The Joule Thief circuit is a simple, self-oscillating voltage booster that allows low-voltage sources, like a nearly depleted 1.5V battery, to power devices requiring higher voltages. It uses a single transistor, a resistor, and a toroidal transformer with a feedback winding. When the circuit is energized, the transistor initially conducts, allowing current to flow through the primary winding of the transformer. This builds a magnetic field. As the current increases, the voltage across the resistor also increases, eventually turning the transistor off. The collapsing magnetic field in the transformer induces a voltage in the secondary winding, which, combined with the remaining battery voltage, creates a high voltage pulse suitable for driving an LED or other small load. The feedback winding further reinforces this process, ensuring oscillation and efficient energy extraction from the battery.
Ken Shirriff's blog post details the surprisingly complex circuitry the Pentium CPU uses for multiplication by three. Instead of simply adding a number to itself twice (A + A + A), the Pentium employs a Booth recoding optimization followed by a Wallace tree of carry-save adders and a final carry-lookahead adder. This approach, while requiring more transistors, allows for faster multiplication compared to repeated addition, particularly with larger numbers. Shirriff reverse-engineered this process by analyzing die photos and tracing the logic gates involved, showcasing the intricate optimizations employed in seemingly simple arithmetic operations within the Pentium.
Hacker News users discussed the complexity of the Pentium's multiply-by-three circuit, with several expressing surprise at its intricacy. Some questioned the necessity of such a specialized circuit, suggesting simpler alternatives like shifting and adding. Others highlighted the potential performance gains achieved by this dedicated hardware, especially in the context of the Pentium's era. A few commenters delved into the historical context of Booth's multiplication algorithm and its potential relation to the circuit's design. The discussion also touched on the challenges of reverse-engineering hardware and the insights gained from such endeavors. Some users appreciated the detailed analysis presented in the article, while others found the explanation lacking in certain aspects.
This post discusses the nuances of ground planes and copper pours in PCB design, emphasizing that they are not automatically equivalent. While both involve areas of copper, a ground plane is a specifically designated layer for current return paths, offering predictable impedance and reducing EMI. Copper pours, on the other hand, can be connected to any net and are often used for thermal management or simple connectivity. Blindly connecting pours to ground without understanding their impact can negatively affect signal integrity, creating unintended ground loops and compromising circuit performance. The author advises careful consideration of the desired function (grounding vs. thermal relief) before connecting a copper pour, potentially using distinct nets for each purpose and strategically stitching them together only where necessary.
Hacker News users generally praised the article for its clarity and practical advice on PCB design, particularly regarding ground planes. Several commenters shared their own experiences and anecdotes reinforcing the author's points about the importance of proper grounding for signal integrity and noise reduction. Some discussed specific techniques like using stitching vias and the benefits of a solid ground plane. A few users mentioned the software they use for PCB design and simulation, referencing tools like KiCad and LTspice. Others debated the nuances of ground plane design in different frequency regimes, highlighting the complexities involved in high-speed circuits. One commenter appreciated the author's focus on practical advice over theoretical explanations, emphasizing the value of the article for hobbyists and beginners.
The article argues against blindly using 100nF decoupling capacitors, advocating for a more nuanced approach based on the specific circuit's needs. It explains that decoupling capacitors counteract the inductance of power supply traces, providing a local reservoir of charge for instantaneous current demands. The optimal capacitance value depends on the frequency and magnitude of these demands. While 100nF might be adequate for lower-frequency circuits, higher-speed designs often require a combination of capacitor values targeting different frequency ranges. The article emphasizes using a variety of capacitor sizes, including smaller, high-frequency capacitors placed close to the power pins of integrated circuits to effectively suppress high-frequency noise and ensure stable operation. Ultimately, effective decoupling requires understanding the circuit's characteristics and choosing capacitor values accordingly, rather than relying on a "one-size-fits-all" solution.
Hacker News users discussing the article about decoupling capacitors generally agree with the author's premise that blindly using 100nF capacitors is insufficient. Several commenters share their own experiences and best practices, emphasizing the importance of considering the specific frequency range of noise and choosing capacitors accordingly. Some suggest using a combination of capacitor values to target different frequency bands, while others recommend simulating the circuit to determine the optimal values. There's also discussion around the importance of capacitor placement and the use of ferrite beads for additional filtering. Several users highlight the practical limitations of ideal circuit design and the need to balance performance with cost and complexity. Finally, some commenters point out the article's minor inaccuracies or offer alternative explanations for certain phenomena.
