Dilshan R Jayakody’s Web Log

Logic probe is an essential item for digital electronic fault findings and constructions. In this project we design compact and simple logic probe with digital pulse generator. This circuit is based on 4069 logic inverter and 7805 voltage regulator. In this design we use 4069 invert module to drive the LED of logic probe and to build the oscillator circuit. We use TO-92 style of 7805 regulator to drive the 4069 chip and entire circuit can be build around 2.5cm x 12cm PCB (if you need to reduce the size in to more, use the SMD version of 4069 and 7805) All the resistors are 1/8w and SMD versions are also acceptable. To change the period of pulser modify C1 or/and R2. Complete schematic of digital logic probe with pulser is available to download in here .

In this project we developed 1.5A, 3V to 27V adjustable power supply unit based on LM723 voltage regulator IC. In this project we add some additional options to standard LM723 PSU circuit (available from National Semiconductors) to improve the safety and performance. When assembling the circuit it is necessary to attach suitable heat sinks to both 2N3055 transistors. Single heat sink for both 2N3055 are also acceptable. According to the initial design R8 must be 0.39ohms (5W), but most of the people say it is bit difficult to get 0.39ohms locally (Sri Lanka) so I change value of R8 to 0.47ohms (5W) and it is available in local market. During the testings and usage this system produce an excellent results for us. Complete circuit diagram of the power supply unit is available to download in here .

This is simple PIC microcontroller base project to generate Morse codes using standard PS/2 keyboard. This project based on Microchip’s PIC16F73 microcontroller and National semiconductor’s LM386 audio power amplifier. Software for PIC microcontroller is written using MikroC and all the source codes, schematic diagrams and other documents are available to download at here . In this project we choose PIC16F73 because of it’s 4KW (KWords) program memory, it is possible to replace this MCU with any suitable MCU which having 4KW (or more) flash memory. (For example Atmel AT89C4051-24SJ with different source code, Microchip PIC16F648 with some minor changes in source code, etc) Audio power amplifier of this project is based on National Semiconductor’s LM386. We choose LM386 because of its lower power consumption and compactness. User may also replace this module with suitable power amplifier (for example Philips TDA7052, TDA8551, National’s LM4906, etc.) PIC16F73 software is develop...

In this project we developed user programmable automatic night light using Microchip's 8bit MCU – PIC12F675. In this design user may be able to program and store the time duration of the master light. Compared with other designs this circuit use transformerless power supply, and TRIAC to control the master light. Complete MCU software source code, operating guides and circuit diagram of this project is available to download at here . To get more information about transformerless power supply please refer the Microchip application note AN954 , and ST application note AN438 for MCU and TRIAC interfacing.

3.3V is now widely used in electronic circuit projects (especially in digital electronics). These days several MCUs, CPUs and Digital interfaces (e.g: USB, Ethernet) uses 3.3V and in this project we developed suitable compact power supply unit for these projects. This project is mainly based on National Semiconductors LM1086-(3.3) power regulator. With the suitable transformer this circuit may capable to deliver 3.3V (during the testing stages we get 3.29V) with 1.5A of maximum current. If you need more current please use LM1085 (3A) or LM1084 (5A) instead of LM1086 (U1). All the circuit diagrams and PCB patters for this project are located in here . To get the maximum performance, replace C2 and C3 with 10MFD/25V tantalum capacitors. Please note that it is necessary to install good heatsink to the LM1086-3.3 (U1) regulator.

In this project we develop automated telephone remote control system to demonstrate the functionality of MT8870 DTMF decoder. This project mainly based on MT8870 DTMF decoder and ATtiny2313 MCU. When this system connects to the phone line it monitor the status of the phone line and take the control of phone line when it detects the ringer, after that user may be able to control specified I/O port using appropriate keys. Finally user can issue predefine key combination to shutdown the phone line. Schematic diagram, source codes for ATMEL ATtiny2313 are available in here and all the source codes are developed using WinAVR (with Atmel AVR Studio 4). Please note that this project is developed for demonstration purposes only, some of the system states may not handled with the given source code.

These days we are working with VIA Technologies PC-1 series mainboards and compared with standard main boards these boards have special features and advantages. Main advantage is, its lower price and low power consumption . Like most modern motherboards these boards also have built-in Sound cards, Network adapters, SATA Support and build-in Video interface. VIA PC-1 series is specially design for low power computing and users may be able to run this mainboard with 150W power supply. There are several PC-1 mainboards are available and we are mainly worked with following units, PC-1000 Mainboard Powered by VIA C3 – 800MHz microprocessor 100/133 MHz FSB DDR-I Memory up to 1GB. VGA up to 64MB 4 USB 2.0 ports 10/100 LAN interface 1 PCI Slot Realtek AC97 audio codec Mini ATX form factor (170mm x 170mm) Price : Rs. 5000.00 (Sri Lanka Rupees) PC-3500 Mainboard Powered by VIA C7-D – 1800MHz microprocessor 400/800 MHz FSB DDR-II Memory up to 2GB VGA up to 256MB 6 USB 2.0 ports 10/100 LAN inte...