Dilshan R Jayakody’s Web Log

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.

TX-7700 is AM/FM stereo tuner manufactured by Pioneer in around 1975 - 1980. This is a 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 is available on the internet about this model. This tuner is mainly built 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 the tuner. In this tuner, the main component which needs 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 dif...

When working with an expensive speaker system, speaker protector is an essential item to avoid any damages to speakers. In this project, we build a 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 the 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 the supplied voltage and relay, the value of R7 resistor is needed to be changed. The specified value in the schematic is for 24V AC power source and for Omron 24V G2R-2 relay. Start-up delay of this unit can be adjusted by changing the values of R5 and C5. Schematic and PCB design files of this project are available to download at google drive .

CoCA "Emerge + Tech" - Musical plants is an electronics, software and plants base exhibit we developed for Cinnamon Colomboscope 2016 exhibition. This installation will feature a touch-sensitive sensor that will generate a soothing sound from each plant. By interacting with individual plants, the audience can create musical compositions. The sensor unit of this project consists of 14 high sensitive, configurable level detectors and USB interface. In this sensor unit, we use Samsung's KA2284 as an amplifier, level detector, and PIC18F4550 8-bit MCU as data multiplexer and USB I/O controller. PC817 optoisolators are used to interface between analog front-end and digital data processor. In this design, both analog and digital circuits are physically and electronically isolated to minimize the noises and interferences. In this design, we use KA2284 because it is commonly available in the local market (in Sri Lanka) and costs less than 0.1 USD. To reduce the interfer...

TC-500 is 4 track stereo reel to reel player which is built around 1960 - 1970 by Sony Corporation. This is vacuum tube base reel to reel player with 2 × 3W audio output power. TC-500 is dual speed (3¾ and 7½ ips) tape recorder and it support reels up to 7 inches (18cm). Amplifier stage of this tape recorder is built around 12AX7, 6AU6 and 6AQ5 vacuum tubes and the 12BH7 tube is used in biasing oscillator. Other than above tubes, 6CA4 is used in PSU for rectification. Restored Sony TC-500 reel to reel tape recorder. Recently we got a chance to restore TC-500 reel to reel player which we got from our friend. The player which we got is heavily damaged and we spend nearly 2½ months to restore this player. In the first stage of restoration, we disassemble mechanical parts of this player and clean everything. In this player capstan idler wheel and take-up, idler wheel is damaged beyond repair and we reconstruct those wheels using rubber sheets.

HD-1410 is quite popular iambic keyer which is manufactured around the 1970s by Heathkit . The original HD-1410 keyer is designed using 5 commonly available 74LS series TTL ICs and 8 transistors. Other than iambic operation it has an option to adjust sidetone frequency and support for (external) single-paddle key unit. In this project, we redesign the original HD-1410 electronic keyer with today's commonly available components. In this new design, the key components which we replace are transistors, diodes, and power supply section of the original HD-1410 circuit. Most of the NPN transistors in original design are replaced with KSP42 and KSP10 transistors, and all the PNP transistors are replaced with KSP92 transistors. To keep everything simple we also use the same TTL chip-set with this new design. PCB of modified Heathkit HD-1410 electronic keyer. Tested PCB layout for this new keyer is available in the project archive and this PCB layout is based on standard through-...

This is simple Colpitts oscillator to test commonly available passive crystals which range between 2MHz to 27MHz. This unit must connect to an oscilloscope and/or frequency counter to get the frequency of the crystal. This circuit is designed to work around 9V to 12V DC power source. Both 2SC930 transistors can replace with any high-speed NPN transistor such as 2SC829, 2SC933, etc. Testing 5030kHz FT-243 crystal using a prototype version of crystal tester. In our lab, we use Manhattan-style layout to prototype this crystal tester and it produces highly accurate results with an above-specified frequency range. According to our observations, after 27MHz, the amplitude of the waveform starts to decrease steeply. Schematic and Stripboard wiring layout for this crystal tester is available to download in here .

Curve tracer is an electronic test instrument to analyze the characteristics of transistors and other discrete semiconductors. In this post we construct USB base curve tracer to analyze properties of NPN transistors. This curve tracer is build around Microchip's PIC18F4550 MCU and it use simple Windows based GUI application to plot captured data of a transistor. In this design PIC18F4550 MCU is used to establish USB connectivity, perform voltage readings and control current/voltage flow into the test subject. To minimize the cost and to make it simple, we use R2R ladder circuit to generate discrete collector-emitter voltage levels for the transistor on test. In each scan session collector-emitter voltage level get increase from 0V to 7.5V in 256 steps. In this design, "tracer" scans the transistor for 7 base current levels which are in between 7µA to 60µA. In viewer application collector-emitter voltage levels are plotted on x-axis and collector current is plotted o...

This is an automatic "monitor brightness controller" based on environmental light conditions. This system uses a USB port base sensor unit to measure the light level and control monitor brightness accordingly. We design this system to reduce eye stress by matching the monitor brightness with environmental lighting. The sensor unit of this system is built around PIC18F2550 8-bit microcontroller. To measure the light level we use LDR with MCU's inbuilt ADC. The control software of this unit is design to work with Microsoft Windows operating systems and it uses Windows API's DDC/CI related functions to control the monitors/display devices. The firmware of USB sensor use 50-point boxcar filter to get the average readout from the ADC and that value is passed to PC over USB HID interface. Thanks to this HID interface this system may not need any special device driver, and it can use in any compatible PC with a minimum amount of configuration changes. A prototype v...

