Dilshan R Jayakody’s Web Log

A few years back I purchased Honeywell CL15AE evaporative air cooler and it is15L indoor air cooler manufactured by JMATEK (for Honeywell). Sine last week this cooler became dead, and the only thing which I can see live is its red color power indicator. After disassembling the unit I see that most of the components of the controller PCB are rusted and damaged.  As I observed the main reason for corrosion is the absence of protective varnish on the top side of the PCB. The original control board of CL15AE cooler. At first, I restore all the damaged parts in the PCB with new parts, which including SS8050 , SS8550 , transistors and a few of electrolytic capacitors. After replacing those components, the unit starts to beep during power up but failed to power on. Damaged SS8050 and SS8550 transistors. After some tests, I figured out the problem is in SONiX SN8P2602 8-bit microcontroller.  Due to unavailability of microcontroller and it's firmware I decided to pr...

Simple NTP clock is a maintenance-free clock application developed to work on single-board computers like Raspberry Pi , Orange Pi , etc. This clock application uses the Simple Network Time Protocol (SNTP) to get the time and display it on seven segment display which I designed . This application is designed to work on most of the Linux based systems and had minimum dependencies with system libraries and peripherals. I developed this application to work with Allwinner H2 Plus based Orange Pi Zero board, but this can compile for other platforms without doing any modifications on the source code. NTP clock on Orange Pi Zero. To compile this application issue the following commands: make clean make Parameters related to this application are available at config.json file. This file can be used to specify the NTP server, time zone, and display module port. The source code of this project is available at github.com .

This project is about an open source, USB based, 10 digit seven segment display unit. This unit is specifically designed to work with POS systems and banking applications. Initially, this system is developed to work with PC based systems, and later it was modified to work with other platforms and applications. Final view of the USB seven segment display module To simplify the communication interface this unit is designed to emulate a COM port in the host terminal. Because of this feature, this module can work with many systems without having any additional device driver(s). To extend the scope of this unit, it also comes with an option to switch between " direct mode " and " API mode ". In " direct mode " application or host device can directly send characters to the display unit over the emulated serial communication channel. The " API mode " is intended to provide more extensive features with this unit. All the " API mode ...

The 1750Hz tone bursts are often used to trigger repeaters. There are several methods to build 1750Hz tone generators which including TC5082 divider , using MCUs, etc. In this post, I present another 1750Hz tone generator which I built using 74HC4060 high-speed 14-stage binary ripple counter and 7.168MHz crystal. In this design, 74HC4060 is used to drive the crystal and divide its output by 4096. By using 7.168MHz crystal, this circuit produces 1750.0Hz square wave output with a 50% duty cycle. A prototype version of the 1750Hz tone generator. This circuit is extremely simple to build, and I construct my prototype using a breadboard. I tested this generator by connecting its output to my Baofeng UV-5R handheld transceiver and it gives an excellent result. The key motivation to build this generator using 74HC4060 is, because of its common availability. Most of the tone generators which I found on the internet are built using MCUs or by using rare ICs, because of that rea...

Dual-tone multi-frequency ( DTMF ) is a common signaling system used in telephone networks and other communication devices. It uses a mixture of two sine waves to generate tones which represent ten digits, the letters A to D , and the symbols # and * . While I’m examining other Arduino based DTMF generators I noticed most of the designs are based on Holtek HT9200 DTMF generator IC. After a couple of experiments, I figure out that Arduino itself is capable enough to generate DTMF tones without using any external IC or generator. Prototype assembly of the ladder circuit. The design which I explained in this article is based on R-2R ladder DAC. I did this design using Arduino Uno board and still this library support only for this board. But it can easily extend to other AVR MCU based Arduino boards. Schematic of the DTMF generator. The R-2R ladder is attached to the PORTD of the MCU which is Digital out 0 to 7 in Arduino Uno board. In this design, I used 100 Ω and ...

TFA9842AJ is quiet old 7.5W audio power amplifier introduced by NXP . This amplifier IC is no longer produced by NXP, but still, it's available to purchase in many places, which including eBay , AliExpress , Amazon , etc. NXP TFA9842AJ Power amplifier IC. I tested a couple of TFA9842AJ based amplifiers in the last couple of years. The main reason I liked TFA9842AJ is its simple, clean design, wide operating voltage, and high-quality bass-rich audio output. Thanks to it's built-in DC volume control circuit this audio amplifier can easily interface with MCU. In this article, we provide a generic TFA9842AJ module which works with most of Arduino boards, MCUs and SOCs. Schematic of the TFA9842AJ module. As illustrated above, this system consists of LM321 operational amplifier and TFA9842AJ IC. To support both 5V and 3.3V logic inputs we introduce logical level selection jumper ( J2 ) into this design. To control the volume PWM input must apply to the J1 . In this...

In my workshop, I got a couple of INGCO power tools. INGCO is a Chinese power tool manufacturer, and this brand is quite popular in Sri Lanka. Out of those tools I frequently used INGCO MG1502.2 mini drill. I purchased this drill three years back and mainly use for engraving and for precision drilling. A few days ago while I'm using this drill, it suddenly stopped. As a first thing, I checked brushes and mains-lead. After a few minutes of inspections, I found out that both brushes and mains lead are in perfect order. To further examine I decided to open the drill. The internal layout of this drill is quite simple. It mainly consists of an AC motor and electronic speed controller circuit. After a few checkups, I determined that the electronic speed controller is dead. In speed controller board I notice some unknown microcontroller, 74HC595 shift register, and Z0409MF TRIAC. As like many Chinese products here also they erased the IC number and other markings of the MCU. After ...