Re: Cinematronics > Atari Adapter???

On Mon, 14 Oct 2002 02:38:47 -0500, Rodger Boots <rlboots@cedar-rapids.net>
wrote:

>You could use something like the DAC7541 which is under $11 even in
>single lots. The op-amp following the DAC will determine the settling
>time. Like Tom says, you can have the DAC only give a positive output
>(in this case by using a negative reference for the DAC) to allow cheap
>switches and subtract out the midpoint (using the same reference voltage
>for best results) to get the desired output swing.

Well, actually, Tom was quoting me. But on the subject of analog switches, the
Space Fortress did something a bit clever. They used a 4066 to switch bi-polar
voltages by driving it's GND pin negative. I think they used a -6v supply for
the GND pin, and something above 6v for the positive side. I don't have the
schematic in front of me, but they used something like a open collector
transistor to level shift the inputs to the 4066 so they would also appear to be
between -6 to +6 volt.

By shifting the operation voltage down in respect to the rest of the circuit,
the 4066, which can handled 0-12v signals is now switching -6 to +6 volt
signals, which is fine since the voltage at this point are within +/- 3v.

On a similar note, I recently picked up one of those Japanese Star Castle clones
using this modified vector circuit (same as Space Fortress -- but there is
nothing anywhere on the game that says what the name of the game was. Weird.)

The vectors look like crap. It's impossible to line them up correctly. It's not
so bad that the game couldn't be operated, but nothing anywhere as clean as a
real Cine designed game.

I haven't looked into it (I've been *way* too busy to fix games.) But I'm
wondering, is this just me? Or do all Space Fortresses have poor vector
alignment? Anybody else own one of these things that would like to comment?

-Zonn
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Received on Mon Oct 14 13:31:55 2002