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A portable rnode connected by its own wifi hotspot to a smartphone interface device

In this build of a portable Reticulum rnode, a Raspberry Pi Zero runs a RAK rnode. They are sealed in a box with a 10000 mAh battery. The Pi is running MeschChat, and MeshChat is used via the MeshChat GUI by using a browser on a smartphone (or similar device). The smartphone opens the MeshChat GUI using the Pi's IP address by using the URL <ip_address_of_pi>:8000 . The connection from the Pi to the smartphone (or other interface device) is by wifi, and that wifi is provided by the Pi itself, which runs a wifi hostpot, also known as an access point (AP). This makes the setup completely portable for use in the field. The setup details of the software are in the Pi installation instructions. As noted in those instructions, the wifi connection of the smartphone (or similar interface device) is taken up by the wifi connection to the Pi, and so the smartphone (or similar interface device) has to use a cellular data channel for any internet access. This arrangement is fine for field-testing on the move. In any case, these devices, and the mesh they seek to join, are best tested without any internet available becase that is the best simulation of a resilient communication network independent of the internet and other infrasctructure.

Why the detail? It's only a box for Pete's sake. It is quite finicky to fit all the bits firmly into a box when that box is only just the right size. The exact parts chosen can make or break the fit. So I have detailed the parts, and reasons for the choice, in case this helps to spot the possible issues when trying this build using slightly different parts. Particulary the fixing of the battery to the box via a perspex (plexiglass or acrylic) sheet, and the cable choices, are important to make it all fit tightly. I had a load of bits and bobs from other builds in the past, and managed to select from my reservoir the parts that happened to work. There is almost no way one can do this sort of task efficiently in a few hours of valuable free time, without having already acquired all the bits one could possibly need.

I used an old Samsung J3 smartphone runing Android 9 to connect to the Pi. It was found, most disappointingly, that not all phones and Anroid versions allow connection via :8000. One can of course also use a laptop. An iPhone and iPad seems to allow <ip_address_of_pi>:8000 without any problem.

The waterproof seal between the lid and the base of the box is made a long rubber seal (comes with the box) compressed around the box lid by four screws. The idea is to be able to leave the case outside, even in the rain for a short while. The case is screwed shut, but might need to be opened if the battery goes flat because: (1) there is a side button on the battery that seems to need to be pressed sometimes when the battery starts off providing power for the first time, and (2) the RAK also seems often to need to have its reset button pressed at the initial startup. This is sub-optimal at the moment, but this topic will be addressed by further work. I think being able to access the buttons without unscrewing the lid would be an optimal solution for these components, but that requires some complicated adaptions which I do not know how to make. 3D printing must be the way forwards in this regard, because arranging waterproof button presses from outside are very tricky using standard boxes.

The battery will power the Pi, and the attached RAK radio, easily for at least 24 hours. This build is intended to be re-charged once a day.

The box has a transparent lid so that one can see what status the battery has. The number is upside down when standing on its end due to the geometry of the battery outputs/inputs. The RAK has a green light that illuminates when sending, and a blue light that illuminates on receipt. If one sends a message that is shown as 'delivered' then first the green LED goes on briefly at send, or on each repeat send, and then when the delivery is confirmed, the blue light comes on briefly. I like the fact that it sits blinking in a corner.

The battery used in this build has the property that when it is plugged in to charge, or removed from charge, it cuts power to the Raspbery Pi. When I charged this device every evening over a period of many weeks, there was never a problem. The cutting of power acts as a useful tool to reset the Pi when needed. Once I experienced that the battery stopped providing power after it was plugged in briefly to reset the Pi, and so I had to open the box up to press the power button on the battery, which was a bit annoying.

Parts and build steps

1. A Raspberry Pi Zero 2W and a RAK4631 node. The two are connected, ideally, via a 5 cm short USB-C male straight to USB-C male angled connector or similar, and a 180 degree angle USB-A micro to USB-C female adaptor.

2. The Raspberry Pi Zero 2W and the RAK board are mounted above each other by 2 cm long M2 hexagonal spacers brass risers. Because the Pi and the radio board are different lengths, the two pairs of holes at one end are connected with the spacers angled.

3. VEEKTOMX Mini Power Bank 10000 mAh. The power bank (battery) can be charged at the same time as powering the Pi (pass-through charging). However the power to the Pi is briefly cut when the power bank is plugged into a charging cable. Thus far, with the software set up as stated in the Pi installation instructions, the Pi Zero starts up again each time with no problem, and in particular the wifi also re-starts. (So in fact I had initially not noticed that the Pi was restarting when plugging in the USB-C charging cable.) I will be swapping to a different battery or putting a UPS hat onto to the Pi Zero to avoid repeated unclean resets of the Pi Zero which may eventually cause a crash and failure to restart.

   The RAK radio gets its power from the Pi. The power bank has a display that tells you the percentage capacity remaining.

