previous blog: CL REPL & QML Creator

posted 2023-12-14
updated 2024-02-16

Simple Meshtastic App

A simple app that runs on all of: Linux, macOS, Windows 10+, android 6+ (32/64 bit), iOS 12+ (including iPod touch), SailfishOS 4.5+. Tested with RAK and Heltec devices.

android: Mesh-SMS.apk  |  iOS: Mesh SMS  |  repo

TODO:
* add background mode (mobile)
* add notifications on new messages (mobile)

N.B. (android only): if you previously used a radio with the official app, you need to set the radio to 'None (disable)' in the official app first, otherwise it will not show up in this app.


Simple Meshtastic Radio

My take on a home made solution for an affordable, reliable radio:
(no superfluous parts - very low energy consumption)

Make sure both antenna and pigtail match, so they must be both SMA, or alternatively both RP-SMA.

All parts above combined cost me around 50€.

I used a soldering iron, a hot glue gun, a step drill bit, double sided tape.


Antennas

Important: never power on your radio without a mounted antenna, this can destroy your hardware (power is reflected back to the radio).

A good antenna is crucial for the radio to function properly.

A NanoVNA is very helpful to test if an antenna is resonant at the specified frequency (otherwise it's useless).
The Return Loss should be >= 10dB at the used frequency, which means that at least 90% of the power is going out of the antenna, and only 10% is reflected back to the radio.

 RL    back  out  VSWR
---------------------------
 0 dB  100%   0%  infinity
 1 dB   80%  20%  17
 2 dB   63%  37%   9
 3 dB   50%  50%   6
 5 dB   32%  68%   3.5
 6 dB   25%  75%   3
 8 dB   16%  84%   2.3
10 dB   10%  90%   2
15 dB    3%  97%   1.4
20 dB    1%  99%   1.2

RL ..... Return Loss
back ... reflected back to radio
out .... going out of antenna
VSWR ... Voltage Standing Wave Ratio

You can find good NanoVNA clones for about 50€/$ (beware of really cheap/bad clones).

The screenshot shows a very good Return Loss of 22dB.

The antenna needs to be in vertical position while testing, so it's best practice to build a little stand for it, so one can test without touching the circuit, which would inevitably falsify the measurements.

It's highly recommended to only trust specialized shops (Mouser, Rokland, RAK store) for antennas, because there is simply too much mass produced garbage out there (talking from experience).

If an antenna is totally off when I measure it, I like to dissect it.
Here you can see the inside of one good example, and the worst offenders so far (at the outside all share the exact same length of around 20cm and the exact same shape, see cut off plastic part on the left):

Here an example of a classical (home made) ground plane antenna, using an SMA socket and 2 mm copper wire, after calculating the lengths here:

Can easily be trimmed by making the vertical wire a little too long, and cutting off one mm after another until it matches perfectly, while having it attached to a NanoVNA.


Line of Sight

To easily find out if two places are within line of sight, you can use this

Path Profiler


line of sight


no line of sight


Waterproof Solar Panel Radio

The RAK store has this nice enclosure where there is enough space for both a 18650 battery and a RAK 19003 Mini Board.

The above combination is not supported by the mounting kit, so this is just a personal hack, as you can see if you zoom in on the details.