Whats the cheapest and easiest way to send data wirelessly between two Arduinos?

I'm planning on making a wireless weather station, and I need to send data between two Arduinos wirelessly. What's the cheapest and easiest way?

Inexpensive 315MHz/433 Hz Tx/Rx pair and VirtualWire library. Hardware is in $6 range for a set.

Well, it depends on how far apart the two Arduinos are, whether there is line of sight between the two (or if not, how much would the radio waves have to go through), are the Arduinos battery powered, how much data is going to be sent, whether you need to plan for error detection between the two Arduinos, and whether the communication needs to be 2 way.

At the simplest, might be line of sight using infrared LED/receiver (similar to a TV remote control), but I suspect this is not desirable for a weather station.

Above IR, might be 315Mhz/433Mhz receiver/transmitter pairs. You probably need to make sure you are getting the signal from your Arduino, and not something else using the same frequency.

Higher up would be something like mesh networking (look up xbee, zigbee, radioblock, etc.). With mesh, you can put intermediate mesh's up between the two Arduinos, and they would repeat the message.

Or bluetooth (be sure to get at least one board that can be the master).

If you need it to go further than bluetooth/mesh, and you have a home wifi setup, you might be looking at wifi.

If you need to connect world wide, you might need a gsm shield (but be sure to understand the costs associated with sending/receiving data for this one).

If the weather station is really in the boondocks, and you are rolling in money, I suspect there is a way to hook an Arduino to a satellite phone.

MichaelMeissner: Well, it depends on how far apart the two Arduinos are, ....

You left out really close: LED and a light sensor. Sort of like the IMP (which itself would be another alternative).

https://www.sparkfun.com/products/11395 http://electricimp.com/

lewtwo:

MichaelMeissner: Well, it depends on how far apart the two Arduinos are, ....

You left out really close: LED and a light sensor.

Yes, though to my way of thinking it is in the same class as IR. I can imagine other ways to transmit information (audible signal, something moving using a motion sensor, color sensor, using a puff of air, vibration sensor), but a lot would not work too well for the OP's weather station.

As they all state, the FIRST question is how much range?

Cheap BT modules, nRF2401, and basic XBees are good for about 10m [30 feet]. XBee Pros with 50mW output power are good for about 100m [300 feet] or so. There are also cheap radios like the RFM12 and RFM22 that operate at 433Mhz, and have range between 40m and 500m, but they're a lot more trouble to hookup, and the libraries for them tend to cause people a bucket load of grief [there are dozens of threads in the Networking section from people can't get the RFM12 to work].

oric_dan: basic XBees are good for about 10m [30 feet]

The specs for the low-power XBee ZB (S2) modules are 40m indoor/urban, 120m outdoor line-of-sight. Specs for XBee 802.15.4 (S1) modules are 30m and 90m.

This is obviously a situation where "YMMV" but my experience is that while those estimates might be towards the "best-case" end of the scale, an XBee that can only make 10m either has problems or is in a very, very difficult environment.

If you can open the window temporarily, one option might be to run a thin wire for the radio receiver, so that the receiver is just outside the window, but the computer is inside. That way you wouldn't have the glass between you and the weather station.

Assuming you can't put the receiver out the window, I suspect the distance and going through glass will probably eliminate the cheaper options. My guess is you probably are looking at wifi as your main option. Going through glass, using a visible light or IR based signaling is possible, but both of those can be subject to problems going through either bright sunlight or heavy rain.

There is OpenSourceRF that was a project I thought about backing last year in kickstarter (but ultimately did not back): http://www.opensourcerf.com/rfd21815-wireless-inventors-shield-for-arduino.html

Given your Arduino is powered by the wall power, using ethernet over power lines might be an option, but to set things up probably would be more expensive than wifi, as you would need two units, plus an ethernet adapter for the Arduino, and have to weatherproof the units.

MichaelMeissner:
I suspect the distance and going through glass will probably eliminate the cheaper options.

I’m not so sure. Those wireless key fobs for your car are basically the equivalent of the 315/433MHz license-free ISM band Tx/Rx modules, and those work from 15 feet through glass.

Unlike your car remote though, the cheap ISM modules really need proper antennas. The good news is, “proper” in this case is just one (quarter wavelength) or two (half-wave dipole) pieces of wire the right length.

If you have range issues with the cheap ISM modules, up the voltage (but don’t exceed the limit). Usually they accept up to 12v so running them on 5v or 3.3v can reduce the range.

[quote author=Jack Christensen link=topic=182388.msg1351648#msg1351648 date=1376392404]

oric_dan: basic XBees are good for about 10m [30 feet]

The specs for the low-power XBee ZB (S2) modules are 40m indoor/urban, 120m outdoor line-of-sight. Specs for XBee 802.15.4 (S1) modules are 30m and 90m.

This is obviously a situation where "YMMV" but my experience is that while those estimates might be towards the "best-case" end of the scale, an XBee that can only make 10m either has problems or is in a very, very difficult environment. [/quote] For whatever reason, the advertised ranges are always a good deal farther than anything I've ever gotten in practice, and I've tried a lot of different devices. My XBee S1s "always" faded out at 10m, just from room to room in the house - 1/4 wave whip.

I remember you getting a lot longer distance to your shed/weather-station/whatever, but I'm not sure that's a good general rule.

In regards glass, as mentioned, I got about 40m range LOS with the RFM12 (433 Mhz, 1mW output, whip), and could also receive the signal from inside the car, located about 20-25m away on the back side of the building (so transmission through several walls), just as long as I held the antenna next to the car window.

Going through glass, using a visible light or IR based signaling is possible

Visible light will get through the window but the IR is highly unlikely to especially since you seem to be talking 2-3 inches. Think greenhouse effect. Also if you have an IR camera try taking pictures through (normal) glass.

Greenhouse effect traps "heat", not necessarily near-IR "light". The former is more like 10um (10,000nm), the latter more like 800nm wavelength. Something to look up.

CDCosma: Will these be able to go through the glass window and about 20 feet? http://www.ebay.com/itm/NRF24L01-Wireless-Transceiver-Module-2-4G-SMA-Antenna-/130912545049?pt=LH_DefaultDomain_0&hash=item1e7afee919

The nRF2401 with PCB antenna get roughly 10m range, or a bit more with slower data rate. I believe those antennas shown are 1/2 wave dipoles, so I'd think you'd get somewhat better range.

Re glass, you might just have to test it and see.

Also, if you check some more, you'll find exactly the same modules (ie same header pin out) except with a PA, power amplifier, onboard for $15-20 range. Much better range.