The Right Tools For The Job

February 6, 2021 by Elliot Williams 16 Comments

We’re knee-deep in new microcontrollers over here, from the new Raspberry Pi Pico to an engineering sample from Espressif that’s right now on our desk. (Spoiler alert, review coming out Monday.) And microcontroller peripherals are a little bit like Pokemon — you’ve just got to catch them all. If a microcontroller doesn’t have 23 UARTS, WiFi, Bluetooth, IR/DA, and a 16-channel 48 MHz ADC, it’s hardly worth considering. More is always better, right?

No, it’s not. Chip design is always a compromise, and who says you’re limited to one microcontroller per project anyway? [Francesco] built a gas-meter reader that reminded to think outside of the single-microcontroller design paradigm. It uses an ATtiny13 for its low power sleep mode, ease of wakeup, and decent ADCs. Pairing this with an ESP8266 that’s turned off except when the ATtiny wants to send data to the network results in a lower power budget than would be achievable with the ESP alone, but still gets his data up into his home-grown cloud.

Of course, there’s more complexity here than a single-micro solution, but the I2C lines between the two chips actually form a natural division of work — each unit can be tested separately. And it’s using each chip for what it’s best at: simple, low-power tasks for the Tiny and wrangling WiFi on the ESP.

Once you’ve moved past the “more is better” mindset, you’ll start to make a mental map of which chips are best for what. The obvious next step is combination designs like this one.

Proto-TV Tech Lies Behind This POV Clock

February 6, 2021 by Dan Maloney 11 Comments

If it weren’t for persistence of vision, that quirk of biochemically mediated vision, life would be pretty boring. No movies, no TV — nothing but reality, the beauty of nature, and live performances to keep us entertained. Sounds dreadful.

We jest, of course, but POV is behind many cool hacks, one of which is [Joe]’s neat Nipkow disk clock. If you think you’ve never heard of such a thing, you’re probably wrong; Nipkow disks, named after their 19th-century inventor Paul Gottlieb Nipkow, were the central idea behind the earliest attempts at mechanically scanned television. Nipkow disks have a series of evenly spaced, spirally arranged holes that appear to scan across a fixed area when rotated. When placed between a lens and a photosensor, a rudimentary TV camera can be made.

For his Nipkow clock, though, [Joe] turned the idea around and placed a light source behind the rotating disk. Controlling when and what color the LEDs in the array are illuminated relative to the position of the disk determines which pixels are illuminated. [Joe]’s clock uses two LED arrays to double the size of the display area, and a disk with rectangular apertures. The resulting pixels are somewhat keystone-shaped, but it doesn’t really distract from the look of the display. The video below shows the build process and the finished clock in action.

The key to getting the look right in a display like this is the code, and [Joe] put in a considerable effort for his software. If only the early mechanical TV tinkerers had had such help. [Jenny List] did a nice write-up on the early TV pioneers and their Nipkow disk cameras; we’ve also seen other Nipkow displays before, but [Joe]’s clock takes the concept to another level.

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Open-Source Thermostat Won’t Anger Your Landlord

February 6, 2021 by Anool Mahidharia 51 Comments

[Nathan Petersen] built a Hackable Open-Source Thermostat to smooth out temperature fluctuations caused by the large hysteresis of the bimetallic strip thermostat in his apartment. While it may be tempting to adjust the “anticipator” to take care of the problem or even replace the bimetallic thermostat with an electronic version, building your own thermostat from scratch is a good way to add to your project portfolio while making your way through college. Plus, he got to hone his hardware and software design chops.

The hardware is designed around the STM32, using a cheap, minimal variant since the device just needs to sense temperature and control the furnace in on-off mode. The TMP117 high-accuracy, low-power, temperature sensor was selected for temperature measurement since accuracy was an essential feature of the project. Dry-contact output for the furnace is via a normally-open solid state relay (opto-isolator). For the user interface, instead of going the easy-route and using an I²C/SPI OLED or LCD display, [Nathan] used three 7-segment LED displays, each driven by an 8-channel constant current driver. The advantage is that the display can be viewed from across the room, and it’s brightness adjusted via PWM. Temperature set-point adjustment is via a simple slide potentiometer, whose analog voltage is read by the micro-controller ADC. To remind about battery replacement, a second ADC channel on the micro-controller monitors the battery voltage via a voltage divider. The PCB components are mostly surface mount, but the packages selected are easy enough to hand solder.

[Nathan]’s Github repo provides the hardware and firmware source files. The board is designed in Altium, but folks using KiCad can use either the awesome Altium2KiCad converter or the online service for conversion. (The results, with some minor errors that can be easily fixed, are quite usable.) Serendipitously, his PCB layout worked like a charm the first time around, without requiring any rework or bodge wires.

The firmware is a few hundred lines of custom bare-metal C code, consisting of drivers to interface with the hardware peripherals, a UI section to handle the user interface, and the control section with the algorithm for running the furnace. [Nathan] walks us through his code, digging into some control theory and filtering basics. After making a few code tweaks and running the thermostat for some time, [Nathan] concludes that it is able to achieve +0.1°F / -0.5°F temperature regulation with furnace cycles lasting about 10-15 minutes (i.e. 4-6 cycles per hour). Obviously, his well insulated apartment and a decent furnace are also major contributing factors. Moving on, for the next version, [Nathan] wants to add data collection capabilities by adding some memory and SD card storage, and use an RTC to allow seasonal adjustments or time-based set-points.

