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