Author Topic: Sensors Logged to Remote Webserver with Control Feedback  (Read 2584 times)

Trick

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Sensors Logged to Remote Webserver with Control Feedback
« on: November 04, 2009, 09:49:08 AM »
Hi Folks,

Thought I'd post the details of my project at an early stage in case I learnt anything useful along the way, it might encourage me to share my findings!  I'm in the process of developing a prototype monitor and control unit.  Essentially it's job in life will be to log the averaged values from various sensors at five minute intervals, which are then HTTP POSTed to a remote webserver.  The webserver will then perform a few on the fly calculations and feedback any changes that should be carried out.

At the time of writing I have an SBC65EC with LCD2S and a PT01TC attached.  These are housed in an IP rated case (needs to be splash proof) along with four buttons and some other hardware for connecting sensors.  There will be three type K thermocouples, plus a pH probe and ORP probe.

As this project isn't really orientated around the webserver built into the SBC, everything needs to be driven from the push buttons and LCD display.  So far I have a basic menu system working (ref: http://forum.modtronix.com/index.php?topic=1229.0) and one stable thermocouple amplifier.

It's been pretty smooth running so far, the main effort really required in getting used to C, I'm more accustomed to higher level languages which has made me very lazy! Here's a quick summary of what I have learnt on the electronics side of things thus far:

  • If you are going to use the ADC, forget using the internal voltage reference. It appears to be exceptionally noisy so IMO is next to useless if you require any degree of accuracy and/or stability.
  • As you are going to the trouble of setting up an external voltage reference, then use the opportunity to alter the ADC's scale.  In my case for example, even after amplification the voltages will still be less than 1v, so I have chosen that as my reference voltage to get the best resolution.  This is the weak part of my peripherial circuitry at this point, as I've cobbled together a poor quality potential divider and smoothing capacitor, which still isn't good enough IMO.
  • A valuable trick (although new to me) is to use the excellent 7660S chip to provide you with a negative power supply right off the VCC pin of the SBC.  I have made a small veroboard with a few spare rows for +5v/0v/-5v, so I'm good to go with any amplifier ICs I need elsewhere.

I'll be posting as I go on Twitter, but will update things here from time to time.  Any constructive criticism always welcome, I'm quite happy to stand corrected when I get things wrong!

Regards,

Richard.
Follow my project on Twitter: http://twitter.com/richardwvm