mholling
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long-range wireless board

Wed Jul 17, 2013 11:26 am

Hi folks. This year I've been working on a remote, solar-powered webcam project using the Raspberry Pi and a nice 900MHz radio module from RFM, the DNT900. This radio has a reach of up to 40 miles and only costs $70.

I've ended up with a design for an interface board for the Raspberry Pi and the DNT900 radio. The board is called RPi900. It includes a sturdy power supply and real-time clock, and can remotely switch power to the Pi. There is also access to analog and digital I/O provided by the radio.

I wrote a driver for the radio so you can configure it easily, and talk to one radio or a whole network of them. Sending and receiving data is via the serial port. You can even set up a network connection for the remote Raspberry Pi using point-to-point protocol over the radio link.

The design is open source. I've put documentation at http://rpi900.com, as well as lots of tutorials for setting things up. I have had a batch of the boards made up and they are available to buy. Hopefully these may be of interest to some forum members!

-- Matthew

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malakai
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Re: long-range wireless board

Wed Jul 17, 2013 11:40 am

Wow that looks so nice atop the Pi.
http://www.raspians.com - always looking for content feel free to ask to have it posted. Or sign up and message me to become a contributor to the site. Raspians is not affiliated with the Raspberry Pi Foundation. (RPi's + You = Raspians)

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startrek.steve
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Re: long-range wireless board

Wed Jul 17, 2013 12:23 pm

40 miles range? How?
Line of sight at ground level is 5.9 miles.. 16.9 on a tenth story building..
Is it in a balloon?
Pi 2 running LibreElec Krypton, Pi 2 running Wheezy Desktop, Pi 1 headless Wheezy, downloading Radio, Pi 1 running Picore headless Media Server, Pi Zero to be an Old Time Radio Project. Pi 3 testing. Pi Zero W downloading Radio shows headless.

mholling
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Re: long-range wireless board

Wed Jul 17, 2013 12:48 pm

startrek.steve wrote:40 miles range? How?
Line of sight at ground level is 5.9 miles.. 16.9 on a tenth story building..
Is it in a balloon?
Yep you are correct, the 900MHz band is basically line-of-sight. The 40 mile figure is RFM's range specification for the radio. It would be possible to approach that line-of-sight distance if your remote site is several hundred metres higher, say a hilltop, or yes, a balloon!

Nonetheless, 900 MHz is known for fairly good obstacle penetration, e.g. trees, buildings. And of course it is license-free in many countries (US, Canada, Australia etc).
RPi900 - long-range wireless for Raspberry Pi.

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RaTTuS
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Re: long-range wireless board

Wed Jul 17, 2013 12:59 pm

900Mhz is not legal in the UK
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
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mholling
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Re: long-range wireless board

Wed Jul 17, 2013 2:16 pm

RaTTuS wrote:900Mhz is not legal in the UK
That's true. The DNT900 manual lists "US, Canada, South America, Israel, Australia and New Zealand" as license-free in 900 MHz.

RPi900 could also be used with the DNT2400, which is a pin-compatible 2.4 GHz version of the radio. 2.4 GHz should be legal to use in the UK, I think? The range would be less (claimed as 10 miles for the DNT2400).
RPi900 - long-range wireless for Raspberry Pi.

gwigga
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Re: long-range wireless board

Wed Jul 17, 2013 2:20 pm

mholling wrote:
RaTTuS wrote:900Mhz is not legal in the UK
That's true. The DNT900 manual lists "US, Canada, South America, Israel, Australia and New Zealand" as license-free in 900 MHz.

RPi900 could also be used with the DNT2400, which is a pin-compatible 2.4 GHz version of the radio. 2.4 GHz should be legal to use in the UK, I think? The range would be less (claimed as 10 miles for the DNT2400).
Did some searching and found the following link

http://www.fpvuk.org/things-explained/v ... s-for-fpv/

2.4Ghz specific
2.4Ghz video equipment is very popular. Its the most commonly made equipment and generally is the cheaper of all the bands to buy. It has good range / power ratio and is sought after by many.

