Tobi's Corner » 7 segment http://tobiscorner.floery.net ... the electronix portal Tue, 22 Jun 2010 06:54:22 +0000 en hourly 1 http://wordpress.org/?v=3.0 Big 7-segment Display Clock http://tobiscorner.floery.net/projects/avr/big-7-segment-display-clock/118 http://tobiscorner.floery.net/projects/avr/big-7-segment-display-clock/118#comments Wed, 19 Mar 2008 08:28:32 +0000 theFloe http://tobiscorner.floery.net/?p=118 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.

Display in action see the digits schematics ]]> http://tobiscorner.floery.net/projects/avr/big-7-segment-display-clock/118/feed 4