MaxCoderz

I'm working on a project for my school and I have a very very strange issue. I'm using a micro controller to drive a small car, and as an added feature, we've set up a turret on the top that can fire BBs. We've decided, in honor or retro, to control this turret using an NES controller, with the only real drawback being that we have to run around behind the car because we can't find a wireless NES controller, on account of they never made one.

</rant>

Anywho, I've got the microcontroller communicating with the NES contoller fairly well. the problem is, it only works when I have the data line for the NES controller hooked up to an oscilloscope. If I take that out and try to run it, I get no signal from the controller. To my knowledge, an oscilloscope is not supposed to interfere with the connections, only monitor them. I will admit that I do not know enough to really say that with any certainty. The end result is that when we try to run the car without looking at the lines, it behaves as though we aren't pushing any buttons.

Has anyone ever run into a problem like this before? It's so odd, because we put a lot of work into getting this far. Is there perhaps something that the oscilloscope is providing to my circuit that I am failing to reproduce?

I can send pictures if necessary, but I'm afraid it will be a smidgeon difficult to get a schematic up without help, I don't pretend to know how to draw one.

Thanks a bunch, this is veeery strange.

-thegamefreak

Could the problem be power related?

We have considered this, as we've got a strange power setup to begin with. The Microcontroller on the car has a power supply, and the NES has its own. I don't *think* we were crossing between the two, but it's difficult to know, I'll have to check on it tomorrow. If I had it set up like I think, they were sharing a ground, which now that I think about it might have done strange things. I guess I get to send a picture tomorrow, as I'm not entirely sure what's happening.

-thegamefreak

I'm not sure why NES controllers are so popular for this sort of thing, as they do overcomplicate the issue somewhat (most other joypads of the era were just switches in boxes rather than having exotic control circuitry in them). Anyhow...

The two circuits should share a common 0V, and the voltage that the NES controller is outputting (and running from) should roughly match that of the microcontroller. I don't know how the NES controller signals to the NES itself, but you should have a pull up or pull down resistor on the microcontroller's input. I can't really suggest much more without a schematic, I'm afraid.