Dilshan R Jayakody’s Web Log

This is a simple electronic project which we implemented for some local event to guide audience automatically with some prerecorded voice messages. The core component of this unit is ISD1820PY voice record/playback chip which is manufactured by Nuvoton Technologies . Except for ISD1820PY, this unit use commonly available low power LASER and LDR assembly to detect people. To drive the loudspeaker we use popular LM386 audio power amplifier. Thanks to ISD1820PY and LM386 this system can be implemented on a breadboard or on stripboard with a minimum number of external components. This circuit is designed to drive using 6V or 9V DC battery but it can also drive with 6V or 9V DC regulated power supply. To get 3.3V we use an LD1117V33 voltage regulator, but this can also be replaced with some commonly available 3.3V regulators such as LD33V, MC33269-3.3, etc. For the speaker, we use 4-inch 8Ω full-range speaker. A prototype version of electronic voice messenger. This unit can be u...

74181 is 4-bit arithmetic and logic unit introduced by Texas Instruments in March 1970 and it is known for being the first ALU in a single package. This chip is no longer in manufacturing but still, it is quite popular in CA ( computer architecture ) courses in many colleges. To test the behavior of this 4-bit ALU we decided to construct it on Altera MAX II CPLD. For this project, we choose EPM240T100C5 CPLD and logic design is implemented using Altera Quartus II . For logic design, we refer to Fairchild Semiconductor’s DM74LS181 datasheet. This setup is tested on basic EPM240 series development board with some mechanical switches and couple of LEDs. 74181 4-bit ALU test setup with the EPM240T100C5 development board. There are several test circuits available for 74181 ALU and our test setup is partially based on Electronics for Your (EFY) 1997 article. In another test setup, we use HEF4040 to drive, A and B operands of this ALU. The test setup attached to this article is t...

AN6877 is linear AF level meter IC produced by Panasonic and it is commonly found on much audio equipment. This chip is no longer manufactured by Panasonic and finding replacement chip for AN6877 is also quite difficult. The circuit described in this article is designed to replace AN6877 base LED drivers and it is based on commonly available components. This replacement LED driver is designed using 10, MMBT3904/2N3904 transistors and it can easily modify to get the necessary number of outputs. During the prototyping stages, we test this driver with a minimum of 7 LEDs (AN6877 configuration) and up to 12 LEDs. This LED driver is designed to work with 9V to 12V DC power source. With 7 LEDs and 9V power source, this module can directly replace AN6877 base LED driver modules. Schematic and PCB design related to this LED driver is available at google drive .

ZFM-20 is an optical fingerprint sensor module series developed by Zhiantec . Resolution of these fingerprint modules are 256×288 pixels and depending on the module it can be accessible over UART or USB interfaces. Other than capturing fingerprints this module has inbuilt DSP to process and verify captured fingerprints. This ZFM-20 fingerprint library is developed to capture and retrieve fingerprint images from the above sensor module. The main purpose of this library is to use ZFM-20 sensor with PC as a low-cost fingerprint capture unit and because of that, in-module fingerprint processing and verification functions are not implemented in this library. ZFM-20 fingerprint sensor test setup with CH340G serial to USB converter. ZFM20-LIB is x86 native shared library and it's implemented using Lazarus / FPC . This library is developed to use with most of the programming languages which including C , C++ , Delphi , FPC , Microsoft .net framework based languages, etc. Objec...

This is a single chip dynamic microphone preamplifier which is design to drive using commonly available 12V single rail power supplies. Preamplifier in this article is built around popular NE5532 dual low noise operational amplifier IC and this preamplifier is specifically constructed to drive professional 600Ω dynamic microphones. Internal view of a dynamic microphone preamplifier prototype. This preamplifier consists of two amplifier stages and the initial amplifier is designed to get 36dB gain and final preamplifier is used to get 16dB of gain. Preamplifier gain controller is placed in between those two amplifiers and this separation allows reducing clipping in the output waveform. In prototyping stages, we test this preamplifier with few 600Ω dynamic microphones with a TDA2050 power amplifier . According to our observations, this unit produces excellent output with all of these microphones. To get professional results to use this preamplifier with 12V battery or with regu...

