Small toy with a 4*4 LED matrix using an AVR ATmega8 controller and 16 10mm LEDs available at www.conrad.de and www.reichelt.de
The matrix is driven in multiplex-mode.
In hardware-version 1.0 the LED-anodes of every row are connected to each other and via a current limiting resistor to a port-pin of the AVR (one row per pin). The cathodes of every column are connected to each other and the collector of a NPN-transistor. All emitters are connected to GND. The transistorís bases are connected thru current limiting resistors to AVR port-pins (one base/column per pin)
For Version 1.0. Done with avr-gcc and avr-libc:
For the hardware-version 2.0 N-channel FETs have been used as column-drivers and P-channel FETs for the ROWs. Much brighter now and current at the AVR-I/O-Pins is well below limit. Fade-in and -out have been added to the firmware. The source-code available for Version 1.0 has to be modified to reflect the inversion caused by the BS250 row-drivers. Additionaly a button has been added to switch Blinky on and off and to enable a "sleep-mode" with turns Blinky off after 20 minutes.
Firmware source for V2.0 is not available here, sorry.
Schematic for Version 2
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