Meet FIREFLY: Lightweight, Improvised Portable Relay Nodes (EASY!)


Sometimes you just need a node.

It could be for testing coverage and signal strength at a location.
It could be an weekend event outside your usual mesh network or in a remoate area.
It could be an emergency situation, with regular communications down.

The small size of the goTenna Mesh and its handy straps make it easy to deploy it to serve all those needs and more. Slinging it up in a tree or leaving it exposed on a high point will work – it’s somewhat resistant to moisture. But for better results with all but the briefest of uses, some protection from the elements seems a prerequisite.

I’ve been building stationary relay nodes out of Pelican-clone boxes. These are very portable, but not exactly something most of us would stash away for emergency use in our pack. They could be pulled up into a tree, but they are heavy and somewhat out of balance for suspending in trees with their ungainly solar panels, etc.

I tend to save stuff, as you never know what it will come on handy on a project. This one popped into my head earlier this evening, but others may have similar example of lightweight, improvised, or emergency rigging to help a relay node work better under less than ideal conditions away from home. I’ll bet there are a lot of such ideas in Puerto Rico, for instance. Feel free to add your thoughts or creations.

This is what I call a Firefly.

It’s a 23.5 oz plastic jar for tropical fruit salad by a well-known company, but similar containers are widely available. Just don’t use glass.

You’ll also need a 62" bootlace or similar light cord; a 6" ty-wrap; an extra container lid; and a goTenna Mesh in Relay Mode. A battery pack like a Voltaic V-15 will extend the node life between chargings. You could even sling a solar panel underneath, if you create a way to avoid it spinning on its line.

Drill quarter-inch holes in the lid and bottom of the jar. Fold the bootlace in two, and thread the folded end through the lid and hole in bottom of the jar. Knot the cord on both sides of the jar lid, then tie a loop to accommodate the goTenna strap in one bootlace freeend. Finally, thread the ty-wrap up through the hole, then route it back down through a slender slot punched in the plastic slot of the lid. It should look something like this.

With the Ty-wrap partially threaded through the lid.

Don’t cut the loose ends of the Ty-wrap or bootlace. You need them to assist in pulling the lid back down and out of the jar when servicing it. It should luck something like this when unshucked from the jar.

Then you pull the cord up to seat the lid inside the bottom of the jar. If all you need is a day’s worth of coverage, then the goTenna Mesh unit has you covered.

Need more? the Voltaic V1 battery pack will just slip inside the jar’s mouth if you pucker it up a bit. You can use bigger jars here, but I think this is about the smallest jar that can accommodate bother the radio and goTea Mesh

Things are pretty packed inside, but everything fits well.

With the extra batteries aboard, it’s a good thing to take the extra jar cap and thread it on to keep everything in the jar.

A knot can be tied near the top of the bootlace loop to keep from having to restring the guts of the Firefly every time you take it apart.

The semi-clear plastic housing is tough, RF-transparent, and lets you cut it as needed. You can observe the operating info LEDs from the ground, depending on how far up you get it. It’s small and portable. All you need is a long rope and you can quickly get the relay high up, as can several other methods. The whole package weighs more the the goTenna, so helps with penetrating the tree branches and getting it back down through them. The Firefly is priced right, rugged and will serve your needs for protecting a relay “on the fly.”


I love this because what you’ve done is simple enough for people who don’t know their way around a soldering iron (read: most people — like me!) to pull this together. Amazing work!! I love the name too. :slight_smile:

(I updated your thread title slightly so that more people find/click on it!)


Thanks for the kind words, Daniela. I like simple and easy, but also find that such projects build confidence for taking on more challenging work.

The illustration is wonderful. When I saw the goTenna’s LED glowing in the jar, I know what I had was a Firefly:boom:

The re-title is great, too! I have a few more simple hacks up my sleeve that I’ll add as the percolate into something useful, get pics taken and feel in the mood to write. I encourage everyone to share, as it makes the mesh stronger.:muscle:


I have been using a Mayo container and tape attached to PVC. The PVC is just to keep it away from the collapsible metal flagpole. Other nearby metal can detune the antenna. The flagpole is from Harbor freight and it’s great for testing or mobile use. If you expect any temperature swings put a desiccant inside with the Gotenna to prevent condensation building up. Rice or cat litter works just fine for that purpose.


