MQTT Demystified: Inside the "Post Office" of the IoT World
MQTT is the de facto IoT messaging protocol, designed in 1999 for low-bandwidth, unreliable networks like oil-pipeline monitoring. Unlike HTTP’s request/response model, it uses a lightweight publish/subscribe architecture where devices connect to a central broker, enabling efficient cloud-to-device push without public IPs. Key mechanisms include three QoS levels (at most once, at least once, exactly once), retained messages for late subscribers, Last Will for abnormal disconnects, keep-alive heartbeats, and clean sessions. MQTT 5.0 adds reason codes, shared subscriptions, message expiry, and topic aliases. Compared with HTTP, CoAP, and WebSocket, MQTT offers minimal overhead, flexible reliability, and strong suitability for massive device fleets, low-power sensors, smart homes, industrial IoT, and connected vehicles. The article also provides a runnable Python example using public brokers, helping readers implement their first MQTT publish/subscribe cycle quickly. Readers gain both conceptual understanding and practical starter knowledge.
Operational Amplifier (Op-Amp) Beginner's Guide: From Theory to Practice
This beginner guide explains operational amplifiers from fundamentals to practical use. It covers op-amp types, open-loop operation as a comparator, and negative feedback for linear amplification. Key circuits—voltage follower, non-inverting, and inverting amplifiers—are analyzed using virtual short and virtual open concepts, with gain formulas and common pitfalls. It provides selection guidance, essential DC/AC/bandwidth parameters, and hands-on breadboard lab experiments using LM358. Readers gain the ability to analyze entry-level op-amp circuits, avoid typical mistakes, and build and test basic amplifier circuits with confidence.
![[Open Source] PD65W GaN Charger (ACF), Based on DK8607AD, IP6538-AC-65W, XPM52CDP65](https://img.zeruns.top/blog-en/2026/03/02/WPS%E6%8B%BC%E5%9B%BE0(1)-1772466019.webp)
[Open Source] PD65W GaN Charger (ACF), Based on DK8607AD, IP6538-AC-65W, XPM52CDP65
An open-source 65W PD GaN charger design is presented, combining a DK8607AD-based Active Clamp Flyback (24V/3A) supply with IP6538 or XPM52CDP65 fast-charging DCDC boards. The GaN flyback boards failed during testing, while DCDC boards delivered up to 67.7W with ~95–96% efficiency. Schematics, PCB files, transformer specs, and fabrication materials are provided.
![[Open Source] SC8703-Based Adjustable Buck-Boost DC/DC Power Supply | Voltage & Current Adjustable, PD Fast Charge Input Supported](https://img.zeruns.top/blog-en/2026/02/23/IMG_20260216_180814-1771781704.webp)
[Open Source] SC8703-Based Adjustable Buck-Boost DC/DC Power Supply | Voltage & Current Adjustable, PD Fast Charge Input Supported
An open-source buck-boost DC/DC module based on SC8703 accepts 2.7–36V input and outputs 1.21–36V with up to 10A, adjustable current limit, 600kHz switching, and 95.45% peak efficiency. It includes XT30 and Type-C PD input via CH224Q. Provided files: KiCad project, Gerbers, BOM, stencils, interactive BOM, and 3D models. Proper heatsinking is required; bare-board operation is recommended below 5A.
Open Source 24V3A Flyback Power Supply Based on UC3842, with Transformer Parameter Calculation
An open-source 24V 3A flyback switching power supply design for 85–265VAC input, achieving 87.4% peak efficiency. Based on UC3842 with synchronous rectification, it provides schematics, PCB files, transformer calculations and specifications, and PSIM simulation models. Test data shows 83–87% efficiency, 1.81W no-load consumption, and ripple around 560–730mV. Full-load thermal performance requires heatsinking.
Flyback Power Supply Design: Parameter Calculation, Component Selection & Transformer Winding Guide
This article presents a complete design procedure for a 72W flyback switching power supply (24V/3A) with universal 85-265VAC input. It provides step-by-step calculations for rectifier bridge, input filter, transformer magnetizing inductance and turns, wire selection with skin effect, MOSFET and output diode ratings, output capacitor, and RCD snubber. Key trade-offs such as frequency vs. efficiency, flux density selection, and core AP value are explained. The article also details practical transformer winding, including air gap adjustment and leakage inductance measurement, enabling readers to replicate the design.
