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RE: [PSUBS-MAILIST] Electronic help request
Oops, I see the link now. I was too focused on your video : )
Steve
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Sunday, October 23, 2011 12:12 AM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Electronic help request
Hello folks,
I'm looking for some electronic debugging help. I'm using an Arduino UNO
board to interface some sensors with an LCD display. I currently have two
LM34 temperature sensors and a 0-1000psia sensor attached to the board. The
LM34 sensors are working fine but I'm having a problem with what I call
"drift" with the ADC readings from the pressure sensor. I've created a
video diary to help explain the problem and also show the hardware I'm using
at http://www.youtube.com/watch?v=uDpafXob2ko
Non-electronic types might be interested in viewing the video as well just
to see the project.
Arduino UNO
16 digital outputs
10bit ADC (1024 steps)
6 analog inputs
5vdc output
3.3vdc output
ground
PSIA Pressure Sensor
8-30vdc input voltage
1-5vdc output voltage
1v output at 0psi
Data-Sheet at the following web address:
http://www.ssitechnologies.com/PDF/Application%20Notes/PS_AN2_MediaSensor_P5
1_Product_Overview.pdf
The UNO board runs at 5vdc and I have powered the LM34 sensors directly from
the board. However the pressure sensor requires 8-30vdc so I have to power
that with a separate supply and have been using a laptop AC/DC adapter that
is putting out (steadily) 18.72vdc. Note that the following description
applies to the pressure sensor sitting on a workbench with steady
atmospheric pressure.
I connected the output from the pressure sensor to an analog input of the
board and observed a pretty large drift of about 10 steps. I measured the
output of the pressure sensor with a volt-meter and it was rock-steady at
1.050 volts the entire time. I did some internet searching and came across
this document
http://www.maxim-ic.com/app-notes/index.mvp/id/3775 which in Figure 2 seems
to suggest that connecting ground from the sensor to the ADC. So I ran a
wire from the sensor ground to the ground terminal on the UNO board which
smoothed out the ADC drift quite a bit dropping it to about
3 steps. The ADC will occasionally still produce a reading that is 8-10
steps high but that is the exception now.
Given that the pressure sensor is putting out a steady and unchanging
1.05vdc I cannot account for the ADC drift I'm seeing. I also do not think
the problem is with the ADC on the board because the LM34 sensors are being
read steadily with no step drift at all.
Is the drift caused by noise of some kind? Is it the external power supply?
Something else?
Any help appreciated.
Jon
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Weare, NH 03281
603-529-1100
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