A while ago I organised a group buy of Anthony F4GOH's Arduino Nano/DRA818 APRS Tracker modules, along with all the necessary components - most of which were shipped from China. Dealing with all of that is a story for another day, suffice to say that ordering on the leading edge of a global pandemic originating in China was probably not my best move...

I have kept three of the modules for myself, and due to an ordering snafu I've ended up with an additional one, although I don't have all of the components to populate it at the moment.

The module neatly brings together both the Arduino Nano, as the brains of the device and a DRA818 module (which can be either the VHF or UHF version, I've stuck with VHF) and optionally the following:

• A GPS module
• An OLED screen (on the I2C bus, so this could be any I2C screen or indeed any other I2C modules could also be connected to the bus).
• An SD Card module.

Additionally there is a 6-pin header which provides Vcc, GND and access to the Arduino's pins A0-3. Pin A3 is particularly interesting as this is the receive audio from the DRA818 module.

Anthony provides Arduino sketches to use the module as both an APRS tracker and a simple APRS Digipeater, which is actually more like a dumb APRS repeater - it doesn't do anything like modifying the APRS path which a 'proper' digipeater should do. In this mode the module also emulates a TinyTrak4 TNC, so software like SARTrack or PinPoint APRS can run on a PC attached to the Arduino's USB port to give a graphical view of nearby APRS stations. I assume this will also work with Xastir on Linux although I haven't tried that yet. Use in this way could also turn the system into an iGate. I don't know if it will run as a TX iGate or not.

Fitting a full AX25 stack into an Arduino Nano is pretty impressive - there's no way I could have done that so well done to Anthony and the various others who came up with parts of it, including Robert, KI4MCW who coded the AX25 decoding routines. The provided sketches only really scrape the surface of what's possible with these modules. I intend to build on the fantastic pre-existing work to create additional sketches for these devices. The following are either in progress or planned:

• Add SmartBeacon to the tracker (Done!)
• Add some sort of 'location blacklist' to prevent beaconing from certain locations (maybe you don't want to beacon from home, or when you're refuelling your car etc.) (Done!)
• Adding proper path-handling to the existing digipeater mode.
• Sketch to act as 'personal digipeater' (i.e. only digipeating packets originating from one of my own tracker modules).
• Sketch to act as an APRS pager to display APRS messages sent to me. Hopefully this can be built in to the tracker sketch.
• Sketch to act as an iGate. This would need some form of network connectivity - probably an ESP8266 module attached to a SoftwareSerial port on the expansion header. This could be an expansion to the TNC/Digipeater sketch.
• Add Bluetooth Serial to the module. This should be possible by either adding an HC-05 module or possibly using an Arduino Nano 33 IoT device, although these are 3.3V, not 5V which might mean that changes to the board are needed. Changing to a board with a different clock speed will probably mean that some of the constants in TNC.c and DRAPRS.c need recalculating (specifically refclk).

Some none-APRS ideas:

• 2m ARDF ('foxhunt') beacon, with control via DTMF. Thinking about it, control could even be over Packet/APRS messages!
• Automated OSCAR station - Arduino can calculate which satellites are in view and automatically tune to one (correcting for doppler). Satellite Az/El can be displayed on the screen for antenna pointing. A software serial port could be added to the extension port to control a rotator too, you could even add an electronic compass to the module to help with antenna pointing. This could be used to just listen to the satellite audio, or (subject to programming space on the Arduino) with the APRS routines to send/receive APRS packets to suitable satellites. It may be possible to use two of these modules together, one on 2m and the other on 70cm for a duplex satellite solution too (although see note about filtering).

Problems

The only issue with the module that I've identified so far is that there is no filtering on the RF output. The DRA818 modules are known to not have a particularly clean output so some sort of output filter should really be added. The Mini-Circuits LFCN-16+ filter seems to fit the bill nicely.