The HF flagpole is a great idea. Its 20’ height would actually place it about where I need it at about the height all 3 of my nodes currently are at. Around here we do have plenty of trees to loft lines into to pull a Firefly or other contraption up clear many obstructions, but there are place out West that could use this very much.

What do you use as a base or to otherwise hold it up?

Speaking of lofting lines, is there anything other than a slingshot and fishing weights (I’ve used this method for years to set-up temp shortwave antennas when camping) to get a light line over a tree that could be recommended? I’m thinking maybe a very light weight crossbow that is basically toy grade, but able to function well enough to get a line up.


I have a a PVC pipe attached to my fence that I can quickly slide the pole into. To set something like that up elsewhere a stake in the ground holds the base and guy wires attached to stakes give it stability. There are really neat telescoping masts made for this purpose that go as high as 60 feet.

Many amateur radio operaters use potato guns that shoot tennis balls to hang lines. I personally use the slingshot method.


Here I could see welding a round tube for a receiver socket on the front or rear bumper of the truck (or onto a receiver tube for a trailer hitch.)

The potato gun would work well, but not very stealthy. The slingshot may be the best solution overall speed; easy to deploy, accurate, cheap…


I welded a tube to the bumper of the Westfalia that we dropped our “tower” into.
As they say, “Necessity is a mother”.


Not everyone says it that way but I get it.


@bbwr10coqsm Do you anticipate much weather infiltrating through the hole on “top” (as it hangs)? Could you prevent that by attaching the hang-me-in-a-tree cord only to the exterior (by glue or tape or a loop/knot around some projection on the jar, etc.), and then use a separate cord attached to the interior of the jar lid that attaches to the innards, making it easier to pull them out and stuff them back in. That might leave the jar’s weather-proof-ness in tact.

Another thought… Would it be possible/practical to attach one of those roll up solar panels to the outside of the jar, feed it’s input through some weather-sealed penetration of the jar, add whatever small electronics necessary, if any, and make the unit more independent? I have not played with the roll up panels, and I have not been very successful assembling anything that requires wires and batteries (no, really!), and so I don’t really know the practicality of that…

Just wondering outloud…


The outside surface of a 1L jar would not be enough collection area to charge the device, even if it were all facing the sun.


I did anticipate this, but left my solution out of the original presuming this starts off as a quick and dirty hack. I’m not too worried about water, since the goTenna package is fairly well sealed (once you’ve taken one apart that’s somewhat more obvious although it’s not waterproof.)

However, I’d not want to seal the hole up in the jar’s bottom (the top of the Firefly), as it provides the ability to slide the jar up and down the line for access.

Where you’d want to apply a dab of silicone or other sealant would be to the knot that’s tied on the top side of the inner green jar lid. Moisture may still enter, but the lid acts like a tiny umbrella and deflects it downward if it enters. Then you need to leave a way out for the water by either leaving the second cap off the bottom of the Firefly or by placing a couple of strategically placed drain holes in that second (bottom) cap.

As for solar, maybe. I designed the Firefly to provide a means more for a temporary node than something that would need more than a single battery pack’s power… The biggest problem with solar for the Firefly is that it’s designed to be suspended by a single line, making it susceptible to spinning or otherwise rotating on the line

There are solutions to this, but all involve more trouble. A “tag line” could be attached to the bottom of the Firefly, then tied off to keep it from spinning. Trickier yet would be a separate solar panel that could be located where best oriented to pick up the rays. The power cord between the panel and Firefly would keep it from rotating. Finally a triangular arrangement of panels dangling below the node could provide enough power .


@dennilee and @bbwr10coqsm Has anyone figured out how little solar power would be necessary to keep a smallish (yeah, depends on what “smallish” means) external battery sufficiently charged to recharge the GTM battery? You are certainly right about the jar being a very small surface, plus the spinning factor, plus us likely hanging this in a tree, and so on. :upside_down_face:

So, for an example, the Goal Zero Flip 20 recharger is an 18.7Wh 5200mAh battery. The GZ site says that it takes a 7W panel about 5 hours to recharge the battery, in ideal conditions. If you tuck one of those batteries in as the longer-life battery to keep the GTM charged, how little solar power do you think you might need to keep the GZ battery charged up ahead of the GTM recharging load? Any guesses (I have not played with solar stuff enough to know how to guesstimate this)? A 7W panel would be pretty huge to hang on a small plastic jar.