Eki Bright argues for building your own internet router using commodity hardware and open-source software like OpenWrt. He highlights the benefits of increased control over network configuration, enhanced privacy by avoiding data collection from commercial routers, potential cost savings over time, and the opportunity to learn valuable networking skills. While acknowledging the higher initial time investment and technical knowledge required compared to using a pre-built router, Bright emphasizes the flexibility and power DIY routing offers for tailoring your network to your specific needs, especially for advanced users or those with privacy concerns.
HN users generally praised the author's ingenuity and the project's potential. Some questioned the practicality and cost-effectiveness of DIY routing compared to readily available solutions like Starlink or existing cellular networks, especially given the complexity and ongoing maintenance required. A few commenters pointed out potential regulatory hurdles, particularly regarding spectrum usage. Others expressed interest in the mesh networking aspects and the possibility of community-owned and operated networks. The discussion also touched upon the limitations of existing rural internet options, fueling the interest in alternative approaches like the one presented. Several users shared their own experiences with similar projects and offered technical advice, suggesting improvements and alternative technologies.
Ken Shirriff reverse-engineered interesting BiCMOS circuits within the Intel Pentium processor, specifically focusing on the clock driver and the bus transceiver. He discovered a clever BiCMOS clock driver design that utilizes both bipolar and CMOS transistors to achieve high speed and low power consumption. This driver employs a push-pull output stage with bipolar transistors for fast switching and CMOS transistors for level shifting. Shirriff also analyzed the Pentium's bus transceiver, revealing a BiCMOS circuit designed for bidirectional communication with external memory. This transceiver leverages the benefits of both technologies to achieve both high speed and strong drive capability. Overall, the analysis showcases the sophisticated circuit design techniques employed in the Pentium to balance performance and power efficiency.
HN commenters generally praised the article for its detailed analysis and clear explanations of complex circuitry. Several appreciated the author's approach of combining visual inspection with simulations to understand the chip's functionality. Some pointed out the rarity and value of such in-depth reverse-engineering work, particularly on older hardware. A few commenters with relevant experience added further insights, discussing topics like the challenges of delayering chips and the evolution of circuit design techniques. One commenter shared a similar decapping endeavor revealing the construction of a different Intel chip. Overall, the discussion expressed admiration for the technical skill and dedication involved in this type of reverse-engineering project.
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https://news.ycombinator.com/item?id=43235671
Hacker News users discuss the Joule Thief circuit's simplicity and cleverness, highlighting its ability to extract power from nearly depleted batteries. Some debate the origin of the name, suggesting it's not about stealing energy but efficiently using what's available. Several commenters note the circuit's educational value for understanding inductors, transformers, and oscillators. Practical applications are also mentioned, including using Joule Thieves to power LEDs and as voltage boosters. There's a cautionary note about potential hazards like high-voltage spikes and flickering LEDs, depending on the implementation. Finally, some commenters offer variations on the circuit, such as using MOSFETs instead of bipolar transistors, and discuss its limitations with different battery chemistries.
The Hacker News post titled "Understand the Joule Thief Circuit" linking to an Electronics Stack Exchange question about the same topic has several comments discussing various aspects of the circuit and its functionality.
Several commenters focus on correcting or clarifying details about the Joule Thief's operation. One commenter points out that the circuit doesn't actually "steal" joules but rather makes use of energy otherwise wasted in a nearly depleted battery. They emphasize that the voltage is boosted, not the current, allowing the LED to operate at a higher voltage than the battery can directly provide. Another commenter builds upon this by explaining how the circuit functions as a self-oscillating boost converter, using the transformer's feedback to regulate the switching.
Another thread of discussion revolves around the efficiency and practicality of Joule Thief circuits. One commenter questions the circuit's actual efficiency, suggesting that the rapid switching might lead to significant losses in the components. Another commenter responds, agreeing about potential inefficiencies, but acknowledges that the simplicity of the design makes it useful for extracting the last bit of energy from a battery in low-power applications. This commenter further suggests a potential improvement using a CMOS 555 timer for potentially higher efficiency.
A few comments delve into more technical aspects of the circuit. One explains how the circuit exploits the transformer's behavior during the "flyback" period, where the collapsing magnetic field induces a higher voltage. Another discusses the role of the feedback winding in controlling the transistor's switching, clarifying why it is wound in the opposite direction to the primary winding.
Other comments offer practical advice, such as selecting appropriate components, like the transistor and the ferrite core for the transformer. One comment specifically cautions against using higher voltages, emphasizing the circuit's design for single-cell batteries, and highlighting safety concerns.
Finally, some comments discuss alternative circuits and applications. One user mentions using a similar circuit to power a white LED from a single AA battery and discusses component selection based on desired brightness.
Overall, the comments provide a wide range of perspectives, from basic explanations of the circuit's function to deeper discussions about its efficiency and limitations, as well as practical tips and alternative approaches.