Dilshan R Jayakody’s Web Log

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.

This is a simple electronic project which we implemented for some local event to guide audience automatically with some prerecorded voice messages. The core component of this unit is ISD1820PY voice record/playback chip which is manufactured by Nuvoton Technologies . Except for ISD1820PY, this unit use commonly available low power LASER and LDR assembly to detect people. To drive the loudspeaker we use popular LM386 audio power amplifier. Thanks to ISD1820PY and LM386 this system can be implemented on a breadboard or on stripboard with a minimum number of external components. This circuit is designed to drive using 6V or 9V DC battery but it can also drive with 6V or 9V DC regulated power supply. To get 3.3V we use an LD1117V33 voltage regulator, but this can also be replaced with some commonly available 3.3V regulators such as LD33V, MC33269-3.3, etc. For the speaker, we use 4-inch 8Ω full-range speaker. A prototype version of electronic voice messenger. This unit can be u...

74181 is 4-bit arithmetic and logic unit introduced by Texas Instruments in March 1970 and it is known for being the first ALU in a single package. This chip is no longer in manufacturing but still, it is quite popular in CA ( computer architecture ) courses in many colleges. To test the behavior of this 4-bit ALU we decided to construct it on Altera MAX II CPLD. For this project, we choose EPM240T100C5 CPLD and logic design is implemented using Altera Quartus II . For logic design, we refer to Fairchild Semiconductor’s DM74LS181 datasheet. This setup is tested on basic EPM240 series development board with some mechanical switches and couple of LEDs. 74181 4-bit ALU test setup with the EPM240T100C5 development board. There are several test circuits available for 74181 ALU and our test setup is partially based on Electronics for Your (EFY) 1997 article. In another test setup, we use HEF4040 to drive, A and B operands of this ALU. The test setup attached to this article is t...