Backyard Aquaponics
A place to discuss aquaponics

nice work, thats good to know

I just started playing around last night with a lm335. I have a ds18b20 here as well which is working easily enough that i should be able to chech the lm335 with once i work out how to best use it for the temp ranges we would be after. Fun fun

The DS18B20 looks interesting.
Not done any 1-wire stuff, might have to try to get hold of some.
Wonder if you could ground it at the remote end, rod in the ground...
That would be great, run a single wire round the system and multi-drop the sensors.

If you are trying to save running a cable out, they can be parasitic and pull their power from the data line. I have never done this though and im not sure what is involved.

Yes but they need a ground wire too, so its' 2 wire not 1 in reality.
I was wondering if you could ground the device remotely with a ground rod.
If it's not too far it should work, but you can get large potential differences doing that, potentially blowing the device or the controller.
Parasitic devices just steal some power from the data line when it's high.
The nice thing about this device is you can multi-drop and the output is digital with each device having a unique identifier code in it freeing up the ADC inputs for something else.
I feel a trip to town coming on

and without a ground wire you are going to get TONS of noise i think. I would be surprised if it worked at all....ground voltage differences are baaaaaad...

But each device would be grounded locally, so noise shouldn't be an issue.
But yeah ground voltage differences can be high enough to kill, probably safer to run 2 wires lol.

DS18B20 - there had to be a downside, 210Baht each, $7.
More than the micro !

Wow! thats alot. I am fairly sure you can get some free samples, but you wont get many. That probable explains why i only have 1 ds18b20 and 3 or 4 lm335's. lol

If the earths are not at the same potential the chips wont communicate to the PC. Running the earth through the ground would be like adding a resistor to the ground pin and then say biasing it by some arbitrary voltage. If it was more than a few volts difference they wouldn't talk at all.
Its possible, just need to fix the voltage difference.
Something like this perhaps

http://www.rtaautomation.com/support/435NBx/app_note/index.html

I have a handful of similar 1-wire temp chips lying around...that I probably wont use I went nuts with the free sample thing when I was at uni

could use some optoisolators too..

I fairly went nuts too when i was at tafe. Although my supplies are slowly dwindling

Depending on the type of wiring they use for the house, your neutral could be earthed. It is here. With wet ground would you not get close enough?

Hey dui! I've told you, try this site.
http://www.es.co.th/detail.asp?Prod=06700549

This is cheapest hobbyist can buy, pay online, deliver via post office of thailand.

I check a few items.
This site is about 1/4 of your price.

The DS18B20 (and associated models) are nice little units. Have a look on flea-bay and you can probably find them cheaper.

The only thing you have to watch out for with parasitic power is that it limits the cable length to around 100m (both according to the spec sheet, as well as practically). You can go further, but then you need active power.

Not a big issue, just something to keep in mind.

I agree with SuperVeg on ground issue.
Ground rod is more expensive than wire and is not movable.
I think ground rod will not work for DC, especially on low Voltage.
Your 2 rods, sensor and controller, will act like capacitor then you will have different ground level.