Sunday, December 7, 2014

VHF Aircraft radio communications receiver

This is simple radio receiver project which is capable to receive aviation radio voice signals which are transmit between 118MHz to 138MHz in AM (A3E). We got initial idea of this project by reading Sverre Holm’s (LA3ZA) article about "cheap VHF receiver project". Like LA3ZA’s original article this project is also based on Samsung’s KA22429 FM radio receiver IC.

KA22429 is low voltage FM radio receiver system developed by Samsung for portable radio receivers and as described by Holm’s it can push into VHF region by changing few values in its original circuit. In this project we redesign the schematic and PCB with some of those changes and now it can directly tune into aviation band with minimum number of adjustments.

The dimension of PCB of this receiver is 70mm × 45mm and all the components except KA22429 are standard through-hole type.

KA22429 testing setup with 5V PSU and AF power amplifier.

For the optimal results we recommended to use high gain audio power amplifier and good external antenna with this receiver. During prototyping / testing, we drive this system with 5V DC power supply and also connect this receiver to TDA2050 AF power amplifier. At our testing we got very successful results on 124.900MHz (Colombo Airways Center), 119.100MHz (Colombo/ Ratmalana Approach) and 118.100MHz (Colombo/ Ratmalana Tower). The recorded sample on 124.900MHz using this receiver is available in here.

The schematics, PCB design and wiring diagrams of this receiver are available to download at

Wednesday, November 26, 2014

Simple Automatic Car Battery Charger

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 regulator in this system may not need any heatsinks.

This unit is specifically design to charge 12V lead acid car batteries and it is not suitable to use with other battery types. 

Modified schematic of this car battery charger is available to download at

Saturday, November 15, 2014

Homebrew 5 element Yagi antenna for 144MHz

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 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 archive SWR of 1:1.1 - 1:1.2.

Thursday, November 6, 2014

Simple CMOS FSK modem

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 external regulator(s) or level shifters.

Schematic diagram and PCB design patterns of this project are available to download at

Wednesday, October 22, 2014

Optically controlled servo motor

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, standard 3MP or higher grade web cam is sufficient for this system.

prototype assembly of servo driver and servo unit

To demonstrate the exact behavior video is much more suitable but my web cam is used for this project and I don’t have spare web cam to capture the operation of this project. As per our observations servo movement is highly sensitive to the changes of marker object and the movement of the servo motor is also linear and smooth. The propagation time is little bit slow due to serial interface and this can be improved by using high speed I/O interface like USB port.

The source code, servo driver schematic and firmware of this project are available to download at under the terms of the GNU General Public License version 3.0.

Saturday, October 11, 2014

Digitally controlled 2.1 channel analog audio power amplifier

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 project homepage.

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 above content and complete documentation is available to download at

Thursday, September 4, 2014

Trio JR-310 and TX-310 restoration project

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 JR-310, this unit also working with 110V power source.

S2001 final stage vacuum tube and high voltage area of TX-310

I did restoration of above mentioned TX-310 and JR-310 step-by-step and most of the steps are listed in my pages.

Saturday, August 16, 2014

Eddystone EC10 communication receiver restoration and PSU add-in

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 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.

Sunday, August 3, 2014

Panasonic RX-5090T power amplifier repair

Panasonic RX-5090T is quiet old combo box from Matsushita Electric and its most notable feature is powerful three band SW tuner. Recently I got some RX-5090T unit and its problem is distorted audio output.

PCB and mechanical component distribution of Panasonic RX-5090T combo box

After careful examination we identify C128 (100µF / 10V) and C224 (3.3µF 25V) as defective components. In this unit, VR103/203 (20KΩ) potentiometer is also defective and because of that we got some random distortions when we try to change the volume of the receiver. To fix this issue we disassemble the potentiometer and clean it using isopropyl-alcohol (this potentiometer is not available in local market and only option is to clean it and use it again). After these two fixes receiver starts to work again.

Mainboard of Panasonic RX-5090T combo box

Schematic diagram of Panasonic RX-5090T is quiet difficult to find in the web and we share copy of it in here.

Saturday, July 12, 2014

6AS5 and 6N2P vacuum tube base guitar amplifier

This is our first vacuum tube base amplifier project and this project is based on 6AS5 pentode and 6N2P dual triode. Schematic of this project is not designed by us and we got it from web. We got this schematic sometimes ago and now we can't find original site where this schematic appeared first, because of that we host copy of that schematic in here.

