I’m far from done. Let’s start there. But… I have made a LOT of progress since I started smoking the first TNC board. Smoked a turkey in that timeframe, too – but that was intentional.
We know that BLE is sort of working – I can observe the NMEA data passed through from port B to port A across a BLE terminal on my Mac. the modules I have are not compatible with iOS. Waiting on one to be delivered still.
I decided that, while I don’t have the BLE module, this thing is SUPPOSED to be a standalone tracker, so let’s try some RF out from it.
I hacked open the end of the cable connected to the accessory port on my XPR4350, and stripped the wires I needed (had to look up which pin went where again – I lost the paper that I had originally taken notes on). solid cat 5 wires have always been a favorite for breadboards. After some jumpering, I got the radio interfaced to the TNC. It took a little messing around to verify audio levels were right. I selected unfiltered audio, and squelched audio, to “help” the TNC determine whether the channel was active or not – it seemed that too much noise inhibited transmit, though I may have been mistaken.
As a test for operation, I disabled smartbeacoming, and turned on a “transmit every 10 seconds” beacon. This allowed me to at least see the unit working, and observe the audio on a nearby radio. I think I’m in a bit of a low spot, so hitting any nearby digipeater is difficult.
I used SDRAngel and an RTL SDR with the analog RF demodulator feature to observe the RF spectrum and set the level to something reasonable. I could attenuate the snot out of it (46.5 dBm into 100 dB or so of attenuation should take this to a level that won’t overload a typical SDR – more here on that) – but I chose a quick and dirty on-air test. I’ll work on that more later, if I can’t get a successful on-air test in range of a digipeater.
I’ve updated my wiring diagram to show some pinouts, and show where things stand.
- USB cable works for talking to the XPR Radio
- 12V to 5V supply works for all of it
- GPS data into the OT3m works
- Port A (TTL levels) works from the current BLE module to and from the T3m
- Audio out from the TNC to the Radio works
- Audio from the Radio to the TNC has not been fully tested.
With all of this progress, I’ve ordered a pile of perf boards, headers, and an enclosure – it’s getting on time to box this up for actual operation. BLE is the next task. My intent, once I have the main functions working, will be to put this in a box that simply has a gland for the XPR accessory cable, and an SMA cable. I may put some switches on the board internally, so I can pop the cover for testing – interrupt power on any of the devices, maybe even some headers so I can plug in an Arduino to test data flows.
I’ve got a bit of time on the road tomorrow, so I moved the whole setup to a little nicer (and smaller) board. …. Let’s see how it does on a shakedown when I can hear some digipeaters and other stations:
Some References that I’ve used to get this far:
- XPR PLMN5072 Accessory Connector Guide (with pinout)
- Argent Data Systems T3Mini Data Page (with pinouts)
- KISS over BLE Spec on Github
- KISS over BLE for APRS.fi (another Github page)
- AT09 BLE Modules (“HMT MLT-BT05”) – these didn’t work for APRS.fi, but did provide some learning and testing opportunities
- HC06 BLE modules – these didn’t work with iOS either, these were the first ones I bought
- BLE Module AT+ Commands (instructables)
- Using Arduino as a USB to (TTL) UART Adaptor