Hip hip…………… Hang on………..
Yes you guessed it, there’s a problem. The problem with 2.4ghz is that with the launch of the Spektrum and Futaba 2.4ghz radio control equipment you cant use your 2.4ghz video equipment around any 2.4ghz radio user.
Their equipment will interfere with yours and spoil the picture being broadcast.
Another downside of the 2.4ghz video is it has poor object penetration properties and buildings trees and people can all have adverse effects even completely loosing picture.
So when you fly with 2.4ghz video you have to remain in Line Of Site to the plane.

SO so long as no ones flying anything close by we should be ok :lol:

now if they did The 5.8 Ghz band that would be good :@

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tzj
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Re: long-range wireless board

Wed Jul 17, 2013 3:28 pm

Excellent work! Tho I do have a feeling some people here in the UK will buy the 900mhz band modules to attempt the interception of phone calls, or phone companies just don't want us to use their masts as relays!

I'm still wanting to use VLF for short messages (bit-bashed) over very long distances, without interfering with naval clock signals.

The pi can transmit signals with an aerial/wire attached to the pwm out pin, but the issue is reciving signals... Would software pwm work?
http://www.themagpi.com <---- Checkout the MagPi
(The MagPi - Co-Founder)

badnu1s
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Re: long-range wireless board

Mon Oct 06, 2014 12:22 am

Matthew,

I am new to the raspberry pi and a ham radio operator who has experimented with spread spectrum in the past.

Given the low cost, I am thinking of getting 3x Raspberry Pis B+ and DNT900DK's to do some experimenting and learning.

Does your interface board now work with the model B+, or would I need to get an earlier model?

Best way to order your interface board and the DNT900DK's from the US?

Also, could you provide me with some guidance as to how you I ought to configure the DNT900DK's?

Piece of cake to use PPP for point to point with two of these, but I don't quite see how this would work in a star topology configuration. Would the master be configured as PPP server and all the remotes connect and route to it, with all the radios set the transparent mode?

Thanks,
Bernie

mholling
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Re: long-range wireless board

Mon Oct 06, 2014 10:46 pm

Bernie: unfortunately RPi900 won't work with the B+, due to the removal/relocation of the P5 header and mounting holes. You'd need a model B or model A. The model B (at least) should still available.

You only need the radio module itself (DNT900P) to use with RPi900. I usually get these from DigiKey. (Mouser and a few other places also have them.) RPi900 boards are available from http://rpi900.com

If you buy the manufacturer's DNT900 developer kit (DNT900DK), this includes two radio modules and two interface boards. You wouldn't need RPi900 boards in this case; you can plug each interface board into any Raspberry Pi (including B+) using the USB cable. The developer kit board appears as a standard USB-to-serial device and you can talk to the radio over /dev/ttyUSB0. The DNT900 line discipline I wrote works just as well with the developer kit boards over USB.

The main benefits of RPi900 are the compact form factor, and the on-board power supply, real-time clock, status lights, I/O connectors and remote shutdown circuit. Much smaller than a Raspberry Pi plus developer kit board; great for stuffing into a small outdoor enclosure.

As for software setup, I support Arch Linux and provide packages to set up PPP networking fairly quickly. This includes a star network topology (or point-to-multipoint, in DNT900 terminology). On the Raspberry Pi base station, each remote radio appears as a separate tty (/dev/ttyDNT0, /dev/ttyDNT1, etc). The base station establishes a PPP link to each remote over these ttys. It provides IP forwarding and proxy address resolution to the LAN (probably via ethernet). The end result is that the remote Raspberry Pis are connected to your LAN: you can SSH to them, serve data from them, whatever you want. See the RPi900 website for more detail on how to set this up (a few lines of configuration are all that's needed).

Feel free to email me if you need any more technical advice!
RPi900 - long-range wireless for Raspberry Pi.

badnu1s
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Re: long-range wireless board

Tue Oct 07, 2014 3:14 pm

Hi Matthew,

Thanks for your answer and also the suggestion of just using the development kit.
Now that I understand the real throughput of these radios (especially in point to multi-point), I don't think they'll work in the application.

Instead, I am thinking of going with low cost, 2.4 Ghz. Wifi dongles that are known to work with the raspberry pi and use babel to do mesh routing.

However, I am still interested in the dnt900 for long distance point to point internet links.
In the manual, it mentioned being able to synchronize multiple radios with different hopping patterns with a sync pulse, thus allowing me to set up parallel point to point links to increase the bandwidth (point to point).

