Teardown: LED Bulb Yields Tiny UPS

April 23, 2018 by Tom Nardi 90 Comments

Occasionally you run across a product that you just know is simply too good to be true. You might not know why, but you’ve got a hunch that what the bombastic phrasing on the package is telling you just doesn’t quite align with reality. That’s the feeling I got recently when I spotted the “LED intellibulb Battery Backup” bulb by Feit Electric. For around $12 USD at Home Depot, the box promises the purchaser will “Never be in the dark again”, and that the bulb will continue to work normally for up to 3.5 hours when the power is out. If I could repurpose that to make a tiny UPS for a microcontroller project of my own, it could be even more useful.

Now an LED light bulb with a battery in the base isn’t exactly rocket science, we can understand the product conceptually at a glance. But as they say, the devil is in the details. The box claims the bulb consumes 8.5 watts, but a battery with enough capacity to run such a load for 3.5 hours would be far too large to fit inside of a light bulb. Obviously there’s more to the story.

On the side of the box, in the smallest font used on the whole package, we get our clue. The bulb drops down to 200 lumens when in battery backup mode, or roughly as bright as a cheap LED flashlight. Now things are starting to come together. Without even opening the device, we can be fairly sure it will contain two separate arrays of LEDs: one low set for battery, and a brighter set to run when the bulb has AC power.

Still, I tend to be of the opinion that anything less than $20 or so is worth cracking open to see what makes it tick. Even if the product itself is underwhelming, there’s a chance the internal components could be useful or interesting. With that in mind, let’s see what’s inside a battery backup light bulb, and what we might be able to do with it.

Continue reading “Teardown: LED Bulb Yields Tiny UPS” →

Two-Cent Temperature Sensors

April 16, 2018 by Elliot Williams 89 Comments

When they need to add temperature control to a project, many hackers reach for a K-type thermocouple for their high-temperature needs, or an integrated temperature-sensing IC when it doesn’t get that hot. The thermocouple relies on very small currents and extremely high gain, and you pretty much need a dedicated IC to read it, which can be expensive. The ICs aren’t as expensive, but they’re basically limited to boiling water. What do you do if you want to control a reflow oven?

There’s a cheaper way that spans a range between Antarctic winter and molten solder, and you’ve probably already got the parts on your shelf. Even if you don’t, it’s only going to run you an extra two cents, assuming that you’ve already got a microcontroller with an ADC in your project. The BOM: a plain-vanilla diode and a resistor.

I’ve been using diodes as temperature sensors in three projects over the last year: one is a coffee roaster that brings the beans up to 220 °C in hot air, another is a reflow hotplate that tops out around 210 °C, and the third is a toner-transfer iron that holds a very stable 130 °C. In all of these cases, I don’t really care about the actual numerical value of the temperature — all that matters is reproducibility — so I never bothered to calibrate anything. I thought I’d do it right for Hackaday, and try to push the humble diode to its limits for science.

What resulted was a PCB fire, test circuits desoldering themselves above 190 °C, temperature probes coming loose, and finally a broken ramekin and 200 °C peanut oil all over my desk. Fun times! On the other hand, I managed to get out enough data to calibrate some diodes, and the results are fantastic. The circuits under test included both best practices and the easiest thing that could possibly work, and the results are pretty close. This is definitely a technique that you want to have under your belt for most temperature ranges. The devil is in the details, of course, so read on!

Continue reading “Two-Cent Temperature Sensors” →

Baremetal Rust On The Horizon

March 12, 2018 by Inderpreet Singh 48 Comments

Rust Programming Langauge has grown by leaps and bounds since it was announced in 2010 by Mozilla. It has since become a very popular language owing to features such as memory safety and its ownership system. And now, news has arrived of an Embedded Devices Working Group for Rust aiming at improving support for microcontrollers.

Rust is quite similar to C++ in terms of syntax, however Rust does not allow for null or dangling pointers which makes for more reliable code in the hands of a newbie. With this new initiative, embedded development across different microcontroller architectures could see a more consistent and standardized experience which will result in code portability out of the box. The proposed improvements include IDE and CLI tools for development and setup code generation. There is also talk of RTOS implementations and protocol stack integration which would take community involvement to a whole new level.

This is something to be really excited about because Rust has the potential to be an alternative to C++ for embedded development as rust code runs with a very minimal runtime. Before Arduino many were afraid of the outcome of a simple piece of code but with rust, it would be possible to write memory-safe code without a significant performance hit. With a little community support, Rust could be a more efficient alternative. We have seen some Rust based efforts on ARM controllers and have covered the basics of Rust programming in the past if you want to get started. Good times ahead for hardware hackers.

