hi there, I thought I would post this question as I am currently looking at purchasing some sensors. If anyone can help with good prices for air temp, relative humidity, electrical conductivity (in solution),PH, co2, ambient light, water level sensors that would be fantastic!
I'm a fan of Parallax. They sell reliable, easy to use stuff... and all of it has data sheets.
Air Temp ($4):
http://www.parallax.com/Store/Sensors/TemperatureHumidity/tabid/174/CategoryID/49/List/0/SortField/0/Level/a/ProductID/87/Default.aspx
Humidity ($5):
http://www.parallax.com/Store/Sensors/TemperatureHumidity/tabid/174/CategoryID/49/List/0/SortField/0/Level/a/ProductID/554/Default.aspx
or, temp and humidity in one sensor ($36):
http://www.parallax.com/Store/Sensors/TemperatureHumidity/tabid/174/CategoryID/49/List/0/SortField/0/Level/a/ProductID/94/Default.aspx
Electrical conductivity? Not sure I've seen a sensor for that?
PH? What ever happened to the good old Litmus Test? I can't think of any sensors that do that, just paper tests.
CO2 sensor with breakout board... currently out of stock ($36):
http://www.parallax.com/Store/Sensors/GasSensors/tabid/843/CategoryID/91/List/0/SortField/0/Level/a/ProductID/598/Default.aspx
Ambient Light ($15):
http://www.parallax.com/Store/Sensors/ColorLight/tabid/175/CategoryID/50/List/0/SortField/0/Level/a/ProductID/176/Default.aspx
Water level... look at the beaker?
That's the best list I can do for you... and it's only one shipping charge. I don't work for Parallax or anything, just really like their sensors (not so much the Stamp Basic). Oh and as a note, that CO2 sensor doesn't give you a reading, you set it up to trip an alarm when a threshold is exceeded and it'll let you know by sending signal high off it's alarm pin. You will also need to calibrate the sensor yourself. I've never used the CO2 sensor, but I have used the CH4 sensor.
I am also a fan of Parallax - they also sell this:
http://www.parallax.com/Portals/0/Images/Prod/P/PropellerBlock-L.jpg
SparkFun is always adding new sensors:
Lefty
there are PH sensors, not looked but they used to be available for multimeters!
Typical glass pH probes generate extremely small signals. You must use an amplifier with the probe. Luckily there are many implementations out there to copy, just google "DIY pH meter" and the like.
Hmm... temp, humidity, EC, Ph, water level,
Will you also be using 110/220V relays for fans, lights, and water pump control?
Seriously if you source these parts and get something working together please come back here and share your results! I understand what you're working on. Cool project, best of luck.
I've not used them but have been browsing their site. Just throwing it for comparison.
They have most sensors you asked. There is a water sensor that might work for you.
I have their sonic ranger (excellent), temp+humidity sensor combo (pretty good), and a line sensor (still working on using it).
They also have relays.
They ship from Hong Kong, took 17 days to receive my order (US).
I am working on something very similar.
The pH phidget from phidgets.com converts a standard pH probe into a 0-5V signal : sweet !
As for EC Electrical Conductivity, I tried hard to look at building my own circuit for an inductive aka toroidal ec sensor, but the circuit is a bit difficult and a probe and station cost hundreds, even on ebay.
I was happy to find solumetrix, who sell serial-interface ec probes. I will post my arduino code for this in a separate thread (my first code contribution!). The probes are about 130GBP, which is steep, but if anyone can beat this in any way I am happy to learn. BTW, I have a Rosemount toroidal probe for sale from my earlier efforts.
Good luck !