Dilshan R Jayakody’s Web Log

This project is about a wireless musical call bell, which I designed to meet some of my friend's requirements. This circuit design uses only the 4000 series CMOS logical ICs, NE555 , UM66 , and TDA7233 audio amplifier IC. For the remote control, we use a 433MHz 4-channel remote control module . This circuit is designed to work continuously with a low-power external 5V power supply. Prototype version of wireless call bell. The PCB in this call bell is designed as a single-sided PCB. The dimension of the PCB is 82mm × 50mm.  All the components in this circuit are commonly available through-hole-type components. The whole assembly process of this musical call bell is shown in the video attached to this document. The RF remote control module we use in this project consists of a remote control decoder and encoding IC. In our version, the transmitter (key fob) has a PT2262 encoder, and the receiver has a PT2272 decoder IC. In the prototype build, the receiver and transmitter are confi...

These days good quality oscilloscope is not an expensive instrument and, we can see it in most workbenches. With the advancement of oscilloscopes, simple testing tools such as logic probes are not as popular these days. However, if the oscilloscope or logic analyzer was out of reach, the logic probe is a handy instrument to check digital circuits.  Also, in some cases, a logic probe is an easy option to check the functionality of low-speed logic circuits because it provides a real-time visual indication of the logic state without adjustments or calibrations. Prototype version of the logic probe. The logic probe design described in this post uses common and inexpensive ICs, including the popular NE555 timer and LM393 low voltage comparator IC. At the time of this writing, both ICs were prevalent in the market and cost less than LKR50 (US$ 0.25). This circuit design using SMD components to minimize the board size. The dimensions of the soldered PCB are around 70mm × 14mm × 6.6mm, ...

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 .

Star test is the most recommended method to test and collimate telescopes . To do a " star test " we need to aim and track telescope with real star and most of the times this is quite difficult to do because of the fast movement of stars and bad sky conditions. Another problem with the real star is air turbulence and some times this effect may lead to false conclusions. However artificial star is an excellent alternative for " real star test " and in this post, we introduce easy to build "artificial star unit" to test and collimate telescopes. This unit is based on commonly available electronic components and it can operate with a 9V battery. At the time of writing this unit can build around LKR 1000.00 (Approximately 7.00 - 8.00 USD). In this given design, we use NE555 timer IC to generate PWM output to LED and this allows us to control the intensity of the artificial star. In our prototype we use high-bright 3mm white LED as our light source. Apa...

This is a very simple electronic doorbell circuit which is specifically designed to interface with commonly available access control systems. This circuit is designed around an NE555 timer IC and LM386 audio power amplifier IC. Because most of the access control systems use 12V power supplies this doorbell is also designed to work with 9V to 15V DC power source. Final view of our doorbell project prototype. We test this doorbell with several YOUHE access control systems and it works well with all the tested models. In this design, NE555 is set up to obtain 840Hz - 860Hz output with above 80% duty cycle. To get the more effective output we use small 3.5 inches, 8Ω tweeter with our prototype design. The PCB design and schematic of this design is available to download at google drive .

This is simple telephone locator-light which is used to identify the ringing telephone at the night / low light conditions. This unit only activates at low light conditions and it automatically turns off lights after 12 - 15 sec. from the last ring. This telephone locator is mainly based on NE555 timer IC and it is designed to work with 6V 0.5A - 1A power source. This given schematic support a maximum of two 3W power LEDs. During the assembly, it is important to place both LEDs and LDR in two separate positions to avoid any interference to LDR from LEDs. Also, note that in some counties it is illegal to connect custom circuitry into phone lines, please check your local regulatory bodies is concerned. Schematic and PCB designs of this unit are available to download at google drive .

These days many verities of alarm systems are available in the market. Some of them get triggered through touch and some type where a wire needs to broken to get triggered.  Both of these types of alarms have some limitations and problems. Wire based alarms are easily avoidable, noticeable and need some regular maintenance. Touch type alarms often pickup RF waves and get activated (because of that it need some controlled environment to function properly). In this project we design and develop LASER based burglar alarm system. Instead of wire(s) this system use LASER light wave and it can effective for more than 50m. Core features of this alarm system are: High audio output power (Max. 3W PMPO) Master light override switch Inbuilt alarm test functionality Memorized power state Quick response time (aprox. 10ms ~ 30ms) Support for wide input voltage range (15V – 25V DC) Easy to build and calibrate Compact size (aprox. 130 × 200 × 60mm) This alarm system is specifically ...

Electric Fences are designed to create an electrical circuit when touched by person (or animal). The circuits proposed in this article release 10kV electrical pulses to the fence-line and monitor the line status. This entire system is design to drive using 25V (5A) single-rail DC power source (using 5A power supply unit or pair of 12.6V Lead-Acid batteries). Main controller of this system is Microchip PIC12F675 – 8bit microcontroller. All the line monitoring, pulse generation and alarm system controlling is performed by this microcontroller. Some of the most notable features of this system are built-in audible alarm system, contactless fence line monitoring system, Support for wide range of step-up transformers (up to maximum of 10kV) and compact 10cm × 10cm PCB design. This system use standard electronic components (through-hole components) and SMD components in this provided PCB layout. All the project documents, schematics, PCB designs and firmware source codes are available...

In this project we design 2 channel D.C motor controller with pulse width modulation (PWM) based speed and direction control. This module is mainly design to drive 14.4V to 18V electric D.C motors. This motor controller is design to work with 18V - 1.5A D.C power source and it can be directly interface with general microprocessor / microcontroller system (without using any voltage level shifters). While at the prototyping stages we successfully couple this module with several NIDEC D.C fans and blowers which include D1751M24B7AP, E1331K12B7AZ-00, DME37KA, CF24DM506, etc. Control interface for this module is easy to use and at the designing stages we interface it with PIC16F887 and Atmega64 MCUs. Control interface of this module is consisting with 3 inputs (please refer the J3 in the circuit diagram) and using these inputs user may be able to select the motor, apply the brakes and also change the rotational directions of the motor(s). When constructing the circuit it is recommend...

In this design we present an electronic number display panel using low cost and low power electronic components. This proposed design is mainly based on CD4510 - CMOS up/down counter and SN74LS47 - BCD-to-Seven-Segment Decoder/Driver. With the existing configuration, this counter may be able to count (up/down) from 00 to 99 and it can easily extend to more digits by setting up additional CD4510 and SN74LS47 chip pairs. Current system is also equipped with the beeper (which based around NE555 timer IC) to indicate the increment or decrement of the count. This system is design to work with DC 9V – 12V (500mA) power supply and at the time of testing we use 10V (2.5A) DC power source to check this system. This proposed system contain 7805 regulator and it is necessary to apply suitable heat-sink to this regulator. In this project, we design PCB using double sided PCB and make dimensions and shapes according to the existing enclosure of old electronic number panel system. It is not ...