Monday, July 9, 2018

Sensor framework for Data Logging

This is simple sensor kit to drive 8 active or passive sensors and log it's data into remote Android application. This system also have an option to activate external device(s) based on specified threshold of sensor data.

This sensor controller is mainly build around Raspberry Pi Model 3 B+ and PIC16F877A MCU. PIC16F877A MCU is used to interface/select sensors and it's built-in 10bit multi channel ADC is used to capture the analog signals from sensors.

During the prototype stage following sensors are tested with this system:

  • LM35 precision temperature sensor
  • MQ7 Carbon Monoxide gas sensor
  • Electret Microphone
  • NSL-19M51 LDR
  • HC-SR501 PIR sensor
  • A3144 Hall effect sensor

Apart from above list this system can use to drive and capture most of the other analog/digital sensor signals such as current sensors, pressure sensors, chemical sensors, humidity sensors, etc.

In this system Android monitoring application is designed to connect with the sensor platform through a network link (such as using Wi-Fi or mobile data network) and it can also control this sensor platform via this link.

This given version of Raspberry Pi server is designed to handle only one client and it can be easily extend to multipal client support by modifying the communication protocol of Node.js application and Android application. We build this system entirely for demo purposes and we didn't get a chance to extend it to multi-client support.

Android control and monitoring application.

The trigger system of this system is based on MOC3041 optocoupler and BT138 TRIAC. At prototyping stage we use this system to drive 5W - 230V incandescent light bulb. Because of high current rating of BT138, this system can use to drive AC equipment(s) up to 10Amps.

All the schematics and source codes of this project are available to clone at

Tuesday, June 12, 2018

ICOM IC-R71A receiver restoration

Recently I got ICOM IC-R71A receiver from one of my friend. ICOM IC-R71A is multi-mode quadruple superheterodyne receiver with frequency range from 100kHz to 30MHz. When it comes to my workshop it's completely dead but outer casing and front panels are in really good condition. Before   troubleshoot the receiver, I download both user manual and service manual from the internet. As like all ICOM products this receiver also comes with very detailed user manual and service manual.

Restored ICOM IC-R71A receiver

As I observed this receiver consist with many PCBs which including:

  • Main board
  • Front boards (altogether 7 boards, which including 1 main board known and matrix board and 6 small PCBs)
  • PLL board
  • RF board
  • Logic board and RAM board
  • Power supply board

In addition to above boards there are some previsions in this chassis to install other optional boards such as FM board.

After observing the power supply board, I notice couple of dry joints in rectifier module and 2SD880 transistor. After re soldering power supply unit starts to work and receiver got powered up.

After checking it for few minutes I noticed couple of problem with this receiver. The main issues which I noticed are faulty RF gain controller and very low audio output from the receiver.

While checking the boards I notice that most of the electrolytic capacitors in this unit are in quite bad state. I noticed most of the electrolytic capacitors in PLL board are in very bad condition and most of them are in "leaky" state.

After checking other PCB boards, I decided to recap all the electrolytic capacitors in this receiver. I bought all necessary capacitors from the local market and it costs me approximately LKR 300. For most of the values I choose Nichicon capacitors because they are commonly available in local market. For other values I use Panasonic and ELNA capacitors. Because 10V capacitors are quiet hard to find I use 16V capacitors instead. The complete list of capacitors are available in my QSL home page.

I took extra precaution while working with logic board because it consists with battery powered memory module. (According to ICOM, it's DRAM uses this lithium battery to retain its content. If it got erased, radio may become unusable.)

After replacing all the capacitors receiver starts to work perfectly and I got amazed by its performance. Compare with my existing receivers this receiver performs extremely well and its sensitivity is super impressive.

More details about the restoration is available at

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.