The phantom power supply is widely used in the audio industry to power the active microphones over single audio cable. Most of the phantom power supplies deliver 48V DC over the balanced audio link and power supply unit described in this article is also based on the same technique. The phantom power supply in this article is based on TL783 high voltage regulator IC and 230V - 50V step down transformer. Like most of the phantom power supplies, this power supply is also design to connect in between an active microphone and audio mixer devices. PCB of 48V Phantom power supply. Schematic of this power supply unit is self-explanatory and PCB design is also based on commonly available through-hole components. For the step-down transformer, we use commonly available 230V - 25V-0-25V 1.5A transformer. During the construction, we recommended using shorter wires between PCB and XLR sockets to reduce the noise. PCB and schematic of this power supply unit are available to download at...

Resistor box is a quite useful instrument in analog electronic based design and prototyping tasks. It can easily build with few sets of resistors and with a couple of rotary switches. This quick post is about resistor box which we construct recently using 5W wire-wound power resistors. For this resistor box, we use five, single pole 12 position rotary switches and 50 wire-wound resistors. It gives 5 dials to controls 10Ω, 100Ω, 1KΩ, 10KΩ and 100KΩ steps. Final view of homebrew resistor box. Internal view and high-resolution photographs of this resistor box are available at my Flickr page . Schematic of the resistor box is available here .

TEA5767 is electronically tuned FM stereo radio receiver comes from NXP for low voltage applications. TEA5767 based radio modules are now common in the field and this project is based on Samsung TT-502 radio module . The main objective of this project is to design low-cost FM tuner based on this TT-502 / TEA5767 module and commonly available electronic components. In this receiver the main controller is ATmega8 MCU, except to that TDA2822 is used as AF power amplifier, PT2257 is used to control the volume. In this given design MCU, PT2257 and TEA5767 radio module are set to work with a 3.3V power source. The LD33V voltage regulator is used to obtain 3.3V from the supply voltage. To control the receiver, MCU provides five push buttons. Those can be used to control volume, perform an automatic scan and manual tuning. The final version of TEA5767 based FM radio receiver. The firmware of this receiver is developed using MikroC for AVR and it is available to download with proje...

Audio output transformers are heavily used in a vacuum tube and some (older) transistor base audio power amplifiers, but these days output transformer are quite hard to find and expensive item. For homebrew projects, the best option is to construct those transformers by ourselves and this script helps to calculate winding parameters for those transformers. This " AF output transformer calculator " script is written using Python and it works with most of the commonly available Python interpreters . The script is available to download at google drive under the terms of GNU General Public License version 3.0 . Homebrewed 25k: 4 output transformer Once supplied the input parameters this script provides a winding ratio, the number of turns required for primary and secondary winding and required copper wire gauges for both primary and secondary windings, etc. We construct several AF output transformers based on results of this script, which including transformers for M...

This post is about experimental USB to 3.3V/5V serial TTL adapter which we build recently to work with both 5V and 3.3V MCUs. This project is mainly based on CH340G seral-USB chip. CH340G is cheap and commonly available serial-USB convert IC and now it's commonly found on Chinese versions of Arduino development boards. FTDI's FT232 is another possible alternative for this kind of project, but we drop it because of its famous device driver base chip locking issues . Also, compare with FT232, CH340G is cheap, commonly available and simple to construct with a minimum number of components. In this module, we incorporate a 5V/3.3V voltage selector switch to avoid interface matching issues due to different voltage levels of mainboard/MCU and serial TTL adapter. A prototype version of CH340 USB to serial adapter. In prototyping stages, we use CH340G with breadboard by using SO-16 to DIP16 adapter and supplied PCB is also based on using the same adapter. Except for CH340G ...

HAKKO 907 is popular and commonly available soldering iron in the electronics field. To drive those soldering irons user needs to have HAKKO or any other compatible soldering station. The biggest problems with those soldering stations are there higher price tags and limited availability in the local market. Because of those problems, we decided to create our own soldering station, and for that, we choose " Chinese " version of HAKKO 907 soldering handle. Now Chinese versions of 907 compatible irons are available on eBay for less than 5USD. As per our observations, those Chinese versions of soldering irons look and perform almost similar to genuine HAKKO 907 iron(s). To keep it simple we choose LM358 dual operational amplifier IC to monitor the 907's thermocouple and drive the TRIAC. The entire control circuit of this soldering station is powered by single rail 5V DC power supply. To drive both handle and station we use 12V-0-12V 8A step-down transformer. Interna...

