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RE: [PSUBS-MAILIST] Electronic help request
Hi Jon!
A couple of comments...
First, you need a common ground throughout...all sensors and the adc must
share a common ground. If the pressure sensor measures 0-1000psi using an
output voltage range of 1-5 vdc, then that corresponds to a 4mv change for
every 1 psi. If you are trying to read pressure to within .1 psi then you
are looking for a change in voltage of .4 mv or .0004 volts. I'm sure your
volt meter doesn't display to that accuracy. You could very well have noise
on your sensor of ~.3 mv that you would never see on your volt meter and
which can account for your drift.
Now, you may ask where the noise would come from...digital electronics are
notoriously noisy due to square wave outputs that cause numerous harmonics
at higher frequencies. How do you improve this? Shielding of all analog
signals would be a start. Bypassing the sensor signal with a capacitor or
two would help filter out the noise but would also slightly slow down the
response of the sensor. A 10uf cap is way too big for high frequency
bypass...you need something more like .01uf or even .001uf.
I suspect you aren't seeing the same type of drift on your temperature
sensors is due to the range being much smaller than the 1000 psi range on
your pressure sensor. What I would recommend is to use a sensor with a
smaller range such as 0-300 psi. That would yield a better scale of
.013v/psi which would be a little less sensitive to induced noise.
Hope this helps somewhat....
Al
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Monday, October 24, 2011 10:00 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Electronic help request
Good point, although most of the small development I see happening is
being done just using the USB. However, you are correct that the specs
don't match the practice. I did check the 5v output from the board with
both the USB and a 12vdc battery and in both incidences it was 4.97v so
it didn't seem to matter.
Jon
On 10/24/2011 5:29 AM, Jens Laland wrote:
> Jon
>
> I now see that you're running the Arduino UNO board on 5 VDC, but this is
> outside the recommended voltage supply range for this unit, ref
>
> http://arduino.cc/en/Main/arduinoBoardUno
>
> Under the 'Power'-section it reads, quote
>
> "The board can operate on an external supply of 6 to 20 volts. IF SUPPLIED
> WITH LESS THAN 7V, however, the 5V pin MAY supply less than five volts and
> the BOARD MAY BE UNSTABLE. If using more than 12V, the voltage regulator
> may overheat and damage the board. The recommended range is 7 to 12
> volts."
>
> Could this be part of your problem?
>
> Best regards,
> Jens Laland
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