Dilshan R Jayakody’s Web Log

The Arduino Mini Amplifier is a compact audio system that merges vintage analog and modern digital components. It combines a Philips TDA8425 audio processor and an Arduino Nano , supporting Bluetooth and line-in audio, spectrum analysis, stereo modes, and software-controlled tone adjustment. Finished prototype of the Arduino Mini Amplifier. The Arduino Mini Amplifier is organized into six major subsystems: the audio processor, spectrum analyzer, Bluetooth source, power amplifier, control interface, and power management unit. This modular setup allows each part to operate with minimal interference from the others, making designing and PCB routing easier. The system uses separate paths for analog and digital ground signals (these are called GNDA for analog ground and GNDD for digital ground). Their connections are limited to specific points, which helps prevent unwanted electrical noise from the MCU from reaching the analog audio circuits. The audio section is centered on the T...

For some time, hobbyists have relied on dedicated sound generator ICs, such as the UM3561 , UM3562 to build compact alarm and siren circuits. Unfortunately, this device is becoming increasingly difficult to find in the market. The manufacturer of the chip, United Microelectronics Corporation (UMC), is still around. However, they are no longer producing the UM3561 or UM3562. As part of a fun experiment, I decided to design a replacement circuit using only discrete transistors and passive components. This avoids the need for specialized ICs altogether. The result is a simple yet effective transistor-based siren. It can reproduce the familiar rising and falling alarm effects typically associated with police cars, fire trucks, or ambulances. Finished prototype of the electronic siren. The design philosophy behind this project was straightforward: recreate the functionality of the classic two-timer based siren circuit ( NE556 / NE555 pair), but instead of timers or sound generator ICs, u...

Managing liquid levels in tanks is a common challenge across home, agricultural, and industrial automation systems. Whether dealing with a rooftop water tank or a chemical reservoir in a processing plant, maintaining the correct fluid level is crucial to prevent overflow, avoid dry-run damage to pumps, and reduce unnecessary power consumption. To address this challenge, we have designed a compact and reliable electronic limit switch module. This microcontroller based controller automates fluid level regulation with precision and ease. Prototype build of electronic limit switch module. Traditional fluid level control methods often rely on mechanical float switches and simple relay logic. While effective, these methods can suffer from issues such as bounce noise, relay chattering, and wear over time. This module modernizes this process by integrating microcontroller based debounce filtering, hysteresis, and control on/off delays. To perform its operation, the module utilizes two fl...

Ecowitt2APRS is a new open-source Linux service that I have been working on for the past few weeks. This project is designed to seamlessly integrate weather data from Ecowitt compatible professional weather stations into the global Automatic Packet Reporting System Internet Service (APRS-IS) network, transmitting this information in the standardized format of APRS weather packets. APRS, an amateur radio-based system, facilitates real-time tactical digital communications, covering applications such as GPS position reporting and the dissemination of meteorological data. Ecowitt2APRS addresses a specific need within this ecosystem: providing a lightweight and efficient method for weather stations to contribute to this data stream. Live data view from my Ecowitt weather station on aprs.to. The Ecowitt2APRS service is developed as a minimalist daemon for Linux environments. It ingests live weather data from Ecowitt compatible stations, converts it into the required APRS weather pac...

When it comes to automation and control systems, there's often a need for multiple digitally controlled output terminals with high-voltage handling capabilities. Many existing modules are bulky, expensive, or require numerous additional components to function. To address this gap, I've developed a fully open-source, USB-controlled 24-channel high-voltage driver. This device provides precise, flexible control in a compact and user-friendly package. The project is open hardware, released under the CERN-OHL-W license, ensuring transparency from hardware schematics to firmware code. The driver module communicates via USB using a simple virtual COM port, eliminating the need for special drivers and complex setups. Prototype version of the module. At the core of the system are three TPIC6B595 shift registers, each supplying eight open-drain outputs that can handle up to 50V and sink currents of up to 150mA per channel. These registers are daisy-chained to achieve a total of 24 ...

This blog post discusses the engineering design, construction, and performance evaluation of a 4-element Yagi-Uda antenna specifically optimized for the 2-meter amateur radio band, focusing on the frequency range of 144MHz to 145.5MHz. The project was initiated to establish strong and reliable communication with distant VHF repeaters of the RSSL ( Radio Society of Sri Lanka ), which are located approximately 58km and 96km from my location. The finished antenna, oriented towards the Yatiyantota repeater. The primary objective was to develop a high-gain, directional antenna with a superior front-to-back ratio. This directionality is essential for maximizing signal capture from the desired repeater while minimizing interference and noise from unwanted directions, ultimately improving the SNR and the quality of the communication link. VHF communication at these distances typically relies on line-of-sight propagation, making antenna gain a critical factor in overcoming path loss and ...

This project focuses on a simple yet powerful FM stereo tuner module. The core component of the module is RDA5807M , a single-chip broadcast FM stereo tuner that has gained popularity among designers in recent years due to its high level of integration. This integration significantly reduces the need for external components, simplifying circuit design. The RDA5807M supports a wide FM band, covering frequencies from 50MHz to 115MHz, making it adaptable to global FM standards. Additionally, its use of a low-IF digital architecture streamlines the design process by requiring fewer external parts. The inclusion of an AGC (automatic gain control) feature ensures consistent signal reception, even in environments with fluctuating signal strengths. FM stereo receiver module with seven segment module. The chip's digital stereo decoding capabilities deliver high-quality audio output, providing a rich stereo sound experience. Moreover, the energy efficiency of the RDA5807M makes it suitable...