This is contactless DTMF ( Dual Tone - Multi Frequency ) switch to control 16 channel relay boards. This module can turn ON/OFF relays based on DTMF singles which captured from its microphones. This project is building using 4 commonly available ICs which including TL084, TL081, CM8870, and 74LS154. TL084 is used as microphone preamplifier and LPF. TL081 act as combiner and CM8870 is used to decode the DTMF inputs. 74LS154, the demultiplexer is used as line selector. In this circuit TL084 and TL081 and replace with any compatible operational amplifier IC. During our prototyping, we replace TL084 with LM324, TL074, and TL081 with TL071 and got identical results. For the microphones, it is highly recommended to use omnidirectional condenser microphones. In our tests, we get good results when both the microphones are in the 90⁰ plane. This circuit is design to work with single rail 5V DC power source and its output terminal ( SV1 ) is compatible with most of the 16 channel relay bo...

UC3844 is a popular current mode controller which is commonly found on DC-to-DC converter circuits and switch mode power supplies. This motor speed controller is also based on UC3844 and it is specifically designed to drive 20V - 24V DC motors. In this given configuration UC3844 produces (approx.) 50kHz to 240kHz PWM output and this range can be adjusted by changing the value of C2 timing capacitor. As per the datasheet, UC3844 is capable to produce PWM output frequency up to 1MHz. This circuit is quite sensitive to the noises, and to get the accurate output to construct this circuit on PCB. As per our observations, long wires on the oscillator circuit may change the stability of the output signal. According to the ON semiconductors , UC3844 has now discontinued product but it is still commonly available in the market for less than Rs. 40.00 (LKR). For this circuit either DIP (UC3844N) or SMD (UC3844D1) version of UC3844 can be used but the PCB design available with this arti...

This is a quick post about EAGLE parts list generation script which I was written to replace existing " part2html.ulp ". This script generates a more organized and detailed BOM HTML file and it can directly replace " part2html.ulp ". This script is tested with EAGLE 6.6.0, but it can also work with older versions of EAGLE software. This script is available to download at http://github.com/dilshan/bom-gen with usage details.

FlashProg is USB base flash memory programmer to work with 3.3V serial flash memory devices. This programmer is specifically design to read, program and configure 25x series, serial flash memory devices which are commonly used to store BIOS in PC mainboards. Originally we design this project to read and program BIOS of Foxconn G31MXP mainboard. Our version of G31MXP contains Macronix MX25L8005 8M-Bit serial flash memory and we use this programmer to load some of our custom BIOS to this serial memory. MX25L8005 SPI flash memory on Foxconn G31MXP mainboard FlashProg programmer is built around Atmel ATmega8A microcontroller with standard through-hole type components and it support for both 32 bit and 64 bit Windows and Linux operating systems. All the compiled binaries for both the platforms are available at project home page at flashprog.sourceforge.net . This programmer use very few components and it can be easily constructed on breadboard or on PCB. Both EAGLE and PDF...

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist...

This is 5V 3A power supply to drive two USB based devices simultaneously. This power supply is design around LM2576-5.0 switching regulator IC and the main reasons to choose this IC is its low parts count, small heat sink requirements and its inbuilt current limit protection feature. Prototype version of 3A USB power supply We specially design this power supply to work with development boards / single board computer (SBC) platforms such as Raspberry Pi , Banana Pi , BeagleBone , etc. This power supply can also be used to provide power to USB OTG peripherals over USB Y cables. We test this setup and got successful results with Huawei Ascend P6 mobile phone.

