Donald,
The most difficult part of your project is to find cost effective sensors.
What you generally see for a few hundred dollars have an LCD display of
their own and would be difficult to interface. Besides temperature,
everything else will require a solid cost effective solution which provides
some kind of output either voltage 0-5 VDC or 4-20mA or digital pulse.
Plenty of people have tried aquarium monitoring and it's the sensors that
are difficult to obtain cost effectively. I would make sure you get the
sensors and electronics worked out first, the software including OWFS is the
easy bit as its zero cost, besides your own time !
-----Original Message-----
From: Donald J. Organ IV [mailto:[EMAIL PROTECTED]
Sent: Thursday, November 13, 2008 7:31 AM
To: [email protected]
Subject: Re: [Owfs-developers] 4-20 ma loop
Sorry I am a bit of a noob when it comes to electronics...hopefully that
will change after/during this projects. Where exactly does the 250 ohm
resistor go??
----- Original Message -----
From: "Rob Conway" <[EMAIL PROTECTED]>
To: [email protected]
Sent: Wednesday, November 12, 2008 3:17:04 PM GMT -05:00 US/Canada Eastern
Subject: Re: [Owfs-developers] 4-20 ma loop
4-20mA is simply 1-5VDC if you place a 250 ohm resistor in the current loop.
Use the 1wire 4 channel a/d. Please not though that the resolution of the
A?D is not as specified. Its more like only 8 bit, I think the data sheet
states 10 or 12 bit, somebody else posted this comment as well, didn't
believe them at the time however I now believe its true. However for your
need you can get reasonable data for aqua use. I can get accuracy of
PH transmitter actual reading on the unit 6.51 1wire reading <(+/-)0.02
Conductivity actual reading 200us 1wire reading <(+/-)5
I need to sample the data a few times then average it to get a filtered
reading due to the resolution and you just have to make sure your scaling
is correct. i.e. ph transmitter is calibrated -4-20mA (1-5 VDC) for 5.5 -
7.5 pH thus you'll never get the accuracy if you had calibrated it for
0-14ph = 1-5VDC it would not provide an accurate reading
Donald BTW link for temp probe
http://img.photobucket.com/albums/v319/rjconway/1wire_temp-1.jpg
rob
.
-----Original Message-----
From: Donald J. Organ IV [mailto:[EMAIL PROTECTED]
Sent: Thursday, November 13, 2008 6:51 AM
To: owfs-developers
Subject: [Owfs-developers] 4-20 ma loop
We are looking to measure Ph and a couple of other things and have found
that we will need to setup a 4-10 ma loop can someone recommend a lost cost
solution to this??
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