April 30th, 2009

Arduino Board Clone

Arduino board clone

Arduino based projects are very popular, because of its versatility, ease of operation and pretty large amount of projects available to be put into practice. This being said it’s not unexpected to see clones being made like the Coreduino.

Named like this because it uses the core of the Arduino board, the ATmega168 microcontroller and its oscillator components 16Mhz Xtal and the two 15pF capacitors. Coreduino’s PCB is smaller and can be easily connected to a breadboard. There are soldering bridges that let you power the board from ISP or USB. The programmers were built on separate PCBs and this way you can use the same programmer for many Coreduino boards. USB and Serial programmers are presented.

The USB programmer uses a FT232RL chip to convert data from USB to serial and send it to the ATmega. It can also power your Coreduino board and you can select the logic level to either 3.3V or 5V. The serial programmer has two level shifters made with discrete components and you can have RTS or DTR line to reset the Coreduino but you can not power the board with it.

In the project you will find all schematics and PCB layouts, everything you need to get it done.

Arduino Board Clone: [Link]

April 29th, 2009

AVR Object tracker

AVR Object tracker

Just the simple interfacing of camera with the micro controller sounds a lot of fun, then how about real time object tracking? This device has an amazing 27 fps speed and can track multiple objects which are defined by colors. The image sensor is OV6620 CMOS, and the brain is the ATmega8, trough the serial interface the user can download snapshots, configure the device or just view the tracked objects.

This project is an ideal start-up for those involved in robotics, by upgrading the basic IR based obstacle detection your robots gain a lot more freedom and intelligence.  Beside the amazing speed of execution the hardware is quite simple, my first thought was that the firmware is written in assembler I was surprised to see that the entire project is written in C. The PC program is in java and made available by the author, great way to get started with image processing methods and algorithms.

If you want to embed this project into your application the best way is to build it as is, and use a second controller for the other functions, since the tight synchronization needed between the atmega8 and the image sensor any other functionality would greatly reduce the image processing speed.

AVR Object tracker: [pdf] [download]

Network Controlled Outlet

A very interesting project showing you how to turn on and off the power from your mains outlet through computer network. It is very well documented and very useful. Basically you could turn on or off any device from any location as long as you can connect to your network.

The on/off switching will be done by an Olimex AVR/IO board. This board is equipped with an ATmega16 microcontroller (with no initial software loaded), four low-voltage inputs, a serial interface and four 5A/250V SPDT relays. These relays can be controlled by serial, by the four inputs or both depending on the code you will write for the microcontroller. So it is a very versatile board and only your imagination is the boundary of it’s utility.

The four low-voltage inputs are optocoupler isolated so this input can accept signals with different ground. Also these inputs are very helpful if you want to use a wireless module like the XBee. A PNP transistor is used to drive these inputs without any trouble.

Each relay provides connections for both normally open and normally closed positions. The relay will be placed between the hot wire that comes from wall and the hot wire that goes into the outlet. This way it will open or close the circuit on your command. Be careful however of the power consumption of the device you plug in the outlet. The relays are rated at 5A but they can be changed if your requirements ask for it.

The network controller is the Atmel NGW100 and will allow you to control the Olimex board through the network. It has two ethernet ports, lots of GPIO ports and Linux with TCP/IP installed. Control of the GPIO ports can be a little tricky with the NGW100 but you will find the scripts in the project.

The next thing is to connect the NGW100 to the network. Once that is done you can access the NGW100 through the network and execute the scripts according to your desired action.

Controlling Mains Power Through Network: [Link][Via]

April 27th, 2009

Subwoofer Active Filter

Subwoofer active filter

Nowadays the LCD and plasma technologies have become pretty cheap and big screen TV’s are more affordable. But your movie experience isn’t complete without good sound. DIY is a very good solution for a home theater speaker setup and subwoofers are the easiest component to build. Once you found a good speaker driver and made a cabinet according to it’s parameters all you need to do is give it a place in the whole system.

Active filters are the best solution to integrate the subwoofer in the HT. This way you add more control, flexibility and you eliminate negative influences of passive filters. The above circuit offers a very simple but effective solution. Using only a handful of electronic components cost is very low. The filter, as it is presented, has two main stages. The first stage, using half of the TL072 IC, sums the “left” and “right” channel into a single channel. By varying R3 you can adjust the gain.

The next stage forms the filter itself. It is a second order filter with 12db/octave slope. The corner frequency is set by the values of R5&7 between approximately 20Hz and 100Hz. You will need to set this frequency to match the other speakers, room and placement. If you don’t have any measuring equipment than trial and error is the way to go. Now there is one more thing you can do to make it really good. If you look at the first stage you will see that the signal will be 180 degrees shifted in phase. This may or may not affect your sound, it really depends on your room and speaker placement. However it would be good to add one simple inverter stage before the filter with gain set to 1 and with a bypass switch. This way you can select 0 or 180 degrees phase shift.

Subwoofer Active Filter: [Link]


A friend of mine asked me take a look at his power supply, because suddenly it stopped working. Of course I said yes, and the first thing to check after I removed it’s top, was the fuse. The fuse was wrapped inside heat shrinking tube which made the checking a bit difficult. After peeling some of the shrinking tube I was able to measure it’s continuity and find out that it was blown. At that time I hoped this was the only problem, I replaced it and powered the supply, but my joy was short, because the new fuse was blown too.

Obviously the problem needed further investigation, so I went along and checked the rectifier bridge, which was ok. The capacitors looked ok, so the next thing I had to check was the two switching transistors. To do that I had to remove the hole radiator which contained more than the transistors. Checking the transistors gave me the answer to the problem, because I found both to be broken. But now a new problem was raised when trying to find replacements for the two transistors 2SC3320. I was only able to find these in stores across US and China and both of these places would make the shipping and tax costs to high to be worth buying from there.


Now I have only two options, one is for someone to have a broken power source that has these same transistors, and that they’re still working, and the other is to find a replacement for these transistors, which I tried but with no luck. I wasn’t able to find another transistor to match it’s characteristics.

This is the datasheet of the 2SC3320 transistor. If you have any ideas on how I could solve this, please comment.

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