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

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

#21

Post by generatorguy »

superkuh wrote: post #11
jkoberg wrote: post #8

Earlier quoted context omitted.

What frequency band are you using? ISM is the only one that permits store-and-forward / automatic operation, as the gotenna people found. You say a few miles per node - I am having trouble seeing how that's possible without elevating all the nodes

He's gotta be assuming the nodes have clear line of sight and fresnel zone. The maximum distance for the link budget in a perfect situation. In practice it probably cuts off at the nearest rise in the ground or depression. But they're still cool and I still want some for non-hiking applications. With the very low power idle and low cost they could be set up with solar panels in the tops of trees or in similar high he…

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 location and text messages so intermittent link status or re-tries due to temporarily terrain/foliage obstructions will not cause degradation in service that you would experience trying to watch netflix over this mesh.

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

#22

Post by superkuh »

generatorguy wrote: post #21
superkuh wrote: post #11

Earlier quoted context omitted.

He's gotta be assuming the nodes have clear line of sight and fresnel zone. The maximum distance for the link budget in a perfect situation. In practice it probably cuts off at the nearest rise in the ground or depression. But they're still cool and I still want some for non-hiking applications. With the very low power idle and low cost they could be set up with solar panels in the tops of trees or in similar high he…

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 to the increased size of the fresnel zone. Sure, it does better through trees but a slight rise of ground is just as much of a problem for 915 and 2400. The freq here isn't helping much. It's the chirp and LORA modulation helping the link budget. But no line of sight is no line of sight.

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

#23

Post by atourgates »

Really cool.

Seems like an open-source mashup of something like Lynq https://lynqme.com/ - and Gotenna https://gotennamesh.com/

I've never liked Gotenna's requirement to be paired with a cellphone for tracking, so I've been watching Lynq's development for a while. But, I'd much rather have an open-source solution than one that depends on the fortunes and whims of a single compnay. Particularly if there was easy-to-use commercial hardware available with the open source software.

The other downside of Lynq is that it doesn't use mesh networking, e.g., every Lynq unit can only communicate with other units it can connect to directly. That means if you have a group of 3 people all in a line, separated by 3-miles, only the person in the middle will be able to find the location of the entire group, and the people at the ends of the line would be invisible to each other.

Anyway - all that to say - I'm super-excited for your project and wish you all the best.

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

#24

Post by punkgeek »

atourgates wrote: post #23

Really cool. Seems like an open-source mashup of something like Lynq https://lynqme.com/ - and Gotenna https://gotennamesh.com/ I've never liked Gotenna's requirement to be paired with a cellphone for tracking, so I've been watching Lynq's development for a while. But, I'd much rather have an open-source solution than one that depends on the fortunes and whims of a single compnay. Particularly if there was easy-to-us…

yes, that's what we thought also. Also, the phone is optional for our case (though you need it for sending texts - if you don't have one the display still shows rxed texts and headings/distance to members of the channel)

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

#26

Post by punkgeek »

whalesalad wrote: post #14

Looks like you have already written a lot of low-level code for your device already ( https://github.com/meshtastic/Meshtastic-esp32 ) but have y'all considered taking a look at the Nerves project ( https://nerves-project.org )? You might uncover some really cool stuff in the Erlang/Elixir ecosystem for doing mesh communications.

Thanks! alas, I think that is a bit to big for what we have to work with in our ESP32s. We started our sw design based on what off the shelf hardware we could find and worked from that.

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

#28

Post by punkgeek »

zumzumzum wrote: post #15

How is it offering 'private' communications on the 33cm band? Does this band even offer good performance in hilly or mountainous terrain? These would be short range line of sight only type devices, correct? I'm still fairly new to amateur radio so I could be off. I don't see the advantage of this over something like APRS on 2M, with the exception that you don't need a license.

encryption is allowed for low duty cycle digital usage on that band.

I'm also a ham and really into APRS. But not requiring a license is a big plus, also the way these chirping radios achieve their long range with a super high noise floor so the battery life is amazing. i.e. a TTGO TBEAM will run for about eight days on (including the GPS/radio and CPU). And $30 for that board.

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

#29

Post by punkgeek »

jkoberg wrote: post #8
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…

What frequency band are you using? ISM is the only one that permits store-and-forward / automatic operation, as the gotenna people found. You say a few miles per node - I am having trouble seeing how that's possible without elevating all the nodes

Oh yes, line of sight makes a big difference (also working as mesh helps for forwarding packets). Also we use a very high spreading factor so the bit rate becomes super low (with lots of chirps)
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