Multiple temp/humidity sensors

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1

Hi again ! (another noob question…)

Now, I try to find how much temp/humidity sensors i can connect to a mainboard… I’m thinking of a home/building automation system with sensors in each room so 10 or 20 can be realistic.

It seems it’s on I2C bus (so chaining seems to be possible…) but according to Sensirion datasheet, it seems it’s a proprietary protocol…
So multiple sensors on a i2C bus is possible or just only one ??

Best regards

SENSEI

2

results of a google request for maximum addresses i2c

http://www.societyofrobots.com/member_tutorials/book/export/html/35

3

The Gadgeteer temp/humidity module?

If so, then it’s an X or Y socket device. That means it’s not an I2C device, and therefore you won’t be able to have multiple of them.

If you don’t really care about local humidity, why not just look at a set of DS18B20’s for temperature?

4

Bear in mind also that I2C is has a pretty terrible physical layer for long distances…

5

I know that I2C works for long distances, but if i need temp + humidity, have I a choice in I2C or 1 wire ??

if not, is there a way to add expansions sockets to a motherboard to increase the number of sockets X or Y to put one temp/humidity module in each ??

6

I don’t think you’re going to get I2C running all over the house. Personally I’d make each room have a tiny board with the smallest available $0.69 PIC w/ an RS485 level converter ($1-2). You can use the internal oscillator on the PIC and your part count will be very low.

7

These modules are X or Y modules - meaning they use raw GPIO pins, not a bus, so you can’t share them. I guess you could connect them to a DL40 with custom firmware to handle that, as one option. But if you look at the driver, I suspect they’re not really very friendly (I haven’t looked; I’m just going from memory about the old community discussion about getting them working in the first place).

I personally think local humidity isn’t going to be highly variable, and I’d go with the easy 1-wire option (which is dead easy to use as a bus, and works over long distances). One “head” unit running it all, sensors everywhere. But there are other options, as others have said you can use a low cost/pin count device of your choosing and program it in native C and report back somehow. The Cerb40 is one other option, certainly it’s a higher cost option but it means you don’t need to step away from C# and netmf if you’re not comfortable doing so

8

brett,

you’re right, 1-wire is a good option. What humidity sensor should you recommend to use ?

9

I would use one of the modules we’ve talked about, right next to your central board. Then I’d just use remote temperature 1-wire devices from DS18B20 family. Sorry, don’t know of a decent priced 1-wire humidity sensor, and humidity doesn’t rock my boat. Hobby Boards is the 1-wire mecca, http://www.hobby-boards.com/ so you might find something there (although make sure you’re sitting down when you look)… you will notice that they basically take a non one-wire sensor and put it on a board with a one-wire controller; you’re free to design your own too if you choose.