Prototype version of 6AS5 and 6N2P guitar amplifier

In original schematic, initial stage of the amplifier is based on 12AX7 high gain tube. During the construction we can't find 12AX7 in local market and because of that we replace 12AX7 with 6N2P. Both 12AX7 and 6N2P had identical characteristics and only major difference is heater configuration. After replacing 12AX7 with 6N2P, both the tubes can drive through single 6.3V filament supply.

6N2P tubes are now commonly available and we use Russian version of 6N2P (6Н2П) for our testing.

We test this amplifier with 4K audio output transformer and it produces excellent results. This amplifier is not suitable for use as Hi-Fi audio amplifier.

Friday, June 27, 2014

Simple RdRand base random number generator library

RDRAND is an instruction to return random number from new Intel CPUs. This is NIST SP 800-90A compliant random number generator and now this instruction is a part of IA-32/IA-64 instruction sets. RdRand instruction is available from 3rd generation Intel Core i5 and Core i7 processors.

RdRandLib is lightweight DLL to generate random numbers based on RdRand instruction. This library contain signal function to generate one or many random numbers and sample codes are available for C/C++, Delphi, Lazarus and C# languages. 

RdRandLib source codes and sample codes are available at Compiled version of DLL is available at page.

Tuesday, June 17, 2014

Analog AC line monitoring box

Analog AC line monitoring box

This is a quick post about our newly constructed AC line monitoring unit. This unit consists with analog AC voltmeter, frequency meter and ammeter. Both voltmeter and frequency meter are 2.5 × 2.5 inch in size and ammeter is 3.5 × 3.5 inch in size. All these panel meters are commonly available in market. Ammeter in this assembly is connected to the mains line through 60A – 5A current transformer and all the other panel meters are coupled to the mains line through 100mA quick blow fuses. Wiring diagram of this unit is illustrated in below.

Wiring diagram of analog AC line monitoring box

Enclosure of this assembly is made with medium density plywood sheets. All the internal mains line of this unit is wired using 2 × 12SWG copper wires.

We construct this unit to monitor the AC line status continuously and also to get some line measurements accurately (from known reference level). In our version of line monitor all the AC line connectors can withstand maximum of 20A because we don't have any idea / plans to do our experiments beyond 20A.

Sunday, June 8, 2014

Digital audio amplifier with PLL synthesized FM radio

This is high quality stereo digital audio amplifier with PLL synthesized FM radio receiver. Some of the high level specifications of this receiver are listed in below:

  • Audio output power: 4W + 4W (with 8ohm speakers)
  • Input sources: FM and 3 external stereo line inputs
  • FM frequency range: 88.00MHz – 108.9MHz
  • Supply voltage: 12V – 15V (2A current source is recommended)
  • Tone control options: Bass, Treble and Loudness control
  • Bass / Treble boost: 14dB
  • Bass / Treble cut: 14dB
  • Station memory: Preset 10 FM radio stations
  • FM tune options: Auto and Manual with 25 kHz steps
Key components of this audio system are ATmega32A - 8bit microcontroller, TT502 (TEA5767) stereo FM radio module, PT2314 audio processor and μPC2002 audio power amplifier. This system is design to work with 12V - 15V (2A) DC power source and KA7632 multi-output regulator is used to manage power requirements to the above mentioned components.

Prototype version of digital audio amplifier

User interface of this system consist with 10 push buttons and 16 × 2 character LCD module. All the analog components of this receiver (including power supply) are controlled by ATmega32A microcontroller.

To get the best audio experience we recommend to couple this system with 8Ω - 8 inches (or higher) full range speaker system. In our prototyping stages we try this system on breadboards and hand-made PCB, and get equivalent results.

This project is an open source hardware project and all the contents are available to download at All the source codes and designs in this project are release under the terms of MIT license.

Sunday, May 18, 2014

Workshop Organizer - inventory controller for home-workshops

Workshop Organizer is light-weight, cross platform inventory controller for home-workshops. This application is specifically design to manage electronic/electrical components at home-workshops, but it can use to manage other areas of workshop including tools, machinery and mechanical components, etc.

To store data, this application use SQLite database system and all the necessary runtime libraries for SQLite is available with the “Workshop Organizer” package. User may not need to download or install separate SQLite database system to use this application. Workshop Organizer default SQLite database consist with more than 600 reference data including list of manufacturers and types.

