Well i am going to have to start from scratch.
I would have POT that would regulate 5 volts and i need to get it as
accurate as possible. The resolution of the the ADC should be 2^9=512,
which would give me a quantizes a voltage to .01Volts
Diagram:
POT ----> ADC converter Chip ----> BCD priority encoder -------->
Parallel port.
Does this make sense ?
Does he ADC need a frequency to operate. i am not sure because the ADC
would requires sample therefore by increasing the frequency you have
increasing the sample rate or can you get away without adding a
frequency to the IC ?
The problem with A/D-to-port schemes is usually that they
require a lot of tricky clocking schemes. For example, I
have an old (obsolete) Adnav port A/D that uses a MAX398
chip. But it sends its data out serially, so the port lines
have to be toggled laboriously to fetch each bit.
If you had a parallel output A/D you'd still need to do some
handshaking since the port normally wants to see only
8 bits at a time (though you can use the Status port to
gain extra bits).
If this is for a production application where you want to
keep the cost down, and you have a microcontroller
at your command, there are some pretty simple
dual-slope schemes. A single-slope scheme may be
all you need, however: Make a simple current source that can
charge a capacitor linearly. Feed the capacitor voltage to
one input of a comparator; the other input is the voltage
to be measured. The port must supply a line to short out
the capacitor (through a NPN transistor, say). When you
turn this line off, start a counter in the microprocessor.
When the comparator trips, it should cause an interrupt
whereupon you read the counter. Depending on the
charge rate of the capacitor and the internal counter
rate, you can get really high resolution from this simple
circuit. (A dual-slope is a bit more involved, but has
much better rejection of power-line harmonics if you
do it right.)
Hope this helps.
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
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