posted at

alt.binaries.schematics.electronic

two halves

John Walton wrote:

posted at

alt.binaries.schematics.electronic

two halves

Hi John, that's very interesting. I found the hysteresis
problem is due to the speed of my windows based software.
In short I'm very lucky to get 520 samples sec which does flatten
but not eliminate the hysteresis entirely out of a MAX186
(multiplexed device).

There is Linux software that is supposed to run things
very fast that I'll have to also try out
As I'm not inclined to buy or scratch build a new
DAC board I'll try slowly ramping up the V by charging a
capacitor which should be slow enough.

To Alan and Chuck, I hooked my prototype to my
CRO set up for X-Y and it gave a nice clean curve when
viewed that way so it looks like capacitances are not an issue
at the 50Hz I'm using.

regards
Mark Harriss

I needed the controller to do other stuff than just manage the ADC. we
stayed with the Stamp since it is very easy to program for newbies. (but it
is rather expensive for a one-off project.) besides, Parallax paid for
developing the software. a PIC like the 16F871 (6 10 bit ADC's) is around
$6.00.

as I said, I have the DATAQ units and will be working with them at some
point. of course, one of the small problems with these self-incorporated
units is that the voltage references aren't going to be remotely as good as
something made from discretes. there is so much noise in tube stuff it
probably doesn't matter, however.

jack

"Mark Harriss" wrote in message
...
John Walton wrote:

posted at

alt.binaries.schematics.electronic

two halves

Hi John, that's very interesting. I found the hysteresis
problem is due to the speed of my windows based software.
In short I'm very lucky to get 520 samples sec which does flatten
but not eliminate the hysteresis entirely out of a MAX186
(multiplexed device).

There is Linux software that is supposed to run things
very fast that I'll have to also try out
As I'm not inclined to buy or scratch build a new
DAC board I'll try slowly ramping up the V by charging a
capacitor which should be slow enough.

To Alan and Chuck, I hooked my prototype to my
CRO set up for X-Y and it gave a nice clean curve when
viewed that way so it looks like capacitances are not an issue
at the 50Hz I'm using.

regards
Mark Harriss

Hi Mark,

Then I would say the problem is related to the time delay
between reading the X and the Y signal. The longer the delay,
the more the later read signal is skewed from its actual position.

The effect always occurs, but is more noticable in the steeply
rising sections of the curves.

If you are reading X first, then Y:

When you move to the right, the measured Y will be higher in voltage
than the acthal Y.

When you move to the left, the measured Y will be lower in voltage
than the actual Y.

This causes the looping. It is the same thing that causes the looping
in a totally analog curve tracer, only capacitance is what causes the
delay in the displayed value vs the value that should be displayed.

-Chuck Harris


Mark Harriss wrote:
John Walton wrote:


posted at

alt.binaries.schematics.electronic

two halves


Hi John, that's very interesting. I found the hysteresis
problem is due to the speed of my windows based software.
In short I'm very lucky to get 520 samples sec which does flatten
but not eliminate the hysteresis entirely out of a MAX186
(multiplexed device).

There is Linux software that is supposed to run things
very fast that I'll have to also try out
As I'm not inclined to buy or scratch build a new
DAC board I'll try slowly ramping up the V by charging a
capacitor which should be slow enough.

To Alan and Chuck, I hooked my prototype to my
CRO set up for X-Y and it gave a nice clean curve when
viewed that way so it looks like capacitances are not an issue
at the 50Hz I'm using.

regards
Mark Harriss