Dilshan R Jayakody’s Web Log

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...

The 1750Hz tone bursts are often used to trigger repeaters. There are several methods to build 1750Hz tone generators which including TC5082 divider , using MCUs, etc. In this post, I present another 1750Hz tone generator which I built using 74HC4060 high-speed 14-stage binary ripple counter and 7.168MHz crystal. In this design, 74HC4060 is used to drive the crystal and divide its output by 4096. By using 7.168MHz crystal, this circuit produces 1750.0Hz square wave output with a 50% duty cycle. A prototype version of the 1750Hz tone generator. This circuit is extremely simple to build, and I construct my prototype using a breadboard. I tested this generator by connecting its output to my Baofeng UV-5R handheld transceiver and it gives an excellent result. The key motivation to build this generator using 74HC4060 is, because of its common availability. Most of the tone generators which I found on the internet are built using MCUs or by using rare ICs, because of that rea...

This is simple Colpitts oscillator to test commonly available passive crystals which range between 2MHz to 27MHz. This unit must connect to an oscilloscope and/or frequency counter to get the frequency of the crystal. This circuit is designed to work around 9V to 12V DC power source. Both 2SC930 transistors can replace with any high-speed NPN transistor such as 2SC829, 2SC933, etc. Testing 5030kHz FT-243 crystal using a prototype version of crystal tester. In our lab, we use Manhattan-style layout to prototype this crystal tester and it produces highly accurate results with an above-specified frequency range. According to our observations, after 27MHz, the amplitude of the waveform starts to decrease steeply. Schematic and Stripboard wiring layout for this crystal tester is available to download in here .