Zeruns's Blog - English Site
MQTT Demystified: Inside the "Post Office" of the IoT World
Internet of Things / Embedded

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.

Published on 2026-07-23
Operational Amplifier (Op-Amp) Beginner's Guide: From Theory to Practice
Electronics / Circuits

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.

Published on 2026-04-30
Open Source 24V3A Flyback Power Supply Based on UC3842, with Transformer Parameter Calculation
Electronics / Circuits

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.

Published on 2025-10-13
Flyback Power Supply Design: Parameter Calculation, Component Selection & Transformer Winding Guide
Electronics / Circuits

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.

Published on 2025-10-13
Open-Source USB 10 Gbps Hub with 2.5 Gbps Ethernet & TF/SD Card Reader (VL822+RTL8156BG+GL3224)
Electronics / Circuits

Open-Source USB 10 Gbps Hub with 2.5 Gbps Ethernet & TF/SD Card Reader (VL822+RTL8156BG+GL3224)

An open-source USB-C dock integrates four 10Gbps USB-A ports, 2.5G Ethernet, and TF/SD readers using VL160, VL822, RTL8156BG, GL3224. It accepts 4-20V input, buck-boosts to 5.1V with up to 9.5A, supporting PD fast charging. Tests show USB read/write 969.65/912.65 MB/s, Ethernet 2089/2497 Mbps, card read 93.04 MB/s, efficiency up to 91.79%. Schematics, PCB files, and replication notes are provided.

Published on 2025-04-29
Measured Comparison of Capacitors and Inductors Across Different Brands and Types (D, Q, ESR, X)
Electronics / Circuits

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.

Published on 2025-02-15
Open-Source Smart Electronic Load Based on CH32V307, Embedded Competition Project Open Source
Electronics / Circuits

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.

Published on 2025-02-06

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