Monday, November 21, 2016

HTML5 Mandelbrot Generator

This quick post is to introduce "HTML5 Mandelbrot Generator", which is simple JavaScript application to generate Mandelbrot set and Julia set fractals in HTML5 complaint web browsers. This application is derived from Mandel source code (which is available at and it covers most of the features available in that original application.

Online version of this HTML5 Mandelbrot Generator is available at Few fractals generated with "HTML5 Mandelbrot Generator" are shown in below:

Mandelbrot and Julia set fractals generated from "HTML5 Mandelbrot Generator".

All the source code of this application are available to download at under the terms of MIT Licenses.

Monday, November 7, 2016

100W AF dummy load

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 in eBay. In this unit all 4 resistors are mounted on 170mm × 40mm × 60mm high gauge aluminum heat sink.

Prototype version of 100W AF dummy load.

It costs LKR1200 to build this unit and most expensive component in this unit are wire wound resistors. At the time of writing this 100W resistor packs are available in eBay for USD $6.00.

Monday, October 31, 2016

Extending the frequency range of Pioneer TX-7700 tuner

TX-7700 is AM/FM stereo tuner manufactured by Pioneer in around 1975 - 1980. This is basic tuner system which is specifically designed for "rack style" stereo systems. Compare with other tuner systems this tuner is not very popular and very limited information are available in the internet about this model.

This tuner is mainly build around HA1138 AM radio receiver, HA1156 stereo decoder and PA3001 (HA11225) FM IF amplifier IC.

The TX-7700 which I got is manufactured for Japan and because of that it is designed to work with 100V AC and frequency range is limited to 76MHz to 90MHz. In this quick post we demonstrate how to tune this stereo receiver to 88MHz to 108MHz by without modifying the circuit(s) of tuner.

In this tuner the main component which need to adjust is 5 turn inductor located in FM front end circuit (refer A in below photograph). The frequency range of the tuner can be adjusted by changing the spacings of this inductor. If tuning is getting difficult, slightly adjust the trimmer capacitor in that module (marked as B in same photograph).

FM front end components to adjust.

After carefully adjusting the inductor and trimmer capacitor we were able to tune TX-7700 into 88MHz -108MHz frequency range. Once the receiver is desired frequency range the clarity of the reception can adjust by tuning the compression trimmers located in tuning capacitor (refer C and D in below photograph).

Trimmer capacitors of FM tuner stage.

This method can be used to tune any analog (FM) tuner which have identical design to TX-7700.

Saturday, September 24, 2016

μPC1237 based 2 channel speaker protector

When working with expensive speaker system, speaker protector is an essential item to avoid any damages to speakers. In this project we build low cost speaker protector by using NEC's μPC1237 IC. The circuit in this project is based on μPC1237 datasheet and it is specifically modified to work with 24V AC power source and with 24V relay.

Prototype version of μPC1237 - 2 channel speaker protector system.

PCB design of this project is limit to 90mm × 43mm and based on through hole components. Depending on supplied voltage and relay, value of R7 resistor is need to be change. The specified value in schematic is for 24V AC power source and for Omron 24V G2R-2 relay. Start-up delay of this unit can be adjust by changing the values of R5 and C5.

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