Dilshan R Jayakody’s Web Log

Couple of months back we decided to create our own media server to store our MP3s and digital photographs. But it gets postpone several months due to unavailability of main-boards and other resources. Finally, after reviewing several prototypes we decided to build our media server using Banana Pi (BPI) and MiniDLNA . Before finalize BPI we checked several main-boards which including Raspberry Pi B+ , Orange Pi One and BeagleBone Black . Out of all above main-boards we choose BPI M1 because of its inbuilt SATA2.0 interface, Gigabit Ethernet port and availability in local market. Final view of DLNA media server setup. As an operating system we use Bananian Linux , which is Debian derivative for BPI platform. To sore all our content, we use Seagate 1TB SATA 3.5 inch hard disk drive. Bananian OS and other packages are loaded into 8GB SD card. To power both BPI and SATA disk drive we design PSU using LM2576-5.0 step-down switching regulator IC. Also during the prototyping sta...

Signal injector and the tracer is a very useful device when troubleshooting electronic audio equipment. We decided to build this signal injector by inspiring the article available in June 2016 - Everyday Practical Electronics (EPE) Magazine ( Audio Signal Injector and Tracer by John Clarke - Page 22 to 29). The signal injector design in EPE magazine is simple but we got few issues while constructing that circuit. The main issue is that LMC6482 is not available to buy in the local market. After few months wait we got a couple of ICs from eBay for LKR 600.00. The second issue is its output is not enough to drive most of the loudspeakers. After prototyping EPE design we decided to build similar sort of signal injector and tracer with commonly available ICs and with more powerful power amplifier stage. For our design, we use the LM358 operational amplifier IC which is commonly available in the local market (for LKR 15 to 20). For the power amplifier, we use LM386 low voltage power...

If you are an audio enthusiast and if you have multiple audio systems and speakers, you may definitely need to have a speaker selector switch. These switches allow you to route a audio signal through a switching system and distribute it to various speakers. Using this listener can select single amplifier – speaker combination through the switch. We mainly design this switch to share our speaker system with multiple audio amplifiers. We design this switch to handle 6 stereo audio channels. Final view of 6 channel speaker selector prototype. This switch is based on PIC16F88 - 8bit MCU, ULN2803 Darlington transistor arrays and 12 DPCO relays. MCU is the core component of this switch and it control all relays, seven-segment display and store last channel in E 2 PROM memory and restore it during next power-up. In this system all audio lines are switching using 12 DPCO relays. To get optimal results we recommended to use good quality relays with thus switch. In our prototype we u...

In last year we spend a lot of time and effort to wire our new house by ourselves. To complete this job we took nearly 2 ½ months and it includes wiring, fixing electrical fittings, communication equipment, etc. In this post, we describe how we archive this task with some technical details. Due to a large number of electrical points, we decided to use 3 phase electrical wiring in our house. To make it simpler we divide entire house wiring into 3 isolated circuits with 3 separate distribution boards. High-level design of our AC wiring systems is illustrated in the below diagram. High-level electrical wiring diagram up to distribution boards In the above circuit, the 3 phase AC line is first fed into 4-pole 40A isolator . Then it connected to 4-pole RCCB with 3 separate indicator lights. We use indicator lights to see the status of each phase, easily at any time. After RCCB we fed each phase into 3 separate distribution boards. As seen in the diagram the first (phase) circui...

In this post, we describe the fan controller which we designed for our 9U wall mount server cabinet. This fan controller is designed to drive a 12V DC cooler fan with pre-configured intervals or by monitoring the temperature of the server cabinet. The final version of the fan controller with DC brushless fan and 12V - 60W PSU. Core components of this fan controller are CD4060 binary counter, LM35 temperature sensor, and LM358 operational amplifier. In this design, CD4060 has used as long duration timer and it can be configured to trigger cooler fan from 1-minute and up to 4-hour. In this design, an LM35 temperature sensor is used to activate cooler fan in specified temperature. This sensor stage is useful to drive cooler fan when timer stage is in an inactive state. To control the cooler fan we use AP9971 dual N-channel power MOSFET transistor. We design this system to drive 12V cooler fans up to 2A of current. To test this controller we use commonly available 120mm × 120mm...

This is an automatic Cat6 / Cat5 network cable tester designed using NE555 timer and 4017, decade counters. This unit test all 8 wire lines of twisted pair network cable and indicate pass/fail status with a single LED. We design this unit to test network connectivity issues in Cat6 / Cat5 cable systems and it is capable to check both crossover and straight-through type network cables. A prototype version of network cable tester. The recommended way to construct this circuit is on PCB. Both Master and Salve units need to be built on two separate boards. To perform test one end of the network cable must be connected to the Master unit and other ends need to be connected to the Slave unit. After connecting both Master and Slave units press " START-TEST " (S1) button to perform the test. Status of the cable is indicated through LED2 ( PASS indicator). PCB and schematic of this unit are available to download at google drive and easyeda.com .

Sony STR-AV780 is a combined receiver and audio/video control center. This receiver is manufactured by Sony in around 1986 and it is capable to deliver 2 × 80W audio output power with 8Ω speaker load. The STR-AV780 which I got had two problems. The first problem is in the power amplifier stage and it produces distortion in high frequencies. The second problem is in FM radio receiver and it is completely dead. The power amplifier of STR-AV780 is based on two Sanyo STK4042 XI AF power amplifier ICs. To fix the distortion issue we replace all the electrolytic capacitors in both STK4042 power amplifier boards. After replacing capacitors distortion issue got fixed and the power amplifier starts to produce a clear output waveform. The FM receiver of this AVR is mainly based on 2 ICs. For IF stage it uses LA1235, and to demodulate FM stereo signal it uses LA3401. Apart from that Sony CX7925 is used as PLL frequency synthesizer. The front end of FM tuner is based on a couple of transist...