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...

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 ...

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...

While designing some mechanical projects we often have need for easy to build motor speed controllers. Thanks to the SGS-THOMSON Microelectronic’s TDA7274, now we have easy to build, low voltage D.C motor speed controller. TDA7274 provides wide operating voltage range from 1.8V to 6V and in this project we use it to drive small CD-ROM ejection motors. In this project we design entire speed controller with 39.3mm × 28.9mm PCB. While at the prototyping we test this system with 5V power source and successfully control several CD-ROM ejection motors, cassette motors and toy D.C motors. You can obtain all the circuit diagrams, PCB patterns and other information of low voltage motor speed controller from google drive .