High School Robotics Course using the Particle.io Mesh Devices Blog


#81

Not sure, that would be something to try out, but I’d expect that this should lock the gateway flag, otherwise this would be an easy way to mimik a micro network which could otherwise easily be converted into a HA mesh.


#82

2 Problems. First using the featherwing does not guarantee it is a gateway. This bit of code at the top of your program

STARTUP(System.enableFeature(FEATURE_ETHERNET_DETECTION));

makes the featherwing plug and play, gives the Xenon internet but does not on it’s own setup a gateway.

If you use the App to make a gateway using the Feathering and a xenon, you still have the problem of not being able to join to any other mesh network. So by taking the featherwing off of your xenon it becomes useless because it can’t be part of any other network except the network that is was setup to be a part of.

Hopefully at some point Particle is going to allow us to join multiple gateways to a mesh network…


#83

So I went out to test if glass hurt the RF signal. Xenon and Argon in jam jars. When I got to the location I wanted to set a base line and didn’t want to walk too far so I used a Xenon and Argon without Mesh Antenna. Should get about 300 m.

But today Thinking about Antennas tend to be about 1/4 the wavelength. I did some math. Velocity = Wavelength x frequency.

or Wavelength = Velocity (Light) /Fequency = 3.00e+8 m/s / 2.4 1e+9 1/s = 0.125 m about 13 cm or 5 inches So the perfect antenna should be about 3 cm or about an inch.

Looking at the Mesh/Wifi antennas they have a wire but the antenna part is about an inch, well so is the Argon and Xenon about an inch long. So to get my base line I set them up both vertically and started walking. HOLLY SMOKE at 600 m I came to a slight curve, so I never did find the full distance.

MOUNT YOUR MESH DEVICES VERTICALLY to get the most of the internal antenna!

I finally had to position the devices for the worst range to just be able to test the glass, which seemed to have no effect on the distance.

I think this is worth it’s own topic.


Mount the Mesh Devices Vertically
#84

Spurred on by the above discovery I spent the afternoon researching how to make a parabolic reflector.

but they both seemed like a lot of work

I did design a parabolic shape to 3D Print tomorrow, but then I would have to cover it with some kind of metal paint.

so I dug a bit deeper and found this image

image

which reminded me that radio waves can be reflected by a metal mesh (Some website mentioned the mesh should be at least 1/10 the wavelength) for 2.4 GHz the mesh would be like the mesh in a microwave.

So I found a Summer Salad insect protector. Was super excited to try it out, but it did not seem to help at all :disappointed:.


#85

You might be oversimplifying a directional antenna a bit. But, the metal mesh doesn’t do a anything by itself. Rather, the metal mesh is supposed to create an artificial ground plane. Try attaching the metal mesh to ground. It might work…

The shape of the parabola doesn’t look right either.


#86

Nice… also I was not testing line of sight, so I will do that when I get a chance. So just a wire that attaches to the ground would be enough. I might just place the thing on the ground. Finding the correct focal point might take a bit of testing,

Those companies that make salad protectors should really concentrate more on making correct parabola shapes.


#87

So today my thinking was: Since a metallic mesh stops or reflects RF signals, what about the breadboard the Mesh Devices are attached to. If you take apart a breadboard it is a mesh of wires (however they are not interconnected). If I hang a mesh device vertically but reverse the direction so the breadboard is facing my Xenon. I should get a very reduced max distance.

Made no difference. Got the same max distance.


#88

perhaps using an external yagi antenna would work as well with the mesh transmissions as it has with wifi transmissions.


#89

Look into 2.4 Ghz patch antennas and how they are designed. I think you can build some yourself for testing. It looks like there is a grounded sheet behind the actual receiving antenna.

They work really well on the DJI drone and gave me tons more range. I know the DJI radios were running at 5.8 & 2.4 GHz.


#90

Wow. Very interesting. Best link I found was this. Might be a good student project.

Be nice to 3D Print the base of the Yagi antenna and just push the correctly cut paper clips into the correct locations. I will check thingiverse.com to see if someone has already done it.

That print seems very complex. I might just make my own simple one.

My other idea today was to convert a cooking Wok into a parabolic antenna. Found some links on that


#91

I’m no expert, but this is just a reminder about directional antennas:
Any gain in 1 direction is lost for other directions.

Take a look at the radiation patterns for various types of RF antennas.

A Yagi is a wonderful device and has a few uses in a Mesh Network.
If you’re only looking at Point-to-Point, then a Yagi will perform the best.

But in “general” a Mesh network will operate better with omnidirectional antennas.
The key is coverage area, with overlap & redundancy.

Patch antennas can provide benefit along the borders of the Mesh Footprint.

Another aspect is your sensor nodes (which will normally be Omni’s). It doesn’t do much good to have a High Gain Antenna at a Router that can receive RF from a node, if the node (much less gain) isn’t able to communicate back to the Router.

This isn’t meant to try and discourage you in any way. There are plenty of cases where a few Xenons would benefit from High Gain Antennas to communicate with their gateway, just not in a traditional “Mesh Network” sense.


#92

What is the concept of a patch antenna? Looks like a capacitor. 2 metal circular sheets of a certain size separated by a gap.

Found this nice calculator for a patch antenna
https://www.everythingrf.com/rf-calculators/microstrip-patch-antenna-calculator

Now I need to know the dielectric constant for PLA.
This site has too much information https://www.hindawi.com/journals/amse/2017/6913835/

By the way I can 3D print electrically conductive material. Is a patch antenna something I could 3D print? I made touch capacitive sensors for the photon last year.

