Tobi’s Corner

Arduino Interface to Sureelectronic’s 6432 Dot Matrix 5mm Red LED Display Information Board.

Download PDE:

• surematrix.pde

Inspired by http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/ I started to build a USB driven display. I ordered some big green 5×7 dotmatrix display from http://evilmadscience.com/ and had a look at v-usb.

What you get when combining those is a via USB controllable dotmatrix display. The PC related programming I did in Python using libusb and the python binding called pyusb. So the program should be cross platform compatible! Also python allows one to extend the functionality(e.g. checking for new mail, usb notifications of any type…) very easy.

Video after the break.

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What can you do with 100 common anode rgb leds? Build a 8×8 matrix and interface it!

The circuit uses 74HC595 shift registers with output latch. Each shiftregister interfaces one color + one shiftreg for the matrix rows. The interfaces uses 6 I/O lines for faster speed and easier interfacing. An AVR running at 8MHz can update the matrix with 8 brightness levels displaying nice fading colors patterns or colored text (or both). The sample program creates fading color patterns using a sine table. For smoother display a double buffer was implemented.

Download: rgbmatrix.c

For my 7-segment display AVR clock i was searching for a way to keep the clock accurate. One option would be using a DCF77 standard time receiver. The module I had seemed to be broken so I decided to use an ethernet interface and NTP. For this I purchased a small ENC28J60 + AVR board from Simon Küppers. This small board is only about 38x30mm in size and includes an ATMega168, ENC28J60, Ethernet-Jack + Magnetics and a voltage regulator. The 14 available I/O Pins are connected to a standard 0.1″ header, so there are possibilities to extend the board.

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I’ve bought some 14cm high red 7-segment LED Displays on EBay and started to build a clock based on AVR ATTiny2313.

The circuit is build with an AVR ATTiny2313 a UDN2982 high side and a ULN2803 low side driver/switch

The LED Module is powered with 18-20V to give a brighter display. The forward volatge of a single segment is about 13V. 13V + voltage loss at the switches (worst case 2V + 1.6V) is about 16.6V. I used 39Ohm resistors for the segments and so 16.6V + 39Ohm x 0.08A = 19.72V. Because of multiplexing 4 modules to get an avarage current of 20mA per segment the current has to be four times higher ( 20mA x 4 = 80mA ). The dots on the modules have a lower forward voltage resulting in a higher limiting resistor: (16.6V – 3.6V – 3.6V) / 80mA = 120Ohms.