While there are a number of water bottles out there with built-in tiny panels to run some LEDs, I would guess (yes, uneducated) that these would not be powerful enough to keep much of anything charged up enough. And, they’d take someone smart in HW mods, like you and some of the others here, to hack them for the purpose.

Again, more wondering out loud… just wondering how to make some of these way cool ideas you all are dreaming up a little more maintenance free or whatever. :wink:


Think I’ve seen some numbers around 250 mah/day seems to stick in my mind, but that does sound a little low.

As for the rated recharge numbers of solar panels, that’s done under ideal conditions, i.e. it’s assumed temps are optimal (it’s been cold here and that affects batteries a lot), full sun, and the panel pointed favorably toward it. I mentioned I’m starting to suspect for field use doubling or possibly tripling that number might be needed to ensure reliable operation.

Thus my suggestion to use a triple set of panels triangularly configured so that even if they rotate and with the sun moving there would at least one panel’s worth exposed to good sun every day. Ideally, they should all be rated well above the GTMs recharge demands. I guess you could say what I’m doing now is trying to see what I can get away with. My guess would be to use a minimum of 3 x 3.5 W panels for this “dangling triangle” configuration , but I haven’t verified yet that a single 3.5 W panel, well-located and stationary, will be sufficient based on my winter-time experience so far.


@henry_sheard My rule of thumb for reality checking PV claims is 1000w/m^2. The total solar flux (all wavelengths) measured by satellites is about 1.4 kW/m². So down here 1Kw/m^2 is probably an optimistic best case scenario. And that is square on in full sun.
You spoke of a 7w PV. If that is 5vdc them its ideal output is 1.4A.


@dennilee and @bbwr10coqsm Thanks for all that info!! I’ll wander off for a bit and ponder it all… :sunglasses:


@bbwr10coqsm very well done, sir/ma’am!


I don’t know where these numbers came from but here is a good quote.


In some cases, you may want to consider a higher battery pack minimum mAh. I’ve been using 4000 mAh pcaks and they just aren’t enough for the short days and cloud cover of the wintery Midwest. It might be better if I was using a larger solar panel, as 2 W is clearly not large enough and 3.5 W seems marginal in the portable nodes I’ve used so far.

On the other hand, for a temp node, it depends on how long temporary is if unsupplemented by solar. For a long weekend, 2000 mAh should be sufficient assuming starting with a fully charged goTenna Mesh.


Ok, so I had this goTenna Mesh that needed a new case. It had been run down by a Land Cruiser, yet it somehow survived after an emergency caseodectomy that left it unprotected and liable to do strange things with its LEDs if bumped. Plus when I was wandering through the big box today trying to forget the morning extraction with a little distractive consumption I came across these, which at first I wasn’t sure were deep enough inside to suit what I did next. Turns out there was plenty of room if it’s only your goTenna going in the case.

And the SuperFly was born. It’s a bit upscale, but still accessible at reasonable prices on the street. I paid $8 each for these, scarfing up the last clear one for, well, obvious reasons - to stuff a big ol’ battery pack in with its own 1.5 W solar cell. This one is labeled at being 20,000 mAh but was sold as 8,000 mAh (a more reasonable number I believe). It looks like it’s going to be a tight fit.

This is a rather hard and somwhat brittle plastic. I drilled very slowly, opening up the hole with bigger and bigger bits, then slotting the hole with a jeweler’s saw. You need to line the hole up with the resting position of the pack inside the case once you’ve used a file to adjust the lip of the case that provides a seal. Don’t worry, I’ve got a plan to seal it. But you have to file the lip of the other half to fit this pack in. Maybe yours will be smaller? Or bigger? You’ll probably need a bigger case then.

Here’s a couple of views of the USB exit.

In the upper case, the fit isn’t tight, the hole only need pass the cable through and doesn’t really need sealed in most cases as it points down.

You can use a shiny new goTenna Mesh, but all I had as this beat up ol’ thing…

Then you string it up. The bracket at the bottom allows you to attach tag lines to hold the position or rotate the solar cell.

It probably won’t keep up permanently at this poor sun angle, but supplements several days of power in the battery back. How long? I’ll be hanging it outside or in a sunny window for a test and will advise how it does. The battery pack has an always on feature, so as long as this test node has juice, it’ll be meshed.