13 Jun
2009
13 Jun
'09
4:36 a.m.
Gordon JC Pearce wrote:
That's because it uses the RC time constant to
measure the value of the
pot. It doesn't care about the voltage. You set the pin to output low
so you discharge the cap and then set it to be an input and time how
long it takes to go high again. The higher the pot value, the longer
the time.
The Cromemco D+7A card does use a ADC circuit composed of a DAC(1408),
SAR, and Opamp Comparator. It does care about the voltage. I have one of
the Cromemco JS-1 joysticks ( http://tinyurl.com/nqcbkm ) and plan on
duplicating this circuit too to make it compatible with existing
software. That method you described had been used on other micro's, such
as the Apple II and TRS80 mod.I to keep parts cost low.
=Dan
[ = http://www2.applegate.org/~ragooman/ ]