Re: Apple II ADCs

[fl332@cleveland.Freenet.Edu (John L. Graham)]

Hmmm, let's see here...6 channels, twice, in 50 ms, sounds doable.
We actually make several variants on the same basic design. It 
started life as a somewhat standardized ADC design we incorporate
into different experimental systems (we work for a university
research institute). The 1200 baud serial system was just a real
simple system to build and would work for a lot of our applications
that fall into the single channel, 100 ms, and multiple channels 
every second or so, and 1200 baud is WAY overkill for that. Using a
straight 12 bit ADC (the trusty old AI-13) I was able to read a
single channel every 2.5 ms without even trying from AC/BASIC.
I talked to Doug Wolf (the hardware barins behind this) about
high speed applications and he thought the ADC we're using would
handle data acquisition rates of up to about 40 kHz (about one
reading every 25 us). I thought he said we could put a faster
serial chip on it (say 9600 baud) or for really high speed stuff
put a bit of RAM on the board so you could run it in a burst mode.
In this case you basically tell the board to go off and take
256 data points (for example) and come back when you're done.
Hmmm, come to think of it we run a system a LOT like this where
we're using a GS to control a boxcar integrator averager. The
boxcar doea all the work of collecting and averaging the data,
while the GS simply controls it over a serial line (the GS also
controls the firing of a pair of lasers using a modified CCS
counter/timer card). I'll see Doug at lunch today (Wed. is
pizza day) and I'll counce some ideas off him.

Have fun!

John

P.S. For other's information, and ADC is an Analog to Digital
Converter. It's a device that takes and analog signal (usually a
voltage) and converts it to a digital number a computer can read.
To make a LONG story short, it let's you record data from all
sorts of neat stuff. Every Apple II has a simple little ADC in
the game port which can read either 2 or four channels and convert
a _resistance_ to a number and using some really simple hardware
you can do all sort of neat stuff. More on that later :)

JLG