Re: Re: DAC-80s (was FS: Lots of IC's)

On Fri, 23 May 2003 21:20:51 -0400, "Tom McClintock" <tomm@mgcap.com> wrote:

>>From what I've been following on eBay, all the different
>flavors of DAC-80-Vs have been selling for upwards of $10
>each. Many are being purchased by chip suppliers
>themselves. And the occasional David Fish ;)
>
>The DAC-80-Is typically don't sell for more than $1-$2
>each. Presumably a small hack could be made to use the
>current versions?

It can be done, but it's a little complicated.

You need to run the output of the current DAC into a resistor to ground, this
does the current to voltage conversion (ohms law). You then need to buffer this
resistor using an op-amp. Since the value of the resistor directly effects the
voltage, assuming the current is constant (ohms law, again), you need the op-amp
to keep from loading the resistor.

But there's more...

Cinematronics used an origin of 0,0 in the lower left corner of the screen, even
though vector monitors all have their electrical origin in the center of the
screen (no current through the yokes = 0,0). The DAC-80-V allows access to the
feedback of the internal op-amp to allow voltage shifts and gain control. You
will have to add the same offsets to your new op-amp to be compatible with the
original DAC-80-V circuitry, in order to move the origin to the lower left
corner of the screen. The gain of the op-amp will have to be adjusted (along
with the value of the current to voltage resistor) to set the voltage levels to
the same as those coming out of the original DAC-80-V.

If someone was interested in building these daughter boards (not me), I could
come up with a schematic for a DAC-80-I board. I could also come up with a
schematic using more modern 12 bit parallel DACs. The problem is that in
onesies and twosies the modern parallel DACs are usually in the teens of
dollars, making it more economical to simply find someone selling the DAC-80-V.

-Zonn

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Received on Sat May 24 11:17:40 2003