Workshop Organizer 1.0 on Windows 8.1 operating system

“Workshop Organizer” is a native mode application and user may not need to install any framework to use this application and compiled binaries are available for both Linux and Windows operating systems. 

All the project source codes and compiled binary packages are available at To get more information check Workshop Organizer homepage.

Friday, April 25, 2014

Hi-Fi Audio Power Amplifier for experiments and general use

This is high quality audio power amplifier which we constructed for our audio related experiments. This amplifier is based on NXP’s TDA1521A integrated circuit and it is capable to deliver 2 × 6W audio output power with 20V - 25V asymmetrical power source. The design of this power amplifier is heavily based on the schematic provided in the TDA1521A datasheet. As an addition we incorporate headphone output option to this design.

Connection diagram for TDA1521A Amplifier PCB

PCB which we designed for this amplifier is 55mm × 65mm and it need separate power supply to drive. For optimal results use this AF amplifier with 12V – 20V regulated DC supply and with 4Ω full range speaker pair.

PCB, schematic and wiring diagram of this project is available to download at

Wednesday, April 16, 2014

Audible Morse code to text message converter

Morse View is an open source software project to convert audible Morse codes to text messages. This application is capable to convert Morse codes from wave files or from the audio line/microphone inputs. Conversion from Morse code to text can perform based on amplitude and frequency decomposition of the input audio stream.

Morse View decoding 25 WPM Morse code wave file

We extensively test this application using Morse code files available at ARRL - W1AW code practice page. During the testing we may be able to use this application to decode 5WPM – 40WPM Morse code inputs. As per our test result, after 25WPM, accuracy of the decoder is heavily depends on the quality of the sound card / audio capture device (ADC) and with the system configuration. We test this system with few audio adapters, and out of those adapters both Creative Sound Blaster X-Fi and VIA VT1723 generate more accurate results, especially on 25WPM – 40WPM range.

We test this software with different noise configuration which including ±80% white noise, ±95% pink noise, etc. Under all these conditions decoder may be able to decode the messages with 96.3 – 99.81% accuracy.

This application is developed using Delphi XE5 and complete source code is available to download at Morse View project is distributed under the terms of GNU General Public License Version 3.0.

Sunday, April 6, 2014

300V AC/DC Variable Power Supply

This 300V AC/DC variable PSU is designed for our vacuum-tube, MOSFET and some IGBT related experiments. This PSU consist with 0-300V Variac (variable auto-transformer), 700VA isolation transformer, which is described in previous blog post and high voltage AC-DC converter. Because of the size and weight of these equipment’s we build this PSU as three separate units.

Complete view of 300V AC/DC variable power supply unit.

This PSU is capable to supply 20V - 300V 2.3A (max.) output in either AC or DC form. This PSU use high voltage and because of that, all the proper construction and precautions are necessary to take. Improper wiring or construction may leads to lethal electrical shock and/or fire. If you are not familiar with high-voltage practices do not attempt this project at home.

Schematic of this PSU is available to download at

Thursday, March 27, 2014

Audio / Visual Morse code Generator for Android

This is an Android application to send Morse code messages using tones or flash (light) signals. This application supports for basic Latin alphabet, Arabic numerals and it can transmit messages with specified speed which can vary from 100ms to 500ms.

Main application view

 This application is developed using Delphi XE5 and it supports for Android version 2.3.3 (Gingerbread) to 4.2 (Jelly Beans) except Android version 3.2 (Honeycomb). This application is specifically design for 3.4 inch - 5.0 inch Android smartphones and we tested this application with few Huawei, Samsung and HTC devices.

Audio / Visual Morse code Generator is an open source software project and its source code is available at Compiled package is available to download at This project is distributed under the terms of MIT license.

Delphi Android compiler platform is still evolving and some bug can be expected in this stage. If you found any bugs in this application please let us know via an e-mail.

Saturday, March 22, 2014

Home produced 700VA isolation transformer

This a quick post regarding homemade 300V - 2.3A isolation transformer. This transformer is a part of my ongoing 300V AC/DC variable power supply project and it’s boxed as a separate unit because of its heavy weight and size.

700VA isolation transformer with enclosure

All the parameters of this transformer are calculated using small Python script which I was written sometimes ago. This script support for step-up, step-down or 1:1 power transformer windings and it can execute on any platform where Python 2.7 (or newer version) is supported.