DC millivolt sources are often used for thermocouple simulations, DMM, ADC, and analog circuit calibrations and fault findings, etc. Most of the DC millivolt circuits are based on expensive (and sometimes hard to find) operation amplifier like OP7, LT1077, etc. In this article we introduce low cost DC millivolt source based on commonly available LM308 precision operational amplifier, ICL8069 low voltage reference and 78L05 voltage regulator ICs. This millivolt source is design to obtain 200mV - 700mV DC output with 100Ω impedance. At the time of writing we spend Rs.800.00 ( LKR ) to complete this project. Finished view of DC millivolt source. The most expensive component in this project is Bourns 10K linear multi-turn potentiometer. We use Bourns potentiometer because of its reliability and durability, but any 10K linear multi-turn potentiometers can be used with this circuit. The output impedance of this millivolt source is set to 100Ω to work with most of the high impedan...

This is 4-way stereo unbalanced distribution amplifier (DA), which can be used to distribute (or split) input audio signal to 4 isolated audio devices. Distribution amplifier in this article is based on commonly available TL072 and TL074 low noise operational amplifier ICs and 7812/7912 voltage regulator ICs. To drive this system, 12V-0-12V or 15V-0-15V 1000mA center tapped step-down transformer is required. Also note that the operational amplifiers used this circuit can be replaced with identical high-quality versions like OPA4134, OPA2134, etc. In our prototype, we use the TL07x series because of its availability and lower price. PCB design of stereo DA project To avoid any interference it is highly advisable to construct this circuit on PCB and also use double core screened wires for all external audio connections. Schematic, PCB and "EAGLE project files" of this project are available to download at google drive .

When it comes to AVR microcontrollers the most common programming option is In-System Programming ( ISP ). ISP interface is easy to use but in some scenarios it is totally unusable. The most common scenario is with some wrong fuse bit values. For example if we program SPIEN or RSTDISBL fuse bits, AVR microcontrollers may not respond to any in-system programmer(s). To overcome these problems the next available option is high voltage programming mode. In High voltage programming mode, 12V programming voltage is applied to RESET pin of target AVR microcontroller and user can change configuration fuses of AVR MCU with minimum amount of risk. The only drawback in this mode is that target microcontroller must need to be removed from the board to reprogram. Most of the AVR high voltage programmers are expensive and difficult to find in ordinary electronic shops. As a solution we implement USB base high voltage parallel programmer for AVR microcontrollers and it allows programming, readi...

This post is about beat frequency oscillator (BFO) module which is used to receive SSB and CW signals from the ordinary shortwave receiver. The original circuit which is related to this post is obtained through the internet and we modify it to get more precise output with commonly available electronic components. ( Unfortunately at the time of writing this original link is no longer accessible due to a dead link. ) This module consists of two general purpose NPN transistors and we select 2SC828 because of its availability in the local marketplace. For the crystal, we use commonly available 455 kHz ceramic resonator. Assembled 455 kHz BFO module. This BFO unit is easy to construct and may not need any test instrument for calibration. To receive the SSB signals, power this unit with regulated 5V or 6V DC power source and place BFO module near to the shortwave radio receiver. To get good results to place output wire of BFO near to the IF amplifier section of the target receiver....

This is two transistors and two IF transformer based superheterodyne receiver which is designed to receive 13m to 41m bands. With quite good external antenna this receiver performs similarly to the commercially available shortwave receiver and its audio quality is at a very satisfactory level. Prototype version of two transistor superheterodyne shortwave receiver. This receiver can be constructing on PCB, breadboard or commonly available veroboard or stripboard. For tuning use Polyvaricon or air variable capacitor. For precision tuning, connect small trimmer capacitor with parallel to variable capacitor’s gangs or use mechanical wheel assembly with the variable capacitor. This receiver is designed to work with 9V regulated power supply and it requires an external AF amplifier to drive the headphone or speaker. In our testing, we use a TDA2050 audio power amplifier with this receiver. With small wire antenna, this receiver is capable to receive most of the stations which in...

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 .

SL414 is combined audio preamplifier and power amplifier IC manufactured by National semiconductors in early days. This amplifier is designed to operate in 10V to a 20V range and deliver 3W (R.M.S) audio output power into the 7.5Ω load. The frequency bandwidth of this IC is between 30Hz to 18kHz and with the 8Ω load, it produces 0.5% T.H.D on 3W. The most uncommon feature of this IC is its EP-10 package. This EP-10 package is common to most of the SL4xx series amplifiers and thanks to its inbuilt screw it is really easy to attach heat-sinks to these ICs. EP-10 package of SL414 audio amplifier IC. During our prototyping, we try several SL414 amplifiers and most of them give quite satisfactory results to us. Link to most stable SL414 design is available at the bottom of this article. As per our experiments, to archive best results it is mandatory to build this amplifier on PCB with screened wires. Also to get the good results to make sure to drive this amplifier with a regulat...