This is his first attempt at a “functional’ useful project, but he does love to build the occasional toy, such as this POV Top.

Building A Continuously Variable Transmission With Lego

February 5, 2021 by Lewin Day 13 Comments

The first continuously variable transmission fitted to an automobile actually has its roots in the late 19th century, though the technology has only become popular in the last two decades or so. While a relatively complex technology in its modern automotive form, it’s still possible to illustrate the basic principles with everyone’s favourite mechanical learning toy – Lego.

The transmission as built isn’t great at high torque delivery, as the belt tends to slip on the smooth plastic of the cones. Increasing friction would help.

The build consists of a Lego motor driving the transmission’s input shaft, upon which a cone is mounted. A similar cone is mounted on the output shaft, and a rubber belt stretched between the two. With the cones mounted in opposing directions, the gear ratio can be continually varied by changing where upon the cones the belt rides. By riding on the small diameter section of the input cone, the belt correspondingly rides on the large diameter section of the output cone, leading to a slower, high torque output. By sliding the belt to the other end of the cone, the ratios are reversed, leading to high output speed with less torque.

The demonstration works somewhat differently than modern automotive models, but the basic concept is the same. It’s also limited in its torque transfer ability by the coefficient of friction of the plastic Lego parts. Despite this, it’s a quick way to illustrate the mechanisms at play, and where some of the common losses are in such a system. If you prefer your gearboxes of a more classic sequential design, we’ve seen those too, of course. Video after the break.

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Sequencing DNA For Metagenomics

February 5, 2021 by Al Williams 15 Comments

If someone brought you an odd piece of electronic hardware and you wanted to identify it, you’d probably look for markings on the outside first. If that didn’t work out, you might look under the cover and read some markings on the board or key components. However, in a tough case, you might dump the firmware and try to guess what the device is or what it does by examining the code that makes it run. That’s kind of what [Ciro] did. Wanting to determine the bacteria in a water sample led to using relatively inexpensive DNA sequencing hardware to look at the DNA present in the samples. This would have been a huge undertaking for a well-funded lab just a few short years ago. Now it just takes a USB device and some software.

Of course, inexpensive is in the eye of the beholder. The micropore sequencer costs about $500 and has a one-time use consumable cost of about $500, although that’s enough to process about 10 human genomes. The technology depends on using a small pore only large enough to pass one strand of DNA at a time. Blocks of nucelotides cause different amounts of electrical current to flow through the pore.

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Custom Ignition For A Citroën Mehari

February 5, 2021 by Lewin Day 42 Comments

The 20th century saw a great many cheap, utilitarian vehicles enter the marketplace. Cars like the Mini and the original Jeep offered low-cost, no-frills motoring. However, they were also decidedly low-tech, and not as reliable as modern cars by a long shot. The Citroën Mehari fits into this category neatly, and when [FVFILIPPETTI] grew tired of the unreliable points ignition system, he decided to build a more modern replacement.

The system is based around at ATmega328, the venerable chip many are familiar with from its starring role in the Arduino Uno. The chip tracks engine position with a magnet mounted on the flywheel combined with a hall-effect sensor, passed through an optocoupler to avoid nasty high-voltage spikes from the spark system interfering with the microcontroller. The chip then charges the ignition coil and fires it at the necessary time to ignite the air fuel mixture.

Old-school mechanical ignition systems were, if we’re honest, terrible compared to more modern solutions. This build has rewarded [FVFILIPPETTI] with a far more reliable ride, which we’re sure is very satisfying. If all this hacking has you thirsty for an automotive project of your own, dive into our primer on how to get into cars!

LoRa Messenger Does Its Best BlackBerry Impression

February 5, 2021 by Tom Nardi 23 Comments

While the de facto smartphone design ultimately went in a different direction, there’s no denying the classic BlackBerry layout offered some compelling advantages. It was a gadget primarily designed to send and receive emails and text messages, and it showed. So is it really any wonder [MSG] would build his pocket-sized LoRa messengers in its image?

Of course, he did have some help. The communicators use the Keyboard FeatherWing by [arturo182], which puts a surplus BlackBerry Q10 keyboard on a custom PCB designed to accept a board from Adafruit’s Feather collection. [MSG] ended up pairing his with a Feather M4 because he wanted to work with CircuitPython, with a 900 MHz LoRa FeatherWing along for the ride. He notes that switching his code over to Arduino-flavored C would allow him to use the Feather M0 that features integrated LoRa; a change that would allow him to make the gadget a bit thinner.

Inside the 3D printed enclosure, He’s made room for a 3.7 V 1800 mAh pouch battery that should provide plenty of runtime. There’s also an external antenna with a uFL pigtail for connecting to the radio. The case is held together with heat-set inserts, which should make it more than robust enough to handle a few adventures.

[MSG] says slight variations in hardware versions means his STLs might need a little tweaking to fit your components, and warns that his code is basically just a mashup of examples he found online, but he’s still sharing the goods for anyone who wants to reach out and touch someone without all that pesky infrastructure in the way.

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