Electronic business card / scroll display. 85 SMD 0805 led’s matrix display, Atmega88V uController, and couple of other smd parts. Dimensions are 24mm x 85mm, supplied from 3V small coin battery. It will work for long time, even on discharged battery (2V). After button is pressed, device is waking-up from power-down mode and start scrolling text equivalent to pressed button. 4 text’s are saved in eeprom memory, each one can be 127 character length (128 cell is used for holding special end-char).
There are couple of options, you can access them by holding buttons:
1 – scroll speed (slower/faster)
2 – text in negative/positive
3 – change all displayed small letters to big ones
4 – text editor, after entering press one of buttons to select text to edit. Then, B1 is for previous character, B2 is for next character, B3 is for skip to next cell, after pressing that button previous character is saved. There is no need to use all 127 memory, press B4 to end edit, it will save last character, put special end-char, and go back to normal mode.
In normal mode, during scrolling text, pressing the same button will pause scroll and pressing again release pause. Pressing other button will cause immediately smooth skip to new text. After all text has been scrolled, device go to power-down mode and charge only 1uA from battery. When displaying, it measures battery voltage and calculates pwm for software leds current limiting, accepted voltage from 2V to 3.5V. Above that, increased current may damage leds. Below that, device can work even from 1.8V (used 2V red leds). On top side of pcb you must connect 3 led rows with thin winding wire. Fusebits: Internal 8MHz generator, and make sure to disable watchdog and brown-out which suck about 20uA in power-down.
Source code included, it need some improvements.
DOWNLOAD – eagle 5.4.0 project files, firmware HEX, BIN, source BAS, PDF schematics and pcb.