuning up his rain gutters to use as “stealth” antennas to avoid any conflicts with his HOA.

With the right antenna tuner, essentially any piece of metal can be connected to a radio and used as an antenna. There are a few things that improve that antenna’s performance, though. [Bob] already has an inconspicuous coax connector mounted on the outside of his house with an antenna tuner that normally runs his end-fed sloper antenna, which also looks like it includes a fairly robust ground wire running around his home. All of this is coincidentally located right beside a metal downspout, so all this took to start making contacts was to run a short wire from the tuner to the gutter system.

With the tuner doing a bit of work, [Bob] was able to make plenty of contacts from 10 to 80 meters, with most of the contacts in the 20 – 30 meter bands. Although the FCC in the US technically forbids HOAs from restricting reasonable antennas, if you’d rather not get on the bad side of your least favorite neighbors there are a few other projects from [Bob] to hide your gear.

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Creating Customized Diffraction Lenses For Lasers

August 23, 2024 by 3 Comments

[The Thought Emporium] has been fascinated by holograms for a long time, and in all sorts of different ways. His ultimate goal right now is to work up to creating holograms using chocolate, but along the way he’s found another interesting way to manipulate light. Using specialized diffraction gratings, a laser, and a few lines of code, he explores a unique way of projecting hologram-like images on his path to the chocolate hologram.

There’s a lot of background that [The Thought Emporium] has to go through before explaining how this project actually works. Briefly, this is a type of “transmission hologram” that doesn’t use a physical object as a model. Instead, it uses diffraction gratings, which are materials which are shaped to light apart in specific ways. After some discussion he demonstrates creating diffraction gratings using film. Certain diffraction patterns, including blocking all of the light source, can actually be used as a lens as the light bends around the blockage into the center of the shadow where there can be focal points. From there, a special diffraction lens can be built.

The diffraction lens can be shaped into any pattern with a small amount of computer code to compute the diffraction pattern for a given image. Then it’s transferred to film and when a laser is pointed at it, the image appears on the projected surface. Diffraction gratings like these have a number of other uses as well; the video also shows a specific pattern being used to focus a telescope for astrophotography, and a few others in the past have used them to create the illusive holographic chocolate that [The Thought Emporium] is working towards.

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Get More Freedom With This Guitar Pedal

August 19, 2024 by 13 Comments

When the electric guitar was first produced in the 1930s, there was some skepticism among musicians as to whether or not this instrument would have lasting impact or be a flash-in-the-pan novelty. Since this was more than a decade before the invention of the transistor, it would have been hard then to imagine the possibilities that a musician nowadays would have with modern technology to shape the sound of an instrument like this. People are still innovating in this space as well as new technology appears, like [Gary Rigg] who has added a few extra degrees of freedom to a guitar effects pedal.

A traditional expression pedal, like a wah-wah pedal, uses a single motion to change an aspect of the sound of the guitar, and is generally controlled with the musician’s foot. [Gary]’s pedal, on the other hand, can be manipulated in three different ways to control separate elements of the instrument’s sound. It can be pitched forward and back like a normal effects pedal, but also rolled side-to-side and twisted around its yaw axis. The pedal has a built-in IMU to measure the various position changes of the pedal, which is then translated by an RP2040 microcontroller to a MIDI signal which controls the three different aspects of the sound digitally.

While the yaw motion might be difficult for a guitarist to create with their foot while playing, the idea for this pedal is still excellent. Adding in a few more degrees of freedom gives the musician more immediate control over the sound of their instrument and opens up ways of playing that might not be possible or easy with multiple pedals, with the MIDI allowing for versatility that might not be available in many analog effects pedals. Not every pedal needs MIDI though; with the help of a Teensy this digital guitar pedal has all its effects built into a self-contained package.

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Rebuilding The First Digital Personal Computer

August 16, 2024 by 15 Comments

When thinking of the first PCs, most of us might imagine something like the Apple I or the TRS-80. But even before that, there were a set of computers that often had no keyboard, or recognizable display beyond a few blinking lights. [Artem Kalinchuk] is attempting to recreate one of these very early digital computers, the Kenbak-1, using as many period-correct parts as possible.

Considered by many to be the world’s first personal computer, the Kenbak-1 was an 8-bit machine with 256 bytes of memory, using TTL integrated circuits for the logic as there was no commercially available microprocessor available at the time it was designed. For [Artem]’s build, most of these parts can still be sourced including the 7400-series chips and carbon resistors although the shift registers were a bit of a challenge to find. A custom PCB was built to replicate the original, and with all the parts in order it’s ready to be assembled and put into a case which was built using the drawings for the original unit.

Although [Artem] plans to build a period-correct linear power supply for this computer, right now he’s using a modern switching power supply for testing. The only other major components that are different are the status lamps, in this case switched to LEDs because he wasn’t able to source incandescent bulbs that drew low enough current, and the switches which he’s replaced with MX-style keys. We’ll stay tuned as he builds and tests this over the course of several videos, but in the meantime if you’re curious how this early computer actually worked we featured an emulator for it a while back.

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The Sunchronizer Keeps Your Solar Panel Aligned

August 15, 2024 by 35 Comments

In the past few years, the price-per-watt for solar panels has dropped dramatically. This has led to a number of downstream effects beyond simple cost savings. For example, many commercial solar farms have found that it’s now cheaper to install a larger number of panels in fixed positions, rather than accepting the extra cost, maintenance, and complexity of a smaller number panels that use solar tracking to make up the difference. But although this practice is fading for large-scale power production, there are still some niche uses for solar tracking. Like [Fabian], if you need to maximize power production with a certain area or a small number of panels you’ll wan to to build a solar tracker.

[Fabian]’s system is based on a linear actuator which can tilt one to four panels (depending on size) in one axis only. This system is an elevation tracker, which is the orientation generally with respect to latitude, with a larger elevation angle needed in the winter and a lower angle in the summer. [Fabian] also designs these to be used in places like balconies where this axis can be more easily adjusted. The actuator is controlled with an ESP32 which, when paired with a GPS receiver, can automatically determine the sun’s position for a given time of day and adjust the orientation of the panel to provide an ideal elevation angle on a second-by-second basis. The ESP32 also allows seamless integration with home automation systems like SmartHome as well.

Although this system only tracks the sun in one axis right now, [Fabian] is working on support for a second axis which mounts the entire array on a rotating table similar to an automatic Lazy Susan. This version also includes a solar tracking sensor which measures solar irradiance in the direction the panel faces to verify that the orientation of the panel is maximizing power output for a given amount of sunlight. Tracking the sun in two axes can be a complicated problem to solve, but some solutions we’ve seen don’t involve any GPS, programming, or even control electronics at all.

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