This is PIC16F73 base digital data capture unit with optional EMF reader. This data capture utility is design to work with most of the analog sensor inputs and by default, it is equipped with the EMF reader module. This unit use PIC16F73's internal 8bit ADC to capture the analog signals. EMF reader unit in this schematic is useful to detect variations of EM field in the environment and it is mainly built around uA741 operational amplifier and 12mH detector coil . Normally EMF meters are used to trace electric wires, find hidden transmitters, and diagnose electric wiring problems ( and to find ghosts too ☻ ). This digital data capture unit can operate in 2 modes. In the first mode, it directly converts an analog signal into digital data and transferred to the host via a serial interface. In second mode it displays captured signal in 5 LED bar graph either slow or high-speed capture modes. This unit is designed to work with 5V 500mA power source and to get optional EMF reading...

BA1404 is quiet famous FM stereo transmitter IC manufactured by ROHM Semiconductor . This 18pin chip contains FM stereo multiplexer, 19 kHz pilot tone generator and RF output stage with the oscillator. The FM transmitter in this article is also based on BA1404 and 78L33 voltage regulator. The FM transmitter in this article is specifically designed to transmit audio signals generated by PC/Laptop sound cards. To archive this goal, this transmitter is designed to drive using a 5V DC power source. Except for Q1 (38 kHz crystal) and L2 (oscillator inductor), this transmitter uses commonly available electronic components. 38 kHz crystal is vital to generate 19 kHz pilot tone and this crystal is available to purchase in several web stores. For L2, wind 3 turns of 22 S.W.G enameled copper wire on 5mm bobbin with an adjustable ferrite core .  This variable inductor is used to select the output frequency of the transmitter. To archive good quality output and frequency stability ...

This is a quick post about 100W RF dummy load which we build to use with HF and VHF transmitters and transceivers. This dummy load uses two non-inductive 100Ω 50W thick film power resistors manufactured by Vishay Sfernice and both these resisters are connected in parallel to achieve 50Ω impedance. The final version of 100W RF dummy load. Outer-casing (which also act as a heatsink) of dummy load is constructed using four bonded fin 50mm × 115mm × 20mm heatsinks. During our testing, we got flat 1:1.2 SWR with this dummy load. Internal view of 100W RF dummy load. Above mentioned 100Ω 50W power resistors are obtained through Farnell element14 .

Steganography is a method of hiding information and one of the techniques is to hide an image inside a "cover image" by without distorting the supplied "cover image". ImageHide is command-line driven console application to perform this task and it is capable to hide/embed a colored or gray-scale image inside another color or gray-scale cover image and/or extract an embedded image from the supplied "cover image". This application is developed using FPC / Lazarus and it can execute on any FPC supported operating system which including Linux, Windows, Mac OS, etc. ImageHide is an open source project and its source code is available at https://github.com/dilshan/image-hide under the terms of GNU General Public License version 3.0 . Compiled binaries of ImageHide are also available for both Linux and Windows operating systems. As an input, this application accepts bitmap, PNG or JPEG image formats and it can export the processed image as bitmap or PNG ...

Audio Signal Generator (or AF Signal Generator) is often used in RF and AF base designing and experiments. In this article we introduce less complex AF signal generator based on commonly available electronic components. The heart of this AF signal generator is Intersil ICL8038 precision waveform generator/voltage controlled oscillator IC. ICL8038 is a function generator capable of producing sine, square and sawtooth waveforms at same time. In this project we combine ICL8038 with inverting and non-inverting amplifiers to get above mentioned 3 waveforms with 0° and 180° phase differences at the same time. Those inverting and non-inverting outputs help to use this AF signal generator with balanced audio systems. Final version of AF signal generator. The given schematic and PCB design of this AF signal generator contains ICL8038 waveform generator, inverting and non-inverting amplifier stage, output buffer and 12V regulated power supply. All the above mentioned modules are integrat...