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We're making an open-source $30 GPS/mesh radio, would like advice

meshtastic.org

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Re: We're making an open-source $30 GPS/mesh radio, would like advice

#41

Post by punkgeek »

alexisread wrote: post #18

Not an expert by any means, but I'd suggest looking at the Dash7 protocol/ firmware as a reference for the mesh, security and positioning. It's been around a while and seems robust. Open source, royalty free, low power, high range (several km even in urban areas), medium bandwidth, runs on several lora boards. https://dash7-alliance.org/

ooh. That is great advice! We used the RadioHead mesh solution but it is super non optimal for us and we plan to switch. I'll definitely do some reading on DASH7.

Re: We're making an open-source $30 GPS/mesh radio, would like advice

#43

Post by madengr »

generatorguy wrote: post #31
superkuh wrote: post #22

Earlier quoted context omitted.

You're wrong. It's a mistake to treat terrain and foliage as the same thing. I have extensive experience with 3 completely different, narrowband and wideband, 902-928 MHz radio data systems as well as just playing around in the range with my software defined radios (hackrf, rtlsdr, etc). 902-928 has almost no advantage over 2.4 GHz when it comes to line of sight issues with terrain. In fact, it's more problematic due…

It sounds like you agree 900 MHz will be much better than 2.4 GHz in this non line of sight application so long as the obstructions are trees and foliage and not terrain. I would expect to be able to send a few bytes between two stations maybe 400m apart through non-line of sight forest with 900 MHz and both stations at the same elevation. Certainly the grandparent quoting miles would be for mountain top to mountain…

This is all assuming they use antennas that are optimized for the application. If they use a “chip” antenna, performance will suck.

Re: We're making an open-source $30 GPS/mesh radio, would like advice

#46

Post by jki275 »

superkuh wrote: post #22
generatorguy wrote: post #21

Earlier quoted context omitted.

915 MHz goes a lot farther than 2.4 GHz. At very low bit rates you need very little SNR. There is probably very low noise out in hiking environments. Yes, attenuation due to terrain is going to be a killer, but my experience with non line of sight 900 MHz links blasting through trees leads me to believe it would be workable for low bit rate data between a series of hikers along the same trail. It is sending only loca…

You're wrong. It's a mistake to treat terrain and foliage as the same thing. I have extensive experience with 3 completely different, narrowband and wideband, 902-928 MHz radio data systems as well as just playing around in the range with my software defined radios (hackrf, rtlsdr, etc). 902-928 has almost no advantage over 2.4 GHz when it comes to line of sight issues with terrain. In fact, it's more problematic due…

Not sure why this was downvoted, it's exactly correct.

Re: We're making an open-source $30 GPS/mesh radio, would like advice

#47

Post by punkgeek »

bigiain wrote: post #40
ourlordcaffeine wrote: post #12

I guess my only advice is make sure the software keeps to the duty cycle limits of the license free band. And note that different countries may have different regulations on what is allowed on the frequency LoRa uses, if using it is even allowed.

Also which of the ISM bands are valid in which country. (We sold off the bottom half the 915 band here to telcos, so only the upper half of it is available in .au)

ooh. good to know. here's what we are doing now for the regions we know. Someone is sending in a PR soon for the extra 440ish band in EU soon.

https://github.com/meshtastic/Meshtastic-esp32/blob/master/s...

Re: We're making an open-source $30 GPS/mesh radio, would like advice

#48

Post by WrtCdEvrydy »

punkgeek wrote: post #2

Hi ya'll, so we've spent a few weeks making device software and an android app to convert a $30 chinese gps/radio into a long range mesh radio for hikers. It is working fairly well now (though still an alpha) and we'd love more people to try it and/or have fun coding on it. We got about 30 users (and some devs from this hackaday article) but we'd love more users and devs to join this happy-happy project: https://hack…

This is so cool... I spent six months doing research on a routing layer for mesh Android devices (using Bluetooth and Wifi). This would probably make a lot of what I originally tried out a lot easier.

Edit: The issue was making a jump from a local cluster to another cluster far away as local messaging was easy but the further out, the harder it became to maintain connectivity since the amount of devices entering and leaving a mesh became a factor. We actually thought of using amateur radio (to basically allow you to extend the range using them for transfer)

Re: We're making an open-source $30 GPS/mesh radio, would like advice

#49

Post by generatorguy »

madengr wrote: post #43
generatorguy wrote: post #31

Earlier quoted context omitted.

It sounds like you agree 900 MHz will be much better than 2.4 GHz in this non line of sight application so long as the obstructions are trees and foliage and not terrain. I would expect to be able to send a few bytes between two stations maybe 400m apart through non-line of sight forest with 900 MHz and both stations at the same elevation. Certainly the grandparent quoting miles would be for mountain top to mountain…

This is all assuming they use antennas that are optimized for the application. If they use a “chip” antenna, performance will suck.

the video on their web page shows an external antenna, looks like a dipole.

Re: We're making an open-source $30 GPS/mesh radio, would like advice

#50

Post by rapjr9 »

Note that there are limits to how large a mesh network can scale, it's likely to start running into problems with several hundred users. You can scale larger by limiting data to short text messages, but you'll probably never be able to handle more than 10,000 users, unless you can find a way to create high bandwidth backbone links between clusters of users. There has been a lot of research on this in the wireless sensor network research community and in the WiFi mesh network research community also. A concert going crowd could easily cause a mesh network to become un-useably slow if everyone was trying to use it at the same time.
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