Embedded projects from around the web

AVR programmer is small as finger tip

admin — Fri, 24 May 2013 12:59:47 +0000

I don’t know if very tiny tools like programmer adapters are very handy to use, but it is always fun to watch how tiny they can get. Philip took a vusbtiny programmer and squeeze it in to smallest PCB he could make.

So, he made USB connector directly on PCB by tracing pads on it. But to be sure, on other side he made footprint for Mini USB socket. If one fails there is a way out. Of course all parts are SMD except the 6-pin ISP connector. The board size come to be 12mm x 28mm and I think, there still is a space to squeeze a bit by making ISP header smaller (use 1mm instead of 2.54mm) or choosing smaller passives instead of 0805. But would such tool be normally useable?

Attiny13 based RFID reader

admin — Thu, 23 May 2013 11:44:48 +0000

RFID readers aren’t very expensive to buy. But if you are real hobbyist and like building instead of purchasing stuff, then Attiny13 based RFID reader might be interesting to experiment with. It was build by Vassilis Serasidis – author of many great projects. As always he tries to keep things simple, cheap and easy to follow. The RFID reader he builds works with standard 125kHz tags that uses EM4100 protocol.

There is a good explanation on how the circuit works in physical level. It includes how reader transmits data and receives from passive tag. Reader is assembled on prototyping board using through hole components and hand made coil on the back. You will also get some understanding how to calibrate coil to have great range and reliability. Currently reader outputs the 10-digit Tag serial number via Serial interface 2400 bps 8N1.

Cat feeder uses Archimedes screw

admin — Wed, 22 May 2013 12:18:57 +0000

Normally DIY cat feeders uses simple dispenser. This works great, but it is hard to predict the amount of food that drops in to dish. Mgrenonville started with dispenser based feeder and now introduces second version which is more controllable and predictable. The feeder is controlled by Arduino with proto-shield attached. Time is kept using DS1307 RTC board. And feeder is run with screwdriver motor.

There is also an LCD screen where status can be seen. A serial interface is used to modify settings like time, number of feeds and other. Most fun part in this is screw feeder. It is made of Poly-morph which has low melting temperature and is fairly easy to work with. Feeder seems to work pretty smooth and is well blended above cat dish.

Smart power controller for Raspberry Pi

admin — Tue, 21 May 2013 09:50:46 +0000

One of the weakest sides of raspberry Pi is its power supply. We only get micro-USB option for powering the device. In one hand this is great feature because micro-USB chargers are becoming standard for phone chargers, so most of us already have those near by. There is another option of powering Raspberry Pi – using PGIO where you can find power pins. The real problem is that you don’t have much of power control on board – even there is no power button. Once you plug the adapter it starts to work immediately and powers off once you plug it off.

Felix Rusu have designed small power controller for Raspberry Pi which gives some control. It is Attiny based board so called ATXRaspi that gives features like power button, status LED, and link to RasPi. This allows shutting down the board without need to log in. when you click the power button adapter sends command to Raspberry Pu through GPIO to initiate shutdown script and will safely turn it off. Practically you can place any commands to execute before turning off – saving data, cleanup, writing to log files and so on.

Classical example of dot LED matrix display control

admin — Mon, 20 May 2013 09:33:29 +0000

Dot LED matrix is great for displaying various type information including graphical, text, and animation. They usually are big enough to see from a distance and bright to be visible at day and night. Embedded-lab built LED matrix display board which uses five 8×8 LED modules that makes pretty decent 8×40 display.

The display is clocked using PIC16F1847 microcontroller. Of course MCU doesn’t have enough I/Os to drive 320 LEDs. For this a cascading shift registers 74HC595 are used. One for every matrix module column. The rows are controlled with single ULN2803 which sinks LED outputs. Messages can be sent via serial interface using 8×5 byte array totaling the 320 bits. Each bit represents weather corresponding LED is ON or OFF. Received data is stored in to EEPROM memory, so after display powerup it automatically loads saved data and starts displaying without need of computer.