Dilshan R Jayakody’s Web Log

This is modified version of commonly available automatic car battery charger system. I obtain original layout of this charger from one of the commercially available Chinese car battery charger and modified some of the sections of original schematic to improve the performance and stability of the system. This charger is mainly based on LM311 comparator and 2 ×12V 4A transformer. Final view of automatic car battery charger All the components of this car battery charger are commonly available in the market. Ammeter in this system must be withstand for minimum of 8A current. Low cost ammeter can also be used with suitable shunt. For the relay it is highly advisable to use some high quality unit. During our prototyping we mainly use 12V Omron and Panasonic realys with this system. At the test stages we observe that some of the cheap relays may start to oscillate heavily with this system. Automatic car battery charger finished prototype Under normal conditions TIP142 and 7805...

This is 5 element Yagi-Uda antenna for 144MHz amateur radio transmissions and receiving. This antenna is design using commonly available TV antenna parts. The CAD drawing of this antenna is available to download in my QSL.net pages and all the measurements in that diagram are in mm (millimeters). The total boom length of this antenna is around 1500mm and maximum span is 1016.10mm. 3D visualization of 5 element Yagi antenna After the construction I test this antenna on 145.625MHz and got SWR of 1:1.3 with quiet lengthy, standard 50Ω RG-58 cable. With high quality shorter cable I achieve SWR of 1:1.1 - 1:1.2.

This project is about 4046 PLL base simple FSK modem. Under given configuration this modem send digital signals over two frequencies and which is switching around 378kHz and 226kHz. In this system, modulator uses VCO of 4046, and demodulator is based on close loop mode of 4046 phase comparator and external LPF assembly. This FSK modem is specifically design to transfer digital signals over mixed signal lines and it can directly use with any slow digital interfaces like UARTs. This system operates reliably under 10kHz range and we test it with standard TTL inputs. 1kHz Input signal and demodulated signal 1kHz Input signal and modulated signal The given PCB of this system is based on SMD components but it can also construct using standard through-hole components. During our prototyping we test this system with ATmega series microcontrollers and TTL signals sources. Because of 4046 CMOS implementation this unit can operate in between 3V to 12V by without using any extern...

This is demonstration project to control servo motor movement using physical marker and normal video camera. In this project video camera capture the movements of marker and calculate rotation angle based on that. This calculated rotation angle is feed to the servo through small MCU based interfacing unit. In this project video processing and tracking is performed using ARToolkit and controlling of servo is carried out using PIC16F628A microcontroller. RS232 interface is use to communicate between PC and microcontroller. Interfaces in optical servo controlling system This application detects movement of marker on Z axis (yaw) and transforms it into another numerical scale to manipulate the servo motor. Processing application is written using Visual C++ and configured to work on Windows operating system(s). The marker used for this application is needed to be a " square with some symbol " and user can train this system for any compatible marker. As per our tests, st...

This article introduces high quality digitally controlled 2.1 channel analog audio power amplifier system. This project is mainly based on TDA7377 AF power amplifier and PIC18F452 8bit microcontroller. Basic features of this receiver are 2 × 6W + 20W audio output power, ±14dB bass and treble controls, fully configurable +35dB bass booster for sub-woofer and satellite speakers and loudness switch. This system use commonly available electronic components and all the integrated circuits are in DIL packages. This amplifier consists with few UI elements such as 2 push buttons and 1 rotary encoder. All the menu navigation can perform through rotary encoder. Prototype version of 2.1 channel audio power amplifier project Entire amplifier can build on 147mm × 80mm PCB and all the PCB design files are available to download at google drive . This is an open hardware project and all the firmware source codes, design files are covered with Mozilla Public License version 2.0 . All the ab...

I got Trio ( now Kenwood ) JR-310 and TX-310 SSB receiver and transmitter pair recently. When it comes to me both receiver and transmitter are in very bad shape and most of the PCBs and chassis are covered with dust and some of the components are very badly damaged. After examining both the chassis I decided to repair both units because of its vintage value (and also I like to try some tube base SSB receiver and transmitter pair). Trio JR-310 is AM, SSB and CW mode HF receiver. This receiver has 3.5, 7, 14, 21, 25 and 50MHz operating bands and sensitivity is around 1µV. This receiver consists with 6 vacuum tubes, 5 transistors and 19 diodes. JR-310 which I restored is working with 110V and total power consumption is around 70W. Bottom view of restored JR-310 receiver TX-310 is 20W SSB transmitter and designed to match with JR-310 receiver. It is capable of LSB, USB, AM and CW transmissions in HF bands. This unit consists with 10 vacuum tubes, 5 transistors and 9 diodes. Like ...

Recently I got vintage Eddystone EC10 MK1 communication receiver from friend of mine and it is completely dead when it comes to me. EC10 MK1 is one of Eddystone's very early solid state communications receivers and it use 10 PNP Germanium transistors. This receiver cover 550 kHz to 30 MHz and come up with BFO for CW and SSB receptions. Restored EC10 MK1 HF communication receiver The main problems which I noticed in my EC10 is corroded wires, components and PCB. I did restoration step-by-step and most of the steps are listed in my qsl.net page . Other than repairing, this article covers details of power supply which I integrated into EC10 communication receiver. The schematics and photographs are available at the same article . After repairing and above changes EC10 starts to work again and with some external antenna is performs quiet well. Most of the times I use this receiver to listen to 40m 4S7RS net on 7060kHz.