2025 Component Abuse Challenge: Heat Activated LED Candles
[Miroslav Hancar] wasn’t satisfied with abusing just a single component for our Component Abuse Challenge. He decided to abuse a whole assembly, in particular, some LED candles.
In this project, LEDs are abused as temperature sensors. When the temperature gets hot enough for long enough, the microcontroller will turn on its LEDs. How? A diode’s forward voltage is temperature-related. By monitoring the forward voltage, the microcontroller can infer the temperature and respond appropriately.
This particular project is really two projects in one, centered around a common theme, heat activation. The first version has four LEDs and, in response to heat, four LEDs flicker to simulate a real candle. The second version is also heat-activated, but it has only one LED. You can snuff out this LED by pinching the top of it with your fingers. You can see a demo of each version in the videos below.
You will find the schematics, Gerber files, and software in the project’s downloadable files. The candles use some of the features of the PIC12F1501 microcontroller, particularly the onboard ADC.
If you’re interested in the PIC12F1501 and LED light displays, be sure to check out SIM Card Connectors and White PCBs Make Huge LED Snowflakes Happen. We wish [Miroslav] every success in the Component Abuse Challenge. The deadline is November 11, so you still have a few days to get your submissions in!
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Teardown of HP Optical Link and Signal Investigations Using Siglent Technology
Anything with a laser has undeniable hacker appeal, even if the laser’s task is as pedestrian as sending data over a fiber optic cable. [Shahriar] from [The Signal Path] must agree, and you can watch as he tears down and investigates a fiber optic link made from old HP equipment in the video below.
He starts with an investigation of the block diagram of the transmitter. In the transmitter, the indium gallium arsenide phosphide laser diode emits light with a 1310-nanometer wavelength. Thermal characteristics in the transmitter are important, so there is thermal control circuitry. He notes that this system only works using amplitude modulation; phase modulation would require more expensive parts. Then it’s time to look at the receiver’s block diagram. Some optics direct the light signal to a PIN diode, which receives the signal and interfaces with biasing and amplifying circuitry.
Having explained the operation of the transmitter and receiver, he takes both units apart and has a close look at the internals, with particular attention to the business ends of the transmitter and receiver, which have been carefully mechanically calibrated. He uses an optical spectrum analyzer to verify the laser wavelength and power, then runs the signal through a vector network analyzer. He also uses an arbitrary waveform generator and a vector signal generator to show that radio over fiber would also be feasible. Finally, he captures an eye diagram on an oscilloscope and measures voltage with a digital multimeter.
If you’re interested in fiber optics, you might enjoy A Brief History of Optical Communication.
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Autopsy of a First-Generation RX7 Mazda Rotary Car Engine
In theory, Wankel-style rotary internal combustion engines have many advantages: they ditch the cumbersome crankcase and piston design, replacing it with a simple, single-chamber design and a thick, plectrum-shaped chunk of metal that spins around inside that chamber to create virtual combustion chambers. This saves weight and maximizes performance-to-weight. Unfortunately, these types of engines are also known for burning a lot of oil and endless seal troubles, especially with early rotary Mazda engines that easily died.
Yet even 1980 versions were not without issues, a case in point is the Mazda 1st gen RX7 with a 12A rotary engine that the [Baked Beans Garage] over at YouTube got their paws on. Starting with unsuccessful attempts to make the car start, the next step was to roll the car into the morgue garage for a full teardown of the clearly deceased engine.
About 35 minutes into the video, we get to the teardown of the engine, with its parts contrasted with those of a newer revision rotary engines alongside illustrations of their functioning, making it as much an autopsy as a detailed introduction to these rotary engines. Technically, they also aren’t the original DKM-style Wankel engines, but a KKM-style engine, as designed by [Hanns-Dieter Paschke]. [Wankel] didn’t like the eccentric KKM design, as he thought it’d put too much stress on the apex seals, but ultimately the more economical KKM design was further developed.
During the autopsy of the 12A revision Mazda engine, it becomes clear that it was likely overheating that killed the engine over the course of years of abuse, along with ‘chatter’ marks of the apex seals destroying the inner chrome coating. This would have compromised compression and with it any chance of the engine running, not unlike a piston engine with badly scored cylinder walls after ingesting some metal chunks.
While the Mazda 12B and subsequent designs addressed many of the issues with the early rotary engines, its use was limited to some sports models, ending in 2012 with the RX-8. The currently produced Mazda MX-30 does use a rotary engine again in its plug-in hybrid version, but it’s only as a range extender engine that drives a generator. Looking at the internals of those Mazda rotary engines, it’s easy to see how complex they are to keep running, but you cannot help but feel a little bit of sadness that these small-but-powerful engines didn’t make much more of a splash.
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