1. One or two displays directly to the i/o’s
2. One display with a 74LS247
3. Two displays with a 74HC595 and two 74LS247
1. Two displays with a 74LS247 and 2 i/o’s
2. Two displays with a 74HC595 and 2 NPN/PNP *
3. With a special driver IC e.g. MAX7219
Controlling two displays:
There are several possibilities to connect a 7-segments LED display to a microcontroller.
Directly to the i/o’s of the microcontroller, or a more economic way, with a shift-register e.g. the 74HC595 and multiplex the displays. With a shift register you only need 3 i/o’s and you have 8 outputs. Another possibility is the 74LS247 a BCD -> 7-segments driver IC, this takes 4 i/o’s. The diagram shows two 7-segments LED displays controlled by only 5 i/o’s. Ofcourse you can add more displays. With a minimum of components you’re able to control a maximum of displays. The circuit consumes about 20 mA with TDSL-5160 (Vishay) 7-segments LED displays.
Download: upcounter.hex and upcounter.eep
For more detail: Controlling 7-segments LED displays using AVR microcontroller