Tiny Function Generator On The ATtiny85, Complete With OLED

March 2, 2018 by Donald Papp 4 Comments

It’s easy to have a soft spot for “mini” yet perfectly functional versions of electronic workbench tools, like [David Johnson-Davies]’s Tiny Function Generator which uses an ATtiny85 to generate different waveforms at up to 5 kHz. It’s complete with a small OLED display to show the waveform and frequency selected. One of the reasons projects like this are great is not only because they tend to show off some software, but because they are great examples of the kind of fantastic possibilities that are open to anyone who wants to develop an idea. For example, it wasn’t all that long ago that OLEDs were exotic beasts. Today, they’re available off the shelf with simple interfaces and sample code.

The Tiny Function Generator uses a method called DDS (Direct Digital Synthesis) on an ATtiny85 microcontroller, which [David] wrote up in an earlier post of his about waveform generation on an ATtiny85. With a few extra components like a rotary encoder and OLED display, the Tiny Function Generator fits on a small breadboard. He goes into detail regarding the waveform generation as well as making big text on the small OLED and reading the rotary encoder reliably. His schematic and source code are both available from his site.

Small but functional microcontroller-based electronic equipment are nifty projects, and other examples include the xprotolab and the AVR-based Transistor Tester (which as a project has evolved into a general purpose part identifier.)

Laser Galvo Control Via Microcontroller’s DAC

February 15, 2018 by Donald Papp 33 Comments

Mirror galvanometers (‘galvos’ for short) are the worky bits in a laser projector; they are capable of twisting a mirror extremely quickly and accurately. With two of them, a laser beam may be steered in X and Y to form patterns. [bdring] had purchased some laser galvos and decided to roll his own control system with the goal of driving the galvos with the DAC (digital to analog) output of a microcontroller. After that, all that was needed to make it draw some shapes was a laser and a 3D printed fixture to hold everything in the right alignment.

The galvos came with drivers to take care of the low-level interfacing, and [bdring]’s job was to make an interface to translate the 0 V – 5 V output range of his microcontroller’s DAC into the 10 V differential range the driver expects. He succeeded, and a brief video of some test patterns is embedded below.

Continue reading “Laser Galvo Control Via Microcontroller’s DAC” →

ATtiny Chip Abused In RFID Application

January 5, 2018 by Bryan Cockfield 21 Comments

One of Atmel’s smallest microcontrollers, the ATtiny, is among the most inexpensive and reliable chips around for small applications. It’s also one of the most popular. If you don’t need more than a few inputs or outputs, there’s nothing better. As a show of its ability to thrive under adverse conditions, [Trammell Hudson] was able to shoehorn an ATtiny into an RFID circuit in a way that tests the limits of the chip design.

The RFID circuit only uses two of the ATtiny’s pins and neither of which is the ground or power pin. The ATtiny is equipped with protective diodes on its input pins, and if you apply an AC waveform to the input pins, the chip is able to use the leakage current to power itself. Once that little hurdle is crossed, the ATtiny can do the rest of its job handling the RFID circuitry.

This project takes a deep dive into the internals of the ATtiny. If you’ve ever wondered what was going on inside of everyone’s favorite tiny microcontroller, or if you’re looking for an RFID circuit that keeps parts counts to an absolute minimum, this is the project for you. The ATtiny is more than just a rugged, well-designed chip, though. It’s capable of a lot more than such a small chip should be able to.

Thanks to [adnidor] for the tip!

Balance Like A Mountain Goat On This Simple Stewart Platform

December 27, 2017 by Dan Maloney 4 Comments

No goats were harmed in the making of this 3-DOF Stewart platform for [Bruce Land]’s microcontrollers course at Cornell.

If the name “Stewart platform” doesn’t ring a bell, the video below will help you out. [Team Microgoats] built a small version of the mechanical system commonly seen in flight simulators, opting for 3 DOF to simplify the design. Their PIC32-controlled steppers can wobble and weave the table in response to inputs from an MPU-6050 six-axis accelerometer embedded in the base of a 3D-printed goat. Said goat appears to serve no other role in the build, but goats are cool, so why not? And if you’ve ever seen a mountain goat frolicking across a sheer vertical rock face like it was walking across a parking lot, you’ll understand the connection to the balance and control offered by a Stewart platform.

[Bruce Land]’s course is always a bonanza of neat projects that pop up in our tipline this time of year, like a POV box fan, a coin cell Rickrolling throwie, and a dynamometer for small electric motors.

Continue reading “Balance Like A Mountain Goat On This Simple Stewart Platform” →