I need to make Arduinos communicate over long distances (at least 0-15m, but it would be great if I could make it work on 0-100m) keeping the cost as low as possible. My speed requirements are not too high - a few KB every few seconds.
I was thinking about connecting Arduino Leonardo's with USB cables, but I am not sure if Arduino can supply enough power to transmit over such long distances. Also I am not sure if they can communicate in peer to peer mode (normally USB is master slave mode). I am also not sure if USB is the right choice here and if the legends about 25m long usb cables are true....
I use a 433 mhz radio telemetry module for flying my quadcopters.
The are around $30 on ebay or hobby king and are basically just a serial port that is translated for you to 433 radio.
It simply has 5v gnd and RX TX pins on each end and as far as wiring and coding you pretend its nothing more than a serial connection. There is unlikely to be a simpler solution.
nivwusquorum:
keeping the cost as low as possible........
I am also not sure if USB is the right choice here and if the legends about 25m long usb cables are true....
I'm sure it isn't, and any legends you have heard probably aren't - they are more likely to be facts.
You might consider an NRF24 wireless link. If one of them is a high power module, I believe they are good for 100m. They are popular and well-supported on this forum.
I have used a cheapo JY-MCU blue tooth over 15m line-of-sight, but I would not recommend it. There are more powerful bluetooth devices, and I believe they are good for 100m, particularly bluetooth 4.
All of the above would probably be cheaper than USB, and very likely more practical. There are other competitive wireless devices.
If you want to use cable, you are probably better off using the standard serial communication with good quality network cable, it being made for the purpose and reasonably priced.
nivwusquorum:
Could you expand a bit on what do you mean by network cable?
Not really, it's usually blue
Ethernet, or some cheaper alternatives? Ethernet has 4 twisted pairs if I recall correctly - seems like a bit of an overkill for my needs.
CAT6 Ethernet cable. CAT6 is the standard stuff but CAT5 would surely suffice, and cost less if you can find it. The only thing that determines overkill is the cost. CAT6 is made for long-distance communication, comes in unsurprisingly long lengths, and is reasonably priced. There is no actual obligation to use all the wires but you might as well, and I understand most people do.
Clearly, there are cheaper alternatives like, I guess, bell or phone. I have heard of people having problems with cheap cable, me included, but I have never heard of people having problems with CAT cable.
Nothing 'wrong' with them.
They are just far from the simple transparent uart implementation. You cans save some money and deal with the things I like less about the ones you found including:
Custom Librarys
3.3 volts
documented difficulties with power supply
You will get them working and they will do what you want, however with the ones I suggested you have nothing to do but plug them in and they work like as simply as jumper wires on a breadboard.
If $ are important to your project, go with what you have found.
Personally I was happy to spend the $30 as I can reuse them over and over for different projects
Regarding the network cable, 100 meters is right on the edge of cat 5 cable run lengths so make sure to use cat 6.
100 Meters of cat 6 will cost you more than the $30 433 module though unless you buy it in a 305m box, even then pretty much gonna cost more.
I have the HC05 / HC06 bluetooth modules which seem to do the 15m most of the time but not a good idea as really pushing it.
Also, remember UART serial is not RS232.
It doesn't use the big voltages of RS232 and so is unlikely to want to do 100m. Pretty much sure it will handle the 15m, maybe even with normal non twisted pair wire which may be cheaper.
Maybe it will do fine, maybe you will have 100 of cable you cant do anything with?
One note, i forgot to mention, those 433 modules, the kit has a usb connection on one side!! You dont want that i suspect.
You would have to investigate if you could use two of the non usb module together.
Honestly, a mcp2561 Canbus tranciever is like 90 cents in singles and you can use it with normal serial, you don't exactly have to use the entire can protocol to use the can physical layer. People do it with i2c every once and a while.
Or, rs485 as the more common solution even though the cheap transceivers don't tend to be quite as cheap or as good last I checked.
Both of these are two wire bus protocols, meaning one device can talk at a time but all devices share one differential pair. Either one will be reliable.
Stay away from rs232 unless you need full duplex or you need to talk to existing equipment that uses it. It's old, the range isn't as good, the chips often need lots of extra capacitors tacked on to get the voltage up to the weird +-7v or whatever it uses, and since its not differential you will both make and receive more interference.
Use cat5 for the data, and the other 3 pairs can carry power or other stuff. If you parallel the conductors in cat5 to get more power yoursel you should fuse each individual wire and don't just use one fuse. because if one power wire breaks the others will have to take up the slack which could cause them to exceed their current rating.