(long introduction, sorry, the question is at the end)
I am playing with the AVR Dragon and seven segments displays. I habe builded all the circuitery for the 7-seg displays, and it is working fine with an external power source.
I am using cathode common displays and NPN transistors to work as switches, that will connect the common pin of the display to the GND of my power source when I put a 5v signal on the base of the transistor. Then I have the terminals of the displays connected to the +Vcc of my power source, and I am abble to light the segments.
OK, so far so good, but I have not used the AVR Dragon yet. My problem is the following:
When using the AVR Dragon with an Atmega32, I will have one pin connected to the base of the transitor. Other pins will be connected to the terminals of the displays. With that, the GND of the external power source will be used on the emiter termal of the transistor (it will reach the common terminal of the display when I put a high signal at the AVR pin connected to it), and other pin of the AVR will have a high signal to light a segment of the display.
Ok, after this long introduction my question is:
What do I do with the +Vcc pin of my external power souce? Can I just let it disconnected? Must I connect it to one of the Vcc pins of the Dragon? Must I use my external power source to power the Atmega?
Dunno if my text is confusing, hope you can understand what my problem is. Please help, I am afraid I can damage something by just trying the three options above :P