WCH CH224K Fast-Charging Protocol Chip: Function Changed but Model Number Remains Unchanged?
WCH’s CH224K datasheet revision (V1F to V2.1) removed single-resistor voltage configuration, disallowing floating CFG pins for 20V requests. This silently breaks existing designs relying on that method. WCH now recommends CH224A, which supports single-resistor mode but requires a 120kΩ resistor for 20V, complicating direct replacement without extra pads. The article questions whether such functional changes warrant a new model number.
Magnetic Components/Magnetic Core Materials & Structures: Analysis, Comparison & Selection Guide
This article provides a systematic guide to magnetic core selection for power electronics, covering key parameters (permeability, saturation, core loss, Curie temperature), comparing materials like ferrite, sendust, permalloy, amorphous and nanocrystalline alloys, and reviewing core structures (EE, PQ, toroidal). It offers engineering recommendations for AC/DC, DC/DC, PFC, and inverter applications, emphasizing frequency matching, loss control, and cost balance. Engineers gain practical reference for choosing cores.
Disassembly and Circuit Design Analysis of ZGRL-80 Photography Light
The article details a teardown of the ZGRL-80 fill light, revealing false advertising: it lacks PD fast charging despite claims, drawing under 10W via Type-C, and its 80W rating is exaggerated with LEDs consuming about 40W. The analysis covers internal circuitry, battery configuration, and thermal imaging, helping readers identify misleading specs and understand budget device limitations.
Open-Source USB 10 Gbps Hub with 2.5 Gbps Ethernet & TF/SD Card Reader (VL822+RTL8156BG+GL3224)
Open-sourcing a USB3.2 expansion dock with Type-C input: 4 USB3.2 Gen2 ports + 2.5G Ethernet + TF/SD card readers, supports PD fast charging for auxil
EG1164 High-Power Synchronous Rectification Boost Module Open Source with 97% Peak Efficiency
EG1164 High-Power Synchronous Rectification Boost Converter Module – Up to 97% Efficiency, Input Voltage 8~50V, Adjustable Output Voltage 8~60V, Maxim
Measured Comparison of Capacitors and Inductors Across Different Brands and Types (D, Q, ESR, X)
Using a Zhongchuang ET4410 LCR bridge, the author measured inductance, capacitance, Q/D, ESR, and reactance of various inductors and capacitors at 100Hz–100kHz. Iron-silicon-aluminum toroidal inductors showed peak Q at 10kHz; SMD inductors performed better at high frequency. Solid capacitors significantly outperformed electrolytics, with Rubycon best among electrolytics. Capacitance dropped after 10kHz for electrolytics, while monolithic capacitors had high low-frequency ESR/reactance. The article provides full data tables and a spreadsheet.
Open-Source Three-Phase Energy Meter: Simplifying Home Electricity Monitoring
An open-source three-phase power meter for home energy monitoring uses three PZEM-004T modules with an ESP32-C3 running ESPHome, uploading voltage, current, power, power factor, and energy data to HomeAssistant over Wi-Fi. It measures 80–260V per phase, up to 100A, with 0.5% accuracy. Design files, firmware, and enclosure models are provided.
Open-Source Smart Electronic Load Based on CH32V307, Embedded Competition Project Open Source
An open-source smart electronic load based on the CH32V307VCT6 microcontroller is presented, developed as a national second-prize entry in the 2023 embedded design competition. It supports constant current, voltage, resistance, and power modes, with 100V/10A/200W ratings. Schematics, PCB files, source code, and reports are freely available for learning and reference.
EG1151 High-Power Synchronous Buck-Boost Power Module (Supports Type-C PD Fast Charging) Open Source
An open-source high-power adjustable buck-boost DC-DC module based on the EG1151 chip is introduced, using fully domestic components. It supports Type-C PD3.1 up to 48V, XT60, and DC5.5 inputs, up to 63V and 20A, with overcurrent and over-temperature protection. Measured peak efficiency is 96.8%, though sustained current is about 18A. Schematics, PCB files, and 3D-printed enclosure models are provided.