I’m working on the design of a APRS Tracker transmitter. The dream is a self contained radio transmitter, modem, and controler with a bluetool connection to a tablet running Xastir.
There are lots of designs and APRS Trackers. Some are almost what I’m looking for. Many are out of date or the designer is dormant. The bigest example is MicroModem. Wounderful design from 2014 but the deveoper is… In his how words… “Long Time, No See”.
The AP510 AVRT5 is exactly what I’m wanting but it has some very bad review.
I purchases a Mobilinkd. It has everything but… GPS for “off line” tracking and Open Source Hardware. Mobilinkd is made to work with APRSdroid. You Android phone or tablet provides the GPS information and the tracking logic. Connects to the modem via BlueTooth and has cable for almost every kind of radio. This is nice buy I ask myself why it is needed at all when APRSDroid also works as a sound card TNC. All you need is a radio with VOX or a VOX curcit to key the radio.
Then there is Tracksoar. This is a very small tracker with gps and radio. It’s all opensource and open hardware. This project is very alive and perfect for a balloon project. But, receive and bluetooth are missing.
Some of these designs use a resistor network and for data pins to output a 16bit sign wave. Others use the pulse width modulation (PWM) out of one pin and a low pass filter. PWM works good and because I uses less data pins this is preferred.
For my build I’m breadboarding with a Arduino Nano, a HC-05 bluetooth and a NMEA compatible GPS. The radio output will be SA818V or DRA818V. The transciver is 1W. (https://www.youtube.com/watch?v=vetZwme2lhk)