In isolation transformers separation between primary and secondary windings is an important factor. In this transformer I use multiple layers of 3M Scotch Electrical Insulation tape as primary and secondary winding separator. Standard 50mm PVC electrical insulation tape is used to cover secondary winding of this transformer.

Improper connections or construction of this transformer may leads to fire or lethal electrical shock. Because of that reason, make sure to take all the necessary precautions while constructing, testing or using this transformer. Do not try this project if you don’t know what you are doing!

Saturday, March 8, 2014

ATmega169 base 8bit Arithmetic and Logic Unit

ALU (Arithmetic and Logic Unit) is a digital system that performs integer arithmetic and logical operations. In this post we introduce ATmega169 base ALU simulation using Proteus. This is 8bit ALU, and functionally it is similar to other entry level ALUs such as Motorola MC14581, 74LS181, etc. This unit can perform 80 arithmetic and logic operations and all these operations are listed in here.

schematic of ATmega169 base 8bit ALU simulation

Firmware of this ALU is developed using AVR-GCC. While at the development we try to isolate firmware with platform as maximum as possible, because of that, this firmware can be modified to run on top of PIC, 8051 or MSP430 MCUs with minor set of changes.

The Proteus simulation and ATmega169 firmware is available to download at This is an open source software project and all the content are licensed under the terms of MIT license.

Sunday, January 19, 2014

Oscillator Controller for 8bit PIC Microcontrollers

This is oscillator controller for 8bit PIC microcontrollers which is specifically design to debug MCUs and related circuits by without using ICD unit.

This unit consists with low speed oscillator and cycle counter with automatic hold. In current version, oscillator is capable to run in 2 frequency modes and it can count up to 4096 cycles in each run. The number of frequency modes can be extend by adding more capacitors and the upper limit of cycle counter can be increase by adding more 12bit counters (and related circuitries) to the system.

Oscillator waveform in low frequency mode

In current version oscillator can be run in either 66 Hz ~ 70 Hz or 666 Hz ~ 670 Hz (aprox.). This frequency can be adjusted by changing the value of C1 or C2 capacitors (e.g: 0.1MFD can generate 6.39 kHz output signal) OR by replacing R1 with some suitable variable resistor.

In project package we include sample PIC16F84A based project to test with this system. The recommended test attachment is illustrated in below:

Recommended test attachment for PIC16F84A test code

This is open source hardware project and it is licensed under Creative Commons Attribution 4.0 International License. The complete project package is available to download at

Tuesday, January 14, 2014

3.3V Power Supply Unit

Now a days 3.3V PSU is essential for microcontroller, programmable logic devices and for some analog components also (especially with some new ADCs). This is ultra-simple 3.3V power supply unit, which is suitable for above mentioned experiments. This power supply is based on, ON semiconductor’s MC33269T-3.3 LDO regulator and it is capable to deliver 3.3V output with maximum of 800mA current.

External view of 3.3V Power Supply

The PCB design supplied with this article is also compatible with LD1117V33 (also known as LD33V) LDO regulator and it can use with this PCB without any changes. Dimension of the given PCB is 70mm × 35mm and it is design with all through-hole components. Our PCB design for this PSU is available to download at

Maximum input voltage for this module is 20V (DC) for MC33269T-3.3 and 15V (DC) for LD1117V33 (or LD33V). In our unit we use 230V – 9V (1A) step down transformer as AC input for this unit.

Friday, January 10, 2014

Extended Run dialog box for Windows

When it comes to Windows operating systems I highly addicted to the "Run" dialog box. Technically, to me it functions like a single-line command line interface. From Windows 95 to Windows 8.1, layout and the functionalists of "Run" dialog box is quiet identical.

To extend the functionalists of "Run" dialog box we did some project call "QRun". The main purpose of QRun is to provide more convenient user-interface to existing Windows "Run" dialog box.

QRun window with Action menu entries
The key feature of QRun is its menu driven command and resource selector. This menu driven interface help end user to perform actions by without memorizing commands and/or parameters. Another feature of QRun is its macro commands. Using this feature end user can create custom actions for run dialog box.

Other than above features QRun also had inbuilt support for win-bash. Because of this feature end user may be able to run GNU bash related commands directly from the run dialog box. 

Once installed in a system, user can open QRun by navigating over start menu/screen OR by pressing Shift + WinKey + R key combinations.

QRun is an open source free software project and it is distributed under the terms of MIT license. Latest version of QRun is available to download at Details about manual installations, compiling and configuring of QRun are available at