Monday, May 21, 2018

Banana Pi DLNA media server

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 stages, we notice that both hard disk drive and BPI A20 CPU get heat-up during the long runs and to cool those components we decided to build simple fan controller with temperature monitor. After couple of designs we finally build BPI support board with above 5V regulator and LM311 based fan controller. To make it simple we construct above two components in 80mm × 53mm single side PCB. Both schematic and PCB design of this unit is available to download at Google drive.

5V regulator and fan controller board.
When constructing above switching regulator pay special attention to 100µH inductor (L1) and associated components in switch regulator stage. Specially if inductor is not up to the specification SATA interface may get fail with I/O errors. We got this problem while we testing this regulator in breadboard.

To monitor system temperature, we use LM35 temperature sensor with LM311 comparator. Fan trigger level can adjust using RV1 trimpot.

To drive this regulator and fan controller board, we use commonly available 12V 10A SMPS unit. Because we plan to run this server for 24×7 we choose quite reliable SMPS for this system.

Monday, May 7, 2018

AF signal injector and tracer

Signal injector and tracer is very useful device when troubleshooting electronic audio equipment. We decided to build this signal injector by inspiring the article available at 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 local market. After few months wait we got couple of ICs from eBay for LKR 600.00. The second issue is it’s 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 LM358 operational amplifier IC which is commonly available in local market (for LKR 15 to 20). For the power amplifier we use LM386 low voltage power amplifier IC (which also costs around LKR 10 - 15). Our design is almost similar to EPE design and the only major addition is LM386 AF power amplifier stage.

3D view of signal injector & tracer PCB.

We build this signal injector and tracer on a single side PCB. Compare with original EPE design this unit consumes more power and it is not designed to drive using a battery. The AM RF demodulator probe (Page 30 - 31 on same magazine) also works well with this unit.

In supplied PCB we does not include attenuator circuit and in our prototype we build it using point-to-point wiring method (on top of the selector switch).

Our signal injector and tracer schematics and PCB designs are available to download at google drive. For more detailed overview please check the June 2016  issue of Everyday Practical Electronics magazine. 

Tuesday, April 17, 2018

6 channel speaker selector

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 E2PROM 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 use Omron G2R-2-24V relays and got excellent results. Listener can change channel by pressing the (J2) push button. To disconnect / mute the channel, hold down J2 push switch for 5 - 10 sec.

Due to simplicity of the design, we construct our prototype version of this speaker-selector in Perfboard. When constructing this circuit make sure to attach suitable separate heatsinks to LM317 and L7805 regulators. Also to get higher stability we highly recommend to place C7 (0.1MFD) capacitor in between Pin 5 and 14 of U1 (PIC16F88) MCU. For seven-segment display we use 20mm single digit common cathode red color SSD.

Speaker / amplifier connection terminals.

This speaker selector is an open hardware project, all it’s source codes and schematics are available to download at google drive and All it’s content are released under the terms of MIT and CC BY-SA licenses.

Saturday, March 17, 2018

Electrical wiring of the house

In last year we spend 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 large number of electrical points we decided to use 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 below diagram.

High level electrical wiring diagram up to distribution boards

In 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 the 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) circuit is bit complex due to the change-over-switch. We use  change-over-switch to connect additional power source into AC line during the power failures. For the change-over-switch we use DIN-rail type, 2-way 2-pole 40A change over switch. In here also we use two indicator lights to show both mains and external (generator) line status.

4-pole isolator and RCCB mount