MAMEWorld Forums - EmuChat - Re: Analog emulation

> It's all about solving differential equations. Does Runge-Kutta mean anything to you?
> If it doesn't, you probably need to study some more.

Yes, I heard about it, but it's all too long ago to remember the details.

> Not just that, but you need to model the effective impedance of whatever's driving
> it. TTL circuits have far lower output impedance when the output is low than when
> it's high. Classic 4000 series CMOS outputs' current capacity varies with the input
> state. You also have to consider the characteristics of the input it's connected to.
> TTL inputs sense current flow - pulling them down switches on the multi-emitter
> transistor. CMOS inputs sense voltage, and look like a small capacitor to the driving
> circuit.

Well, first off CMOS isn't in my scope for now. Simulating with real values for voltages and currents isn't either. All I can do is make the most primitive assumption to how a capacitor acts at a specific time, and that is it's either conductive or it isn't.

I know you say that's wrong, and I know that myself, but I can't do much about it :-)

> > Diodes are conductive for one polarity, depending on how anode and cathode are
> > connected to other parts.
>
> No, they allow a small forward current to flow up to the bias voltage, at which point
> they allow far more current to flow. They allow a smaller reverse current to flow up
> to the Zener voltage, at which point they allow a much larger current to flow.

Yep, I remember that fairly well. However, it's the same case here: I have no voltages other than 0V and +5V and thus I don't calculate anything for a diode. I want to assume that a diode with anode tied to +5V passes the +5V to the part connected to the cathode. Or the other way round: the cathode tied to ground is passed to the part connected to the anode.

[networks]
> No, it wouldn't. You need to be able to deduce the differential equations for the
> voltages and currents, and solve them using numeric methods.

...if I want a SPICE like simulation of the circuit, yes.

[capacitors]
> Time delays won't cut it - you either black box it, or simulate it properly.

The disadvantage of black-boxing is that the schematics including any black-box doesn't match the original. That means I will have to go with 2 schematics per game: original and "digitalized".

> Seriously, go with black boxes, and consider studying circuit theory if you want to
> move to a more realistic model in the future.

I doubt I am able to do that. It would need a companion author who's willing to care about the analog part. I can create the editing functions and network lists for any format he'd desire, but I can't grok circuit theory in a moderate time frame.

Thanks for your comment!

Juergen