Dilshan R Jayakody’s Web Log

WebRTC is a web technology to enable peer to peer communication in real-time. It mainly uses to create video conferencing and chat applications using web browsers. In this post, we describe how to enable this technology in QtWebEngine on Raspberry Pi 3 platform. QtWebEngine is an embedded browser component which comes with the Qt framework . This component is based on Google Chromium browser and it supports most of the Chromium features including WebRTC. In PC, WebRTC applications run smoothly on QtWebEngine component. But in Raspberry Pi platform situation is different and none of the WebRTC application is work with the QtWebEngine. The only thing which we can see is a black box in an HTML5 video tag area. At the time of writing this problem exists in Qt version 5.6, 5.7 and 5.8.

Due to the advancement of audio technologies reel to reel audio tapes are now classified as a rare item. The biggest problem with the reel to reel tapes is a fungus . The fungus is developed on old unused tapes due to humidity exposure. Also, another problem with old tapes is that the lubrication on the surface of the tape starts to deteriorate and tape starts to stick to itself, and this leads tape to break during the playback. Most of them that have Fungus can be fixed by using a tape cleaner. But these days reel to reel tape cleaners are not available to buy and because of that, we decided to build simple tape cleaner by using parts of old reel to reel tape players. The core component of this player is an induction motor which we got from an old reel to reel player. The motor which we used in this project is the Sony HC-134. HC-134 is 100V single-phase, capacitor run, induction motor with 1500 - 1800 RPM. Recommended auxiliary winding capacitor for this motor is 1.5μF. To delive...

HiFi Studio 1 is portable boombox manufactured by Telefunken in around 1979. This player consists of 4 band radio (with LW, MW, SW, and FM), cassette player/recorder and with 2 × 30W audio power amplifier. Restored HiFi Studio 1 This unit is designed using both ICs and transistors. The receiver of this unit is built around TDA1047, TBA570 and BA1320 ICs. Tape player/recorder is mainly build using NPN transistors and special Telefunken IC and 4066 ICs are used to get Telefunken's proprietary HIGH COM tape noise reduction feature. The power amplifier of this boombox is transistor based and it uses a pair of TIP130 and TIP135 transistors in its final stage.

TC-252 is 3-speed reel to reel player manufactured by Sony in around 1970 – 1972. This is transistor based tape player with 4W × 2 audio output power, sound-on-sound, and sound-with-sound recording features. The TC-252 which we got to restore had many problems. The major problem is someone alters the circuit in that recorder and attach LA4440 power amplifier into the circuit. Apart from that, the motor speed of that recorder also starts to decrease after 10min of continues playback. Other than above two major problems it had some mechanical problems in playback position and all the potentiometers in the front panel are damaged beyond repair. TC-252 main PCB after restoration. As a first step of the restoration, we remove the LA4440 module attached into that recorder and rewire the player with original wiring layouts. After rewiring we check all the transistors in that player and find out that the couple of 2SC634 transistors are damaged in that player. Because 2SC634 is not a...

Pioneer PL-250 is direct drive auto-return turntable with the s-shaped tonearm. This turntable is manufactured by Pioneer in around 1979 - 1982. The PL-250 which we got had many electronic and mechanical issues. The main electronic problem in this unit is it's varying speed. The speed controller of this turntable is based on PA2004 and PA2005 ICs. After checking each an every electronic component in speed controller PCB, we figure out that the problem is in the " Pitch Control " potentiometer (VR1) of this unit. After replacing VR1 with 5K (log) potentiometer, the speed problem got resolved and the motor starts to spin with correct speed(s). Servo motor and speed control assembly of Pioneer PL-250 turntable. The turntable which we got comes with original Pioneer cartridge with "broken" stylus. We test several cartridges with this player including cheap US $ 3.00 cartridges (which are available on eBay), Audio Technica AT-91 and Audio Technica AT-95E ...

This quick post is to introduce " HTML5 Mandelbrot Generator ", which is a simple JavaScript application to generate Mandelbrot set and Julia set fractals in HTML5 compliant web browsers. This application is derived from Mandel source code (which is available at http://www.cylog.org ) and it covers most of the features available in that original application. The online version of this HTML5 Mandelbrot Generator is available at https://dilshan.github.io/mandelbrot-js . Few fractals generated with "HTML5 Mandelbrot Generator" are shown below: Mandelbrot and Julia set fractals generated from "HTML5 Mandelbrot Generator". All the source code of this application are available to download at https://github.com/dilshan/mandelbrot-js under the terms of MIT Licenses .

This is a quick post to showcase 100W 4 channel AF dummy load which we build to test the output stages of audio power amplifiers. This dummy load use 4, 8Ω 100W wire wound resistors which are available on eBay . In this unit, all 4 resistors are mounted on 170mm × 40mm × 60mm high gauge aluminum heat sink. A prototype version of the 100W AF dummy load. It costs LKR1200 to build this unit and the most expensive component in this unit are wire wound resistors. At the time of writing these 100W resistor packs are available on eBay for USD $6.00.