pc based oscilloscope again

[uchwoody]

I've got a circuit diag now. But i want 2 modify it a bit.I found an Ic , a display driver whose only purpose is just to signal when voltage level changes polarity. I thought of replacing it with something else, maybe an opamp,or voltage comparator. What d'u think?
Also, there's another ic (7402 I think) that has a 9v line going in, and a 5v line coming out. It looks like a power ic of some sort, but I can't identify it. Anybody have an idea what it is?

[uchwoody]

I think I shd have used a different icon.
The power ic no is 7805(just that), it seems to have just 3 pins, one is 9v, the other is 5v, and 3 is common. The display driver is LM3914, I think it's used for a dot/bar display, cos it has output lines connected to leds.