In this post, we introduce simple and flexible, regulated low voltage power supply unit. This power supply has provision for 4 outputs such as 1.5V, 1.8V, 2.5V and 3.3V. We mainly build this low voltage power supply unit to test (and power-up) low voltage MCUs, CPLDs, and radio receivers. For this power supply, we choose 1.8V, 2.5V and 3.3V to get it compatible with most of the LVTTL/LVCMOS devices. Other than that, we include 1.5V because there are several analog ICs are available for that voltage level. This power supply unit is based on LM1117/AMS1117 voltage regulator series and for this design, we use AMS1117-1.5, AMS111-1.8, AMS1117-2.5, and AMS1117-3.3 fixed voltage regulators. Except to above regulators, this board can be used with AMS1117-2.85 and AMS1117-5.0 regulators. Internal view of the low voltage power supply unit. In our prototype, we use center-tapped 6V (1A) step down transformer with this power supply unit. All the wiring diagrams to transformer and rotary...

This is quick (and final) post regarding our Mullard 3-3 audio amplifier project. In the last few months, we got several e-mails regarding this project and most of the people are asking for modified schematic related to this project . The schematic of our amplifier is available to download in here . Please note that this schematic is heavily based on the original Mullard 3-3 amplifier design and the main component which we replace in that original schematic is its tube base power supply unit. As a final step of this project, we construct a wooden enclosure for that amplifier and attached it to 10 inch (8Ω) full range speaker. High-resolution photographs of our amplifier are available in here . Final view of Mullard 3-3 audio power amplifier As a conclusion, this Mullard 3-3 audio power amplifier is a high-quality low power tube amplifier with minimum complexity. We really impressed with its audio quality and overall performance.

Star test is the most recommended method to test and collimate telescopes . To do a " star test " we need to aim and track telescope with real star and most of the times this is quite difficult to do because of the fast movement of stars and bad sky conditions. Another problem with the real star is air turbulence and some times this effect may lead to false conclusions. However artificial star is an excellent alternative for " real star test " and in this post, we introduce easy to build "artificial star unit" to test and collimate telescopes. This unit is based on commonly available electronic components and it can operate with a 9V battery. At the time of writing this unit can build around LKR 1000.00 (Approximately 7.00 - 8.00 USD). In this given design, we use NE555 timer IC to generate PWM output to LED and this allows us to control the intensity of the artificial star. In our prototype we use high-bright 3mm white LED as our light source. Apa...

This is a second article related to Mullard 3-3 Amplifier Project and in this article, we introduce HT transformer and HT power supply related to this amplifier. As mentioned in the previous post, the power supply unit of this tube amplifier is constructed using 400V 5A bridge rectifier, 220µF (400V) and 82µF (400V) electrolytic capacitors. Homebrew HT transformer and PSU The most vital component of this power supply is the HT transformer and due to limited availability, we construct this transformer by ourselves. We construct this transformer to obtain the following voltages and primary winding is design for 230V AC mains lines.

This is a very simple electronic doorbell circuit which is specifically designed to interface with commonly available access control systems. This circuit is designed around an NE555 timer IC and LM386 audio power amplifier IC. Because most of the access control systems use 12V power supplies this doorbell is also designed to work with 9V to 15V DC power source. Final view of our doorbell project prototype. We test this doorbell with several YOUHE access control systems and it works well with all the tested models. In this design, NE555 is set up to obtain 840Hz - 860Hz output with above 80% duty cycle. To get the more effective output we use small 3.5 inches, 8Ω tweeter with our prototype design. The PCB design and schematic of this design is available to download at google drive .

" Musical trees " is a part of creative art installation and this project is capable to produce different audio tones by detecting a human touch to its attached plants. The existing version of this driver is capable to monitor 8 plants and produce different sounds for each plant. A prototype version of "Magic Tree" project with 2 plant samples. This project is built around PIC16F628A 8-bit microcontroller and PT2399 echo processor IC. To drive the sensor electrodes we use pair of CD4011 quad 2-input NAND gate ICs. This prototype uses TDA7052 1W audio amplifier IC to drive the speaker(s). The existing firmware of PIC16F628A is designed to produce tones in between 155Hz to 1244Hz and this range can be changed by modifying the supplied firmware source code. In this design, the PT2399 echo processor IC is used to get the more natural (/ deep) sound effect by adding some reverberation to the output. Schematic and firmware of this project are available to ...

Few weeks back I got Victor SEA-50 stereo graphic equalizer from one of my friend. This is 10 band stereo graphic equalizer manufactured by Victor Company of Japan (now JVC Kenwood ) around 1970 - 1980. SEA-50 consist with 63 transistors and it provides ±12dB control range for 32 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 12 kHz / 16 kHz / 20 kHz center frequencies. The SEA-50 which we got is not working properly and most of its controls may generate distortion above +8dB and below -8dB. Apart from that left channel of this receiver has low volume and distortion. Defective transistors in control board (next to 2SA493). After few hours of checkup we identify few defective transistors ( 2SC982 ) in control board and we replace those with 2N3904 NPN transistors. Subsequent to this fix, all controls of SEA-50 start to work again on its full range (±12dB) by without producing any distortion or clipping.

Mullard 3-3 is quite popular 3W tube amplifier introduced by Mullard Ltd in 1956. A schematic and design detail of this amplifier is available in " Mullard Circuits for Audio Amplifiers " book and in National Valve Museum article . This amplifier is based on EF86 , EL84 vacuum tubes, and EZ80 full wave rectifier tube. In this project, we decided to construct this original Mullard 3-3 Amplifier with some slight changes and commonly available electronic components. Top view of Mullard 3-3 amplifier with 6P14P and 6J8 tubes. In our prototype, we replace the EZ80 tube with 400V 5A bridge rectifier which is commonly available in many electronic spare parts shops. Also, we replace EL84 with 6P14P pentode and EF86 with a 6J8 pentode. Both of these valves can directly use with this circuit and those values are available for a lesser price than EL84, EF86 tubes.