Dilshan R Jayakody’s Web Log

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...