January 31st, 2009

XBee power monitor

xbee power monitor

The XBee devices are based on the ZigBee protocol, which was developed for short range wireless communication, especially for home automation systems, this project is a perfect example for its designed purpose. The device is a smart socket, which measures the momentary power consumption and sends it to a host or server, which logs the data for further use. Although the measuring device used is bought as is, and doesn’t has any switching element so you can’t switch off the load remotely.

The real potential of XBee isn’t even scratched with this project, so feel free to improve the original idea, the smart outlet is a great idea, but beside the monitoring some control functions should be added.

With the analog inputs and digital outputs including two PWM channels of the XBee it would be easy to build more advanced loggers or home automation systems without micro controller, the software runs on the PC and the XBee acts like hardware interface.

XBee power monitor: [Link]

January 30th, 2009

Wireless bootloader for AVR

wireless bootloader for avr

Have you ever been annoyed by the fact that you mounted the pcb and needed to update the firmware? Dismantle everything, connect to the programmer or just to the serial cable if you have bootloader installed already, not to mention if your hardware controls some power device like a motor, then you need to be careful not to fry your PC’s serial interface or the motherboard, the solution is simple and available, use a wireless connection.

The guys from Sparkfun made a robust and yet compact communication protocol which can be used via wireless link to download the firmware, they use the XBee module which is a Zigbee to serial converter, they mounted the XBee on to the usb to serial converter board and there you have it, simple and robust wireless link which can be used also for debug purposes. The bootloader is written in C, and the PC program in visual basic, the XBee modules can be replaced with any wireless solution, I will most certainly try it with some bluetooth modules.

Wireless bootloader for AVR: [Link]

January 29th, 2009

Advanced LED display board

Advanced LED display

Like I promised earlier, this is a solution for larger LED displays, with as few as possible pin costs, my solution uses only 7 micro controller pins, and controls 128 LED’s, this can be scaled up to 2048-4096 without problems (check the schematic).


The heart of the schematic is a simple serial to parallel conversion, in other words a shift register (IC1,IC2) this can be connected directly to the SPI of the ATmega88, or to any SPI master. To further optimize the pin count I used a 3 to 8 decoder (IC3), since only one row is powered at any given time there is no use to directly connect the rows to micro controller pins. The schematic contains also the power buffer, which is made with discrete transistors, basically this is also a row to column addressing solution, to prevent the LED’s from flashing when the shift registers are updated the row’s must be disabled for a short time, this can be made with LEN input (IC6 pin6).

Example of a sequence: disable the rows, by pulling LEN to logic 0, update the shit registers via SPI, select the row, enable the row by setting LEN to logic 1. Between the row updates it is usefull to place a delay, makes no sense to have a refresh with a few kHz, this makes the display ligth fade, if the delay is to large the image won’t be steady, you must experiment the optimum refresh rate, my advice is that 50Hz-100Hz of image refresh is enough, this result in 400-800Hz row refresh.

By inserting more shift registers or decoders the resolution of the display can be increased, the only limit is the refresh rate, if you have a large display and you want to make some complicated animation which need a lot of computing and considering also the SPI frequency, the refresh rate could became to slow and the display will flicker.

Advanced LED display board.

January 28th, 2009

Monome with Arduino

Arduino monome

First of all for those who don’t know, the monome is a music controller which is used to generate sound effects, is has a lot of push buttons which have different color back lights to generate a visual effect to. DJ’s VJ’s use the commercial version, but there are also available DIY kits, open source open hardware designs, the most simple is to use the Arduino with the monome shield, but you can build your custom shield or entire system.

The basic functions are, use a large keyboard matrix, with back lit buttons and based on the sequence which the user pushes the keyboard generate a MIDI output which is interpreted by a mixer or synthethizer.

The sound and visual effects can be customized if you build your own monome, most of the parts can be bought from Sparkfun, including the pcb’s, although there are open source projects, the programming part is not for beginners and you need some external MIDI interpreter which can be expensive.

Monome with Arduino: [Link]

January 27th, 2009

Analog display reinvented

Analog display reinvented

Nowadays everybody is using LCD’s, OLED’s, TFT’s to display information, this project is almost a gadget since it uses analog meter gauges to show the time, off course you can display other stuff to, like Internet connection speed, or your stock status, check the link for details.

The hardware is based on Arduino, but you can use it as a starting point to adapt to your favorite controller, for the displays you can use the commonly used 0-20mA or the 0-10V gauges with customized back plane, if you choose the 0-20mA type than a voltage to current circuit is needed, if you use the 0-10V type then a voltage amplifier with a gain of 2. In both cases you use the PWM outputs to make the Digital to Analog Conversion (DAC) and one op-amp to adapt the 0-5V to the meter gauge.

Analog display reinvented: [via] [Link]

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