Dilshan R Jayakody’s Web Log

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.