Replacement motor driver for mini drills

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 examining all the components, I concluded that the problem is in this MCU.

Damaged MG1502.2 motor driver.

Because the MCU is unknown, I decided to create my own controller to drive this drill. Due to limited space, I choose PIC12F series MCU for this controller. I used this MCU for zero-crossing detection, determine TRIAC firing times and to handle buttons and switches.

New PIC12F629 based motor speed controller

To drive the motor I choose BT134-600 TRIAC. The controller's supply comes from the mains through a simple RCD circuit. With the help of the inbuilt peripherals of PIC12F629 MCU, I build this controller with few external components.

The firmware of this controller is design to operate with 4MHz internal-oscillator of the MCU.

AC line waveform on minimal speed setting.

AC line waveform on maximum speed setting.

To design the PCB, I refer to the dimensions of the original controller board. To reduce installation problems I also placed all switches and connectors in the corresponding places as original board.

This controller board is powered by AC mains voltage. Avoid touching the board when power is applied. If possible, use an isolation transformer for the testing.

Installed driver PCB.

After installing this controller drill start to work again. The lowest speed which I set in firmware is not much use with the load. Besides that, this controller works as similar to the original controller.

View of the final assembly.

The schematic, PCB design files, firmware source code and compiled binaries related to this project are available at my GitHub repository.

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