Friday, July 31, 2015

USB to 3.3V - 5V serial TTL adapter

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 minimum number of components.

In this module we incorporate 5V/3.3V voltage selector switch to avoid interface matching issues due to different voltage levels of main-board/MCU and serial TTL adapter.

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 CH340G all the other components in this project are standard through-hole type components and may not need any special soldering techniques for construction.

In prototyping we test this adapter successfully with several MCUs which including PIC18F452, PIC16F887, LPC2103, ATmega8, ATmega32 and STM32F103C8. The device driver for CH340G is available to download at Schematic and PCB design related to this project are available at

Wednesday, July 15, 2015

Soldering station to drive HAKKO 907 handles

HAKKO 907 is popular and commonly available soldering iron in 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 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 in 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.

Internal view of finished soldering station.

Once calibrated, we may be able to regulate temperature of the soldering iron between 210 °C to 450 °C. As shown in the photograph we construct our final version of soldering station in slightly modified old ATX power supply casing. For this entire project we spent only 25USD, which is roughly 3000LKR at the time of writing.

Schematic, PCB design and wiring diagrams related to this project are available to download at