Does your driver and the stock pppd daemon support multi-link ppp?

Thanks,
Bernie

badnu1s
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Re: long-range wireless board

Tue Oct 07, 2014 3:15 pm

P.S. Multi-link point to point would be another reason for going with the development kits over the rpi900 so that all interfaces are available locally.

mholling
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Re: long-range wireless board

Wed Oct 08, 2014 12:49 am

My impression of the DNT900 is that they're not really intended for streaming or other, high-bandwidth uses. They're more of a general telemetry device, with range and robust performance in a noisy RF environment being their strong points. That having been said, I have managed to stream video over these radios, albeit at fairly low bitrate. For higher bandwidth applications at closer proximity, definitely a WiFi solution would be a strong candidate, and the linux support of course will be excellent.

Your idea to use the radio's EX_SYNC input signal to aggregate multiple radio links is an interesting one. Way past my level of expertise so I've no idea how effective it would be! And you would need to build some circuitry to generate the pulse train. Regarding multi-link PPP: my driver (technically a line discipline) talks to the local radio in protocol mode, determines what remote radios are connected, and presents a virtual TTY (/dev/ttyDNT*) for each remote radio. So if you had multiple radio links between the same base and remotes, you'd have multiple TTYs, just as if you had multiple wired serial connections. The pppd manpage does suggest that it supports multilink PPP, so I see no reason why it wouldn't work. That's in theory of course; I've not tried it myself!
RPi900 - long-range wireless for Raspberry Pi.

funfrancis
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Re: long-range wireless board

Tue Oct 20, 2015 2:48 am

is it possible to use it with the Raspberry pi 2

mholling
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Re: long-range wireless board

Sat Oct 24, 2015 10:51 am

funfrancis wrote:is it possible to use it with the Raspberry pi 2
Unfortunately not, due to the changed GPIO header in the newer models. An original model B is needed. (Still available from RS, last I checked.)
RPi900 - long-range wireless for Raspberry Pi.

funfrancis
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Re: long-range wireless board

Thu Oct 29, 2015 10:01 am

mholling wrote:
funfrancis wrote:is it possible to use it with the Raspberry pi 2
Unfortunately not, due to the changed GPIO header in the newer models. An original model B is needed. (Still available from RS, last I checked.)
Thanks

Is there any other telemetry that i can use with the Raspberry Pi 2 so that I can communicate with the Pi from a remote location.

mholling
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Re: long-range wireless board

Sat Jul 23, 2016 10:07 am

Just bumping this age-old post for a status update. The RPi900 board became troublesome to use when the newer models (2, 3, Zero) were introduced, due to the expanded GPIO header. Financial constraints prevented me from updating the RPi900 board to accommodate the change.

A small modification was figured out which allows RPi900 boards to be used with the newer Raspberry Pi models. A couple of jumper wires are all that's needed. Software setup remains unchanged. Instructions for this mod are on the RPi900 site:

http://rpi900.com/tutorials/40-pin-head ... ation.html
http://rpi900.com/tutorials/pi-zero-modification.html

The Pi Zero is a particularly good fit for this modification. (Seems like they're widely available at last!) They give a pretty compact setup for a remote station.

Image
RPi900 - long-range wireless for Raspberry Pi.

Ibizibbik
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Re: long-range wireless board

Sun Nov 06, 2016 8:17 pm

You say that the whole radio set only costs $70, but 2 boards is $70 and then you also have to buy 2 radio chips which are over $80 a piece. Or am i confused?

Please help me on this, i was really looking forward to using this but if its much more than 70 its out of my budget.
Just because you know very little does not mean you are stupid.

mholling
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Re: long-range wireless board

Sun Nov 06, 2016 10:11 pm

Yes you're correct, the RPi900 boards are $70 per pair, and the radios are $80-$90 each from DigiKey or the like.

An RPi900 project is unlikely to be particularly cheap, especially once you factor in other costs (external antennas, enclosures, solar panels and controllers, batteries etc.) Having said that, the DNT900 was the best value 900 MHz radio going at the time of my design, and is still pretty competitive I expect.
RPi900 - long-range wireless for Raspberry Pi.

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