March 27th, 2009

ATmega with SD card

ATmega with SD card

I was looking for quite a time to interface the SD card and avr’s in my projects, fortunately here is this demonstrative project which can be a good starting point for anybody who needs to store large amounts of data. By implementing the FAT32 file system the stored data can be accessed directly from any PC, without the micro controller interface. This is very useful since you don’t have to carry a laptop or the entire data logger around.

The project is well documented, it really gives the insight needed to understand the FAT32 system and how SD card work, the authors project has serial interface so the SD card can be accessed trough the Hyperterminal. The Atmega8 might be short in memory for the advanced FAT32 handling, so for the actual device it is recommended about 32K flash capacity controller.

Just imagine, instead of the I2C 32kbyte external eeprom you can have 1G storage capacity, and with the FAT32 system you won’t need the serial interface, usually used to download the stored data.

ATmega with SD card: [link]

March 24th, 2009

Compact 64 pixel display

Compact 64 pixel display

This is probably the most compact led matrix display ever, you need the ATtiny2313 and 88 Led matrix and off course two AA batteries for power. The micro controller is on the back of the display, soldered directly to the pins, since the voltage of two AA cells is around 3V you don’t need the current limiting resistors either. Just remember to use the low voltage type of micro controller like the ATTINY2313V-10PU the ATTINY2313-20PU won’t work, and in case of powering from 5V put some 100Ohm resistors in series with the leds.

This project can be easily adapted to other controller or display, but the ATtiny2313 and the LEDMS88R’s pin configuration fit together perfectly, no need for wire bridges to match the right pins.

With the 64 pixels you can’t display complex messages but there is enough resolution to achieve some eye catching animations, and the battery will last for two weeks. The size can be further reduced if you use small, coin shaped lithium cells instead of the bulky AA batteries.

Compact 64 pixel display: [link]

March 22nd, 2009

Asus Eee PC car charger

Since I often find myself on the road with my battery drained out and because I intend to use my Eee Pc together with a GPS module as a navigation system I thought it would be a good idea to make myself a car charger. The charger would have to output 9,5 V 2.5A, and it would have to be able to maintain the output voltage constant over variations of the input voltage. Of-course there are lots of voltage regulators these days that would fit my circuit, but I chose to use the LM2576 because such a charger has already been build and tested here (also featured on Youritronics here).

Here is the schematic of the charger:

Eee Pc charger schematic

After ordering the needed parts I noticed that the  inductor is slightly bigger than I expected it to be, so fitting the board into a small box became a bit of a problem. But I managed to designed the board so that it fits into the chosen box. I also fitted a medium sized TO-220 radiator so the circuit would dissipate the heat even in continuous use of the charger. The pcb was made using the photo etching technique and I tried spraying it with a mix of colophonium and alcohol that would act as a soldermask. The result is not pretty but I hope it will protect my board from corrosion.

EeePc charger pcb

After the soldermask dried it was only a matter of minutes until I assembled and tested it. The charger works great, the output voltage remains constant over continuous variations of the input voltage. Now all I have to do is close the box, solder a cigar lighter connector and pack it into my arm rest compartment.

Asus eee pc car charger

March 19th, 2009

Wearable POV unit

Wearable POV unit

In one of my previous post I presented a simpe handheld POV device, it was a little bulky not really suited for a true handheld device. If you are interested of building a similar gadget this is the thing you need, small enough to be mounted under your wrist watch and has a mercury switch to synchronize the display to the movement.

The entire project is open hardware, even the gerber files are available, very nice indeed. Although the pcb’s will be hard to replicate because of the small size and smd components, but not impossible.

My choice would be to redesign the pcb for an ankle mounted POV, that way the pcb could get bigger, there will be room for larger batteries, and if you make two of them you can use it instead of ankle weights when jogging or at fitness trainings.

Wearable POV unit: [via] [link]

March 18th, 2009

Arduino MEGAshield

Arduino MEGAshield

The Arduino Mega shield isn’t available yet and already NKC popped a shield for it, this is great news because you can rely on the well known support and flexibility of the previous Arduino boards.

As you can see on the picture, this is basically a prototype shield with only the reset button mounted and since no SMD pads available, no complex circuitry will fit to this board. The enthusiasts looking for testing the real power of the Mega Arduino will probably have to wait until a matching, powerful shield is available.

Arduino MEGAshield: [link]



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