This site has a wealth of DIY Antenna information

http://www.wlan.org.uk/diy-ant.html


#93

I agree with this and @peekay123 would suggest just putting another repeater between your gateway and end-point, however knowing how well or badly external antenna work with the mesh could really help some business’s where a few strategically placed antenna really stabilizes their mesh.

An example that comes to mind would be a farm with some gaps between the fields.


#94

A few students put together my one piece, 16 inch, 3D printed Yagi antenna. Just have to figure out how to connect it

Note: My school 3D printer has a 12 x 12 x 12 inch print area, so diagonally this print just fit. (actually hung off the end by 2 mm)

Using the diagram below that shows the lengths of the paper clips and the length from the start all in mm. The 3D printing program I uses (blender.org) defaults to mm and I can put the image into the background and resize it to the exact measurement.

The green line is the split loop paperclip that gets both ground and Antenna connection from the device.


#95

Last day of school so I thought I would 3D print a test Patch Antenna. Surprised how big it was. The red represnts electrically conductive material and the green would be regular PLA 3D Print material.

This design has a hole running the length of the red beam and also the ground so that a wire could be placed fully through it to connect an array of patch antennas as in the diagram.

Theoretically you could setup an array like this

Just found this web page about patch antenna width compared to length.


#96

Pretty cool. Bet you could make some decent antennas this way.


#97

Interesting observations. (And a clever use of the jars, so you could see the LEDs!) I’m a Ham Radio operator, and what you say makes sense (for a quarter-wave antenna counerpoised to “signal ground”). You mention mounting them all vertically… but the key is really to mount them parallel to each other. (So, if you mount them all horizontally, and all are pointing North, you’d see a similar signal strength.) Essentially, your signal is radiating directly away from the antenna element, an the strongest signal is perpendicular to the antenna element… I’ll post a bit more aboutt this in the separate thread.

I finally have my four Xenons up, on RC.27, and ready to code… but when I flashed blink-an-led with the Web IDE, my Xenon lost it’s network connection, so I’m not out of the woods yet. I am ready to start rereading the earlier posts in this thread. :slight_smile:


#98

For that green salad bowl: Try poking toothpicks through the mesh at various points. Make them perpendicular to the mesh at each point. Then look to see if they are all pointing to the same “focal point”. I thinkthe FP for that green bowl looks about 1" above the rim… For a parabola, that would make a huge performance difference.

Check with your local hardware store, and see if they have a small pot of Rustoleum aluminum silver paint… (if you don’t plan to use that bowl for salad ever again. :wink:

Regarding Yagi antennas… you get more directivity (focus) for your signal in the direction of the beam away from the “driven” element (the folded paperclip). The more elements you have, the more focus you get, but then you have to make sure the antennas are pointed very well… Consider making a couple shorter versions for testing, which will be more forgiving about aiming. :slight_smile:


#99

What a great idea for a student project. Give them some mesh and have them make their own parabolic reflector with toothpick proof of the Focal Point.

Thanks @zonker for all the likes. Biggest challenge coming up:

I have bought several (on back order) OpenThread USB dongles and now need to get them going with the Border Router and hook them up to the Particle Mesh devices. Probably a big waste of money as the mesh devices will not play nicely but needs to be attempted. Be really nice, but not likely, if Particle released an OpenThread version of their Mesh firmware.

Just found this quote I read a while back but could not find the link:

The Thread devices in this Codelab are a specific kind of Full Thread Device (FTD) called a Router Eligible End Device (REED). This means they can function as either a Router or End Device, and can promote themselves from an End Device to a Router. (I think this would be equivalent to an Argon Gateway)

Thread can support up to 32 Routers, but tries to keep the number of Routers between 16 and 23. If a REED attaches as an End Device (child) and the number of Routers is below 16, after a random time period within two minutes it automatically promotes itself to a Router.

https://codelabs.developers.google.com/codelabs/openthread-hardware/#9

I think this means if you have more than 23 Argons in a thread, any more Argons will probably downgrade from gateways to the equivalent of a Xenon as endpoints, unless for some reason the network senses it needs more Argon gateways.


#100

Couple of things happening:

@Zonker has a nice summary page of his Particle process at http://arduinoprojectz.pbworks.com/w/page/131058369/Particle%20Mesh%20Dashboard

My Fanstel USB Thread Dongles arrived, still need to wait for the Nordic and Seeedstudio ones

On ubuntu I can see these dongles using

ls /dev/ttyA*

but can’t seem to move the NCP image to the dongle.

If I load the dongle on my windows machine it auto enters DFU mode, but I am not sure which software to use with it. Bit worried that the Dongle has no buttons to push so not sure how to get it back to DFU mode if I install anything on it.

Nordic has some fancy software and Apps that might work with it. The nrftoolbox for android

and and outdatedSDK for windows

Looks like Nordic is moving away from OpenThread.

Lots to learn as I dig a bit deeper.

Found this interesting bit of information about how to eventually use some of the OpenThread C++ commands with Particle Mesh devices but have a fair bit to learn about how to do it. Once again a bit confused about how to move programs from the computer to the devices.

Wondering if anyone has messed around with cloud virtual linux boxes such as: https://repl.it or https://glitch.com for working on either the Particle/firmware github or the Openthread github . I teach using http://c9.io but it needs a creditcard to get started. (It costs $1 per month to assign all my students to have logins to a ubuntu virtual machine. Not sure if it has fully been absorbed by AWS, but the community does not seem very active lately.)

These virtual machines might work with an Over The Air type Mesh device installation but will not work with anything that needs physical connections, however often fun just to see how an installation works using the virtual box before trying it on your own ubuntu computer.

Most of the information about the OpenThread Border Router will be at this thread, but I will probably post summaries here.


Using Particle Mesh Devices with the OpenThread Border Router