MicroAPRS is an APRS firmware for MicroModem. It supports both normal KISS mode, and a simple serial protocol for easy communication with an Arduino, or other MCU.

You can buy a complete modem from my shop, or you can build one yourself pretty easily. Take a look at the documentation in the MicroModem repository for information and getting started guides!

• Send and receive AX.25 APRS packets
• Full modulation and demodulation in software
• Easy configuration of callsign and path settings
• Flexibility in how received packets are output over serial connection
• Persistent configuration stored in EEPROM
• Shorthand functions for sending location updates and messages, so you don't need to manually create the packets
• Ability to send raw packets
• Support for settings APRS symbols
• Support for power/height/gain info in location updates
• Ability to automatically ACK messages adressed to the modem
• Can run with open squelch
• Supports KISS mode for use with programs on a host computer

When the modem is running in KISS mode, there's really not much more to it than connecting the modem to a computer, opening whatever program you want to use with it, and off you go.

If you want to use the SimpleSerial protocol, here's how to control the APRS modem over a serial connection. The modem accepts a variety of commands for setting options and sending packets. Generally a command starts with one or more characters defining the command, and then whatever data is needed to set the options for that command. Here's a list of the currently available commands:

##Serial commands

To set your callsign to XX1YYY-5, and then save the configuration, send these three commands:

cXX1YