aprs <--> trbo with [crossband] voice

[kc9uhi]

New spring project: interface a mototrbo radio with a raspberry pi and two analog vhf/uhf radios for the purpose of providing a mobile (cross)band repeater and aprs location/messaging service.

This project on github (https://github.com/KD8EYF/TRBO-NET) provides location updates and two-way messaging between APRS-IS and a MOTOTRBO radio/network. I plan to utilize that on a raspberry pi to allow a DMR HT to provide GPS location updates to APRS. Also, I'll interconnect the MOTOTRBO radio and a standard amateur dualband mobile radio to provide analog voice link.

Diagram of the project:

[kc9uhi]

For my setup, this is what will be used:

-HT: XPR6550 UHF (gps & message capable)
-MotoTRBO Radio: XPR4300 (got one cheap on ebay)
-Motorola MotoTRBO rear USB interface cable (modified to provide TX/RX audio, PTT, COR) see pinout
-iCOM 208-h dualband radio (existing, for voice)
-Raspberry Pi Model B running raspbian
-TRBO-NET by KB8EYF
-APRSC (internal aprs-is server to bridge TRBO-NET and APRX)
-APRX
-Existing Tracker3-mini and garmin nuvi 2555 gps setup w/ maxtrac radio (aprs rf)
-VHF/UHF diplexer to utilize existing dualband antenna with uhf xpr4550 (currently used only by vhf aprs radio)

[kc9uhi]

KD8EYF TRBO-NET software is written in perl, and quite well laid out for further expansion.

It has the capability of parsing incoming text messages from the DMR radio - can currently then execute internal commands (cmd), lookup last known location of a callsign (who) or send aprs messages (aprs). Might add additional capabilities, such as low battery warning.

Messages from other programs running on the computer (pi) can be sent by writing them to files in a spool directory. Provisions from group messaging also exist. Still trying to figure out how this works.

[kc9uhi]

Found this to power the pi from 12v car power. Built in micro USB plug, high amperage 5v output.

RioRand DC DC 8-50V 12V/24V/36V to 5V 3A Buck Converter Regulator MICRO USB Adapter Connector Power Supply Module Waterproof https://www.amazon.com/dp/B00KUNPJS0/re ... -ub0PR7MK0

Much simpler than the rc car 5v converters I found last year from China.

[kb9mwr]

I bought a similar type of buck converter, so that I could have a high current 5 volt source from of my Astron.

Mine didn't have the micro usb plug. No biggie though, I just wacked one off something laying in the junk box.

[kc9uhi]

Programmed up the xpr4300 today, connected via usb cable to pi. Successfully sent/received txt messages from xpr6550, with pi connected to aprs-is.

Next step is to rig up interface from pi to tracker3-mini for aprs-rf link.

[kc9uhi]

Had issues with the GPS conversion formula in the TRBO-NET software. Latitude was spot on, but Longitude was way off. Was calculating out to somewhere in western wisconsin. Took the average value of several GPS posits from the raw data stream (somewhat mapped out in the source code) and calculated a new conversion factor. Taking the radio out for a drive this afternoon to gather some more data in hopes of validating the new conversion factor.

[kc9uhi]

Fixed the GPS conversion.

Travel was being mapped opposite of actual movement. The software was reading the GPS data as an unsigned int, whereas the data was actually a signed int. Signed int is encoded using two's complement binary, which is pretty much opposite of unsigned int. Thus, the opposite mapped data.

Recalculated the conversion factors with the new data, went for a test drive, and all works well.

[kb9mwr]

So when are you going to be in Green Bay next to show this off?

[kc9uhi]

Minor setback. Went to build the audio interface cable, and the accessory jack on the xpr4300 uses a different metal contact than the maxtrac connector. Ordered, waiting for those to come in.

23Apr15 Update: parts arrived today.