I want to "connect" two Arduinos, without using wires. The range is ~0.2 miles (300 meters). Using Google, I saw too many options.

The idea is to build something like a beacon, so the bandwidth can be small. I want to send 32 or 64 bits/second of data (32 bits for the application + 32 bits for checksum if the module does not guarantee consistency of data). The communication between Arduinos is bi-directional, and I'm looking for something cheaper than 50 US dollars per module.

Can I use a serial WiFi module for this, without using a router? Do you recommend a 2.4GHz module? Or a RF module?

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    They are all good possibilities, In order to identify a good choice you have to first define what you want to do. You've answered no useful questions that would narrow the choices besides distance. What bandwidth? what is your acceptable error rate? what price? bi directional or not? uniquely addressable or not? etc. etc. First define what you want to do then find the right solution – crasic Aug 21 '15 at 2:00
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    Might want to look into zigbee, they are expensive but tends have a decent range. – evolutionizer Aug 21 '15 at 6:24

I can highly recommend these cheap little 433Mhz radios. You can get them on amazon, ebay, etc. and they work pretty well for me. Your distances are a bit longer than my situation but I have to go through several walls.

  • From the picture I see that one (the transmitter ?) seems to have an adjustable coil. But even if it does, the other (the receiver?) doesn't seem to be adjustable. Is there some other way to avoid interference from colocated pairs? – Igor Stoppa Aug 21 '15 at 7:17
  • However, from the reviews, the max distance for reliable transmission seems to be much less, about 100m. – Igor Stoppa Aug 21 '15 at 7:20
  • The type of antenna will have a big impact on range. I've managed 50' with a simple length of wire using the 433 MHz radios. A directional antenna should be able to provide a gain of 5 at least. I considered implementing a CSMA/CD protocol but lost interest at some point. I did implement a Master with multiple Slaves solution. The idea was for a thermostat that could poll slaves with a temp sensor. Each slave had a unique 'address' the master sends a message with the slave's address and a command ('send temp') and waits for a response. – linhartr22 Aug 27 '15 at 21:07

It's a bit unorthodox solution, but have you considered toy walkie-talkies? They cover the distance you reported, even if some obstacles are in the path and they are relatively cheap, if you go for some sales. It requires a bit of hacking to connect the arduino to the mic/speaker and the push button, but it shouldn't be too difficult.

  • My idea isn't use a microphone. Instead, I want to send "digital" data, created by an application, and parse it from the reciever device. ¿There is any way to use the walkie talkies chipset for that? – Imaky Aug 21 '15 at 14:15
  • @Nullpo: there is no such a thing as a digital signal, it's all analog. It's up to the consumer of the signal to treat it as analog or digital. In other words: the walkie talkie doesn't care if you transmit voice or a sequence of 1 and 0, as long as the input voltage in within the same range as the voltage provided by the microphone. And the same goes on the receiving end: the arduino that receives doesn't care that the Walkie talkie thinks it's transmitting voice, as long as the voltage levels are compatible. – Igor Stoppa Aug 21 '15 at 15:29
  • To clarify further, what I'm proposing is to remove the microphone and interface directly the Arduino with the board in the walkie talkie. – Igor Stoppa Aug 21 '15 at 15:31

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