In my previous mail, I wrote:
 > Face the non-coated sides 1mm apart and dip in
Please read this as 10mm or 1cm apart.

Sorry,
Mohit Mahajan,
www.BioZen.co.in


Mohit (Lists) wrote:
> Hello Joshua...
> 
> ------------------------------------------------------------
> 
> pH:
> Here in India, good quality glass pH sensors (or electrodes) are about 
> Rs. 1000-1200 (~US$25). They haven't any temperature compensation 
> built-in but then since you are measuring temperature, you could do the 
> compensation in software. These sensors behave like very weak cells, 
> producing about 60mV per pH away from 7pH.
> 
> In a 7.0pH solution the electrode will produce 0V. So:
> In an 8.0 pH solution, the sensor = -59.7mV
> In a 6.0 pH solution, the sensor = +59.7mV
> and so on...
> 
> Read the sensor using a high input impedance JFET Op-Amp like the LF356. 
> Another quad op-amp to level shift the pH readings to something readable 
> by a PIC (0.5-4.5V <=> 0-14pH). To calibrate the pH reader, you get 4.0, 
> 7.0, 9.2, 10.0 pH tablets or solutions in all educational supply shops. 
> Try: www.carolina.com or www.wardsci.com if in US.
> ------------------------------------------------------------
> 
> Conductivity:
> Get small two small plates of SS316L, 10mmx10mm. Coat one side of each 
> with something non-conductive electrically, like  epoxy. Face the 
> non-coated sides 1mm apart and dip in water/solutions. You get a 
> 2-electrode home-made conductivity sensor.
> 
> Now check out this site:
> http://members.tele2.nl/rsetteur/aquarium/karel/colorie/english.htm
> http://tinyurl.com/yey6e8x
> ------------------------------------------------------------
> 
> Dissolved Oxygen:
> Unfortunately, this is going to be expensive as sensors themselves are 
> quite expensive. There are two kinds of 'chemical' DO sensors: 
> Polarographic and Galvanic. I suggest galvanic. They output current in 
> microamperes, which can be read by an instrumentation amplifier like the 
> INA111. The electronics is pretty straightforward after this.
> ------------------------------------------------------------
> 
> Temperature:
> RTD, thermocouple, silicon, thermistors, lots of choice and circuits 
> easily available on Google.
> ------------------------------------------------------------
> 
> Hope this helps,
> Mohit Mahajan.
> 
> Joshua Shriver wrote:
>> I'm starting a project to create an outdoor environmental recorder as a
>> hobby. Looking for water sensor recommendations that can be used with 
>> PIC's
>> for data gathering and interfacing with a SBC.
>>
>> Prefer to keep the costs down as much as possible; so far the few sensors
>> I've found (pH, temperature, conductivity, dissolved oxygen) have been
>> extremely expensive ($300-700 each).
>>
>> Any tips or ideas? Might be to expensive for a hobby project.
>>
>> -Josh
> 
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist