Remote sensors!!

[clone]

OK!  I want to have a photoresistor in one room, and send its resistance reading to my arduino board in another room via radio waves..   any idea on how to attempt this??

basically i want to be able to see on my computer screen the temperature of another room! 

[pomprocker]

X10 home automation can do this

[clone]

yea but i want to be able to do it with 5$ worth of parts.. thats the beauty of building ur own electronics.. they are cheap as hell!

[cosminprund]

The beauty of making your own electronics is that.. well.. you're making your own electronics  Commercially available electronics will allmost always be cheaper, better looking and more reliable. Just an example: for about $25 you can buy a cheap weather station that has a wireless temperature sensor you're supposed to place outside the house, a nice large LCD, clock, alarm, barometer, humidity sensor.

Back to your problem. First of all you're not going to have a photoresistor, maybe an thermistor - unless you want to know if the light is on in the other room. Next you're going to need something to transmit the temperature over radio waves and something to receive it. I doubt you know how to make your own radio, so you're going to buy radio transmitters and receiver ICs. That's where your problems start: If you buy an hobby-type transmitter it's going to be more then $5 by itself. If you buy from an general electronics shop (like farnel.com) you'll only find surface-mount RF IC's! (example: farnel has 121 types of RF ICs, all of them SMD). And that's just about the beginning... Shipping alone will be more then $5, unless you find stuff locally. And if you do find stuff locally, you'd better go by bike, cause the bus ticket might be $5...

I'm not saying don't do it, I'm just challenging your motivation. And your price range

[clone]

the photoresistor / thermister example was just an example...
what i plan to do is actually more complex..   and that is remote environmental control and monitoring of a greenhouse...  So, i want to be able to remotely see what the temp / humidity is in my greenhouse, also check water levels of reservoirs... and control pumps / fans / lights based on that information...... remotely!!  Doing it with wires connected is just too simple

[cosminprund]

Have you decided if you're going to have an microcontroller on the SENDING side? From your original post I gather you'll be using an microcontroller (the Arduino) but you're not saying how you're planing to do things on the sending side. This is a crucial decision in selecting the components for both the remote radio sender and your Arduino based radio receiver.

If you want to use an MCU with your temperature sensor you'd be able to select one of those 1-Wire DS18S20 sensor, cheap and easy. You'll also be able to use one of the wireless communication things discussed on this forum: XBee, Bluetooth;

Good luck

[chelmi]

You will probably need to use a micro controller on the sensor side.
Then you can use a cheap radio link like this one:
http://www.sparkfun.com/commerce/product_info.php?products_id=8950
and
http://www.sparkfun.com/commerce/product_info.php?products_id=8946

Note that this is a simplex link (one-way).

[clone]

sweet... those cheap radio transmitters / recievers look like they will do the trick!!

So.. i guess i should have an arduino board with transmitter / reciever on each end.. that way i can recieve temperature data from the sensor, and then transmit signals back to activate fans or other devices.

[cosminprund]

Getting close but no, that's not how you do it. The cheap radio transmitters you've been linked to are ONE WAY transmitters! And you did notice the link was to a receiver, you also need an transmitter (two parts). Sending sensor data from one Arduino to an other Arduino so the second Arduino processes the data and sends commands back to the first Arduino doesn't make any sense! Why can't the first Arduino include all the logic? The Arduino that has the sensors connected to it should be able to controll all that's there to be controlled, and only send status updates to the other Arduino to be displayed on a LCD. If the transmission fails nothing bad would happen, the second Arduino (the one in the house) would simply display old data!

If you want to give the Arduino in the house the ability to controll the one in the green house (ie: give it manual override commands like start that heater now, or open that window, or stop that water pump) then you'll (again) need transceivers, not receiver+transmitter (ie: both Arduinos need to be able to send as well as receive data).

Here's a cost-saving suggestion: Skip the wireless transmission for now! Just get a three wire cable between the two Arduinos (TX/RX + GND) and do all your programming. When you're done programming and when you feel the solution is solid enough to move into the green house simply remove the cable and replace it with a transceivers pair (or transmitter + receiver if one way communication is enough). Working this way would be helpfull because it removes one point of failure from the initial design (the wireless serial link) and requires a lower upfront payment. If you allready have two Arduinos all you need is an temperature sensor and the fun can begin!

[clone]

well... like i said in my previous post, i guess it wasnt clear... but my plan was to have an arduino board with a transmitter AND a reciever in both the green house and my house.. so... 2 arduino boards, 2 transmitters, 2 recievers.. that way the arduino in the house can send commands to devices in the greenhouse... and the arduino in the greenhouse simply sends sensory data such as temperature to the arduino in the main house.  yes, the arduino in the greenhouse COULD do all the logic by itself... but i want that manual override option available.. such as to change the operating function of the arduino in the greenhouse FROM the main house.

For example, raise the temperature by 2 degrees without having to enter the greenhouse.

[cosminprund]

I perfectly understood what you said, it's just that in my opinion it's the wrong approach. What I suggested would decrease the points of failure: Have the Arduino in the green house run all the logic and have the Arduino in-house run the human interface alone. If you absolutely want the Arduino in-house to change the mode of operation that's fine, but have it send the commands to the Arduino in the green-house! This eliminates an point of failure because the Arduino in the green-house can run the green-house even if the other Arduino fails for some reason! This doesn't stop you from changing the settings from the in-house Arduino! If you want to increase the temperature by two degrees, just send the greenhose-based Arduino the instruction to do so.

Besides eliminating the point of failure this approach will improve power efficiency: the two Arduinos would only talk to each other when they have to, not once every second to update sensor values and then send commands, make sure the commands are being executed etc...

About the wireless transmitters: IF you want the two-way communication, you buy transceivers, not two separate pairs of transmitters+receivers. If you do the latter (buy two separate pairs of transmitters+receivers) you're asking for trouble, because you'd be creating your own radio interference!

About the wires vs wireless serial connections: I suggested replacing the wireless transmitters with wires as a temporary solution. There's no difference between programming serial communication over wires vs programming serial communications over the wireless connection. This would simply delay the acquisition of the wireless modules, allowing you to make some progress. It would also aid with debugging: Unless you're an genius you're going to make mistakes and your two Arduinos would not talk to each other. If you've got wires between the two you know for sure it's the software. If you've got wireless in between it might be software, it might an miss-configured wireless module, it might an miss-wired wireless module: how do you debug when you've got 3 possible points of failure? (6 points of faillure if you count both Arduinos )

At the end of the day it's your project, you'll do it your way on your budget.

[clone]

uh.. yea.. my way WAS to have the greenhouse arduino run mostly on its own.. just being updated by the in-house arduino when needed... 
for instance, i already have other areas of the greenhouse run completely on seperate sytems.. for instance, my resevoirs right now automatically keep themselves topped up using a 50 cent NAND gate..  i just want to be able to monitor that water level from inside my house.

but alas.. i think a simpler solution would be for me to buy the Bluetooth connected arduino board.  that way it cuts out ALOT of possible problems.. only downside is i dont get to really learn anything! which is the goal of attempting something more complicated..

i found this other forum which is more specifically aimed at arduino board users.. i think i'll follow up this question on that board, as they might have a more specific answer for me. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl

thanks for the help cosmin!

[cosminprund]

Unless you're going to build your own radio you're not going to learn anything new by connecting an wireless adapter to your board anyway. I like bluetooth, I went with bluetooth myself because it's supported by new laptops out-of-the-box.