4. Electronic Junction Box, Waterproof IP65, Transparent Case. The transparent case lid makes the battery display and Pi and RAK lights visible. The Pi has a green LED on continuously (or intermittent when booting). The RAK has a red LED on continuously, and a green and blue intermittent LED related to transmission and reception of radio signals.
5. Drill a 6 mm (or 6.5 mm) hole for the IPEX to SMA female pigtail antenna mount. Drill the hole at a location 30 mm up from the base at one end of one side, because any lower and the battery presses against the wire coming out of the antenna mount. Fix the antenna mount using the thin bolt and washer provided in the mount set. If you have drilled a 6 mm hole, you will need to wiggle the drill a bit to make the drilled hole a litter larger, and also then the mount needs to be screwed into that hole, because the fit for a 6 mm hole is a bit too tight to put the mount in directly.
6. Use a step drill, such as a Pinava® HSS Step Drill 5-35 mm to make a hole that is only just large enough for the USB-C panel mounted socket. Warning, this particular socket does not work for both USB-C male orientations (most irritating) - rotate the USB-C cable if the battery does not indicate that it is charging. Charging ocurring is indicated on the battery display by the last digit of the percentage charged number flashing. The hole for the USB-C socket is on the same side as the antenna, so the device can stand on the long or short end. The USB-C socket's hole is located on the opposite end to the antenna, and its center is 20 mm up from the base and 28 mm away from the end. Don't mount the socket straight away, as this make putting in the battery impossible, see below. In the image below you can see the perspex sheet with six holes, placed into the base of the box (see steps 7-10).

7. The housing has six mounting points in the base, in the form of dimples with holes in the middle to accept a screw. The problem is that the screws used must be wide enough to bite into the edges of the dimples' holes to provide fixation, and yet not too short (else they won't fix anything) nor too long.
8. Use one perspex (plexiglass, acrylic) sheet. I used a 4 mm thick one, but I think a 3 mm thick one is fine. The sheet needs to be cut to fix tightly onto base of box and right up to the ends to ensure that the screw holes at not too close to the edge of the perspex, else the fix will be weak. See image in point 6 above.
9. Use two small cable-ties (dimensions 150 x 3.6 mm), daisy-chained to increase their length, to tie the battery down onto the perspex sheet. This is done twice, in two locations on the sheet. The cable-ties are preferably loosely put around the battery and perspex sheet before the sheet is screwed down.
10. Drill six, 4 mm diameter holes, to match the mounting points in the box base. This is a major fiddle, and in practice the holes need to be so precisely positioned, that in fact one has to make them a bit wider using a drill bit pushed sideways to make elongated holes to provide play. If the holes of the perspex do not match the center the holes in the dimples, so as to provide a completely free path for the screws, then it is impossible to screw the screw into the holes. So make sure the holes are good before screwing in the screws, as removing them repeatedly errodes the material of the dimples. I screwed down the perspex sheet at all six locations, but this might be overkill: though the battery is heavy and if it were loose it would likely damage the Pi and RAK radio. You may even want 6 very thin washers as well as the nuts, if you find that the screws do not quite press the perspex sheet down tightly enough (in my build the bolts, acting as spacers, rattled a litte).
11. Six, M4 x 10 mm screws from Connex Assortment Box, DP8500055 to fix the perspex sheet to base of housing. The screw bites into the plastic mounting points in the box, and this requires quite some force. Use six, M5-19 bolts (from the above set) purely as spacers between screw head and perspex, because the screws are too long.
12. Mount the USB-C socket tightly.
13. An Eightwood 868MHz antennawas selected because then the box can be used vertically or horizontally because the antenna has a hinge, and because the antenna seemed to work well in terms of reception/transmission.
14. Attach the antenna well, and before powering up the rnode. Powering up a radio without an antenna attached can cause damage to he radio because the radio's circuits cannot dissipate the power used to transmit, and the radio can overheat and fail. For good measure, the Bluetooth connection point on the RAK was provided with the Bluetooth antenna that comes with the starter pack, in order to avoid any similar damage issues should the Bluetooth be transmitting. The Bluetooth connection was not used in this build.
15. Use short cable that has an USB-A right-angle at one end and a normal USB-C end at the other to power the Pi from the USB-A port of the battery. The space is tight, so you need a plug like in the link: this where the USB-A part is the right way up to point away from the USB-C socket in the side wall, and thereby leave the USB-C power input of the battery un-obstructed. Plug the USB-C end, of the USB-A to USB-C cable from the battery, into the Pi via a right-angle USB-C female to USB-A micro male adaptor from this kit, one of which is the right way up.
16. Use a short USB-C to USB-C cable to connect the USB-C panel mount to the battery USB-C charging input. The space is very tight, but this one works.

17. The Pi and rnode, stacked as a unit, is iself tied above the power pack (battery) by a single daisy-chain of very thin cable-ties. The very thin cable-ties are tied to one of the cable-ties that hold the battery to the perspex sheet. The height of the arrangement is such that the lid, when closed, just touches the RAK radio. Mounting in this manner is sufficienlty firm so that the Pi and RAK radio do not move in the box when the box is closed.
18. The box is heated with an electric hairdryer before sealing, and a generously sized pack of silica gel desiccator is placed inside (wrapped in black cloth to make it look less ugly). In my experience when such boxes are left outside in the sun, condensation forms in the box and this is probably best avoided.
19. Write the following things on the back of the box: SSID of the wifi hotspot of the Pi, IP address of the Pi, the wifi password.
20. Reticulate on the move!

Using the rnode on the move

Using this rnode setup on the move, I was able to test both sending an image to a node 5 km away:



and receiving and image from the receipient of my image 5 km away:

Last edit 03-09-2025 MMDDYYY 12:00:00 EST