Dilshan R Jayakody’s Web Log

The primary objective of the Tiny Basic for Arduino project is to replicate that nostalgic C64 style programming environment utilizing modern, low-power MCU platforms. Present-day microcontrollers offer significantly higher processing power and memory capacity than the vintage systems of yesteryear, whilst being available at a fraction of the cost. I envisioned an environment where students and hobbyists alike could experience retro-style computing without the need to source rare, expensive vintage hardware, and completely avoiding any assembly or soldering hassles. By simply connecting a standard, off-the-shelf development board to a PC and launching a serial terminal, one can immediately commence coding in BASIC . Arduino Due: The primary development and testing board. To maintain an authentic and lightweight footprint, the interpreter is built upon the original Tiny Basic language grammar. It accurately parses and executes standard Tiny Basic syntax, making it highly famili...

The TD4 is a famous 4-bit CPU featured in the book How to Build a CPU by Kaoru Tonami . The book focuses on constructing a functional processor entirely from basic 74-series TTL logic ICs. While the book is unfortunately only available in Japanese, a friend from Japan sent me a copy along with a TD4 PCB. I believe the PCB is based on the open-source design files available on BG5DIW's GitHub repository . "How to Build CPU" book and the PCB. Recently, I finally found the time to build and experiment with it. The project took a few months, as I had to translate the book myself to grasp the core concepts. The overall design is simple and elegant, offering a set of 12 instructions and a 16-byte ROM (implemented via DIP switches) for programming. The board operates on 5V and can be powered via USB. Most components were sourced from local shops, though I had to order a few 74HC-series ICs online. Later, I tested the circuit by replacing some 74HC components with 74LS series...

The TDA2005 is a very popular audio amplifier chip that many of us have used for years in car stereos and home DIY amplifiers. While it is mainly built to amplify AF signals, its internal design is actually strong enough to be used for other interesting projects like this DC-to-DC converter. By using the two amplifier channels inside the chip to create a high-frequency signal, we can turn the IC into a power driver that works with a rectifier circuit. Prototype version of TDA2005 DC-to-DC converter. The way this circuit works is quite simple. The TDA2005 stages ( U1A and U1B ) are set up to produce a high-frequency AC signal. This signal goes through 2200µF coupling capacitors and then into a full-bridge rectifier made of 1N5822 Schottky diodes. I chose these specific diodes because they have a very low voltage drop, which helps keep the efficiency high. To keep the TDA2005 stable while it drives this kind of load, I included 1Ω resistors and 0.1µF capacitors as stability network...

I found the ZZRX-40 receiver while going through some old issues of QEX magazine . Designed by Craig Johnson (AA0ZZ) , this is a very simple and easy-to-build 40m direct conversion receiver. Even though it is a simple circuit, it performs quite well for its size. Prototype version of extended ZZRX-40 receiver. For this project, I decided to make my own PCB design because I wanted to use components that I could easily find in our local shops. Since I couldn't find any PCB files online, I drew the schematic in KiCad and designed a custom board. If you are interested in building this, I have shared the Gerber files and KiCad project files here: https://github.com/dilshan/zzrx40-clone . Antenna connector and external VFO headers (JP101 and JP102). The heart of this receiver is the popular NE602 (or SA602 ) mixer chip. This single chip handles both the local oscillator and the product detector, which makes the whole circuit very compact. Although it is designed for the 40-mete...

I recently received a DIY two-tube FM receiver kit from one of my Chinese component suppliers for review. The circuit is elegantly simple, designed around a 1A2 heptode and a 2P2 pentode . The kit includes all the necessary components for the build, featuring a single-sided FR4 PCB with dimensions of 100mm × 100mm. Assembled PCB with tubes. The primary hurdle when starting this project was the complete lack of proper assembly instructions. To assist others, this article documents the exact steps I took to assemble and test the receiver. I have also reverse-engineered the schematic based on the PCB layout; a high-resolution PDF version is available for download here . Top view of the PCB. Bottom view of the PCB. The radio is designed around two main stages to handle frequency conversion and audio amplification: The 1A2 heptode - functions as a super-regenerative detector. The 2P2 pentode acts as the audio power amplifier, which receives the demodulated signal and drives the ...

For an amateur radio operator, having a real-time dashboard is essential for monitoring band conditions and identifying DX opportunities. While several solutions exist, I recently completed a project centered on OpenHamClock , an open-source, web-based successor to Elwood Downey’s (WB0OEW) original HamClock . My goal was to move beyond simply opening a browser tab and instead create a dedicated, always-on kiosk for my workshop/shack. This setup allows me to monitor live DX cluster spots, PSKReporter reception, and satellite X-ray flux in real-time, helping me decide exactly when to jump into a radio session. Prototype build of OpenHamClock kiosk. The heart of this project is a two-component system: a centralized server and a remote kiosk unit. For the server, I utilized a PC equipped with an AMD Ryzen 7 series CPU and 32GB of RAM. While this machine hosts multiple other services, it serves as the perfect, reliable host for the OpenHamClock backend. The installation process is...

This project began with a simple idea: to build a fully functional digital desk clock using only classic CMOS logic ICs that are still readily available in local electronics markets. No microcontrollers, no firmware, no programmable logic - just counters, flip-flops, logic gates, and seven-segment decoders doing exactly what they were designed to do. The result is a 24-hour digital clock powered from a 5V, 1A supply, drawing roughly 200mA, and assembled entirely by hand on a perfboard using point-to-point wiring. Fully assembled CMOS desk clock. At the heart of the clock is a traditional timebase derived from a 32.768kHz crystal oscillator. This frequency is widely used in timekeeping because it can be divided cleanly to exactly 1Hz. A CMOS frequency divider, such as the CD4060 and CD4013 , performs this task, producing a precise one-second pulse that serves as the master clock for the entire system. From this point onward, time is counted purely in hardware, one pulse at a time...