Saturday, November 15, 2014

Homebrew 5 element Yagi antenna for 144MHz

This is 5 element Yagi-Uda antenna for 144MHz amateur radio transmissions and receiving. This antenna is design using commonly available TV antenna parts. The CAD drawing of this antenna is available to download in my QSL.net pages and all the measurements in that diagram are in mm (millimeters). The total boom length of this antenna is around 1500mm and maximum span is 1016.10mm.

3D visualization of 5 element Yagi antenna

After the construction I test this antenna on 145.625MHz and got SWR of 1:1.3 with quiet lengthy, standard 50Ω RG-58 cable. With high quality shorter cable I archive SWR of 1:1.1 - 1:1.2.

Thursday, November 6, 2014

Simple CMOS FSK modem

This project is about 4046 PLL base simple FSK modem. Under given configuration this modem send digital signals over two frequencies and which is switching around 378kHz and 226kHz. In this system, modulator uses VCO of 4046, and demodulator is based on close loop mode of 4046 phase comparator and external LPF assembly.

This FSK modem is specifically design to transfer digital signals over mixed signal lines and it can directly use with any slow digital interfaces like UARTs. This system operates reliably under 10kHz range and we test it with standard TTL inputs.

1kHz Input signal and demodulated signal

1kHz Input signal and modulated signal

The given PCB of this system is based on SMD components but it can also construct using standard through-hole components.

During our prototyping we test this system with ATmega series microcontrollers and TTL signals sources. Because of 4046 CMOS implementation this unit can operate in between 3V to 12V by without using any external regulator(s) or level shifters.

Schismatic diagram and PCB design patterns of this project are available to download at elect.wikispaces.com.

Wednesday, October 22, 2014

Optically controlled servo motor

This is demonstration project to control servo motor movement using physical marker and normal video camera. In this project video camera capture the movements of marker and calculate rotation angle based on that. This calculated rotation angle is feed to the servo through small MCU based interfacing unit.

In this project video processing and tracking is performed using ARToolkit and controlling of servo is carried out using PIC16F628A microcontroller. RS232 interface is use to communicate between PC and microcontroller.

Interfaces in optical servo controlling system

This application detects movement of marker on Z axis (yaw) and transforms it into another numerical scale to manipulate the servo motor. Processing application is written using Visual C++ and configured to work on Windows operating system(s). The marker used for this application is needed to be a "square with some symbol" and user can train this system for any compatible marker. As per our tests, standard 3MP or higher grade web cam is sufficient for this system.

prototype assembly of servo driver and servo unit

To demonstrate the exact behavior video is much more suitable but my web cam is used for this project and I don’t have spare web cam to capture the operation of this project. As per our observations servo movement is highly sensitive to the changes of marker object and the movement of the servo motor is also linear and smooth. The propagation time is little bit slow due to serial interface and this can be improved by using high speed I/O interface like USB port.

The source code, servo driver schematic and firmware of this project are available to download at elect.wikispaces.com under the terms of the GNU General Public License version 3.0.

Saturday, October 11, 2014

Digitally controlled 2.1 channel analog audio power amplifier

This article introduces high quality digitally controlled 2.1 channel analog audio power amplifier system. This project is mainly based on TDA7377 AF power amplifier and PIC18F452 8bit microcontroller. Basic features of this receiver are 2 × 6W + 20W audio output power, ±14dB bass and treble controls, fully configurable +35dB bass booster for sub-woofer and satellite speakers and loudness switch.

This system use commonly available electronic components and all the integrated circuits are in DIL packages. This amplifier consists with few UI elements such as 2 push buttons and 1 rotary encoder. All the menu navigation can perform through rotary encoder.

Prototype version of 2.1 channel audio power amplifier project

Entire amplifier can build on 147mm × 80mm PCB and all the PCB design files are available to download at project homepage.

This is an open hardware project and all the firmware source codes, design files are covered with Mozilla Public License version 2.0. All the above content and complete documentation is available to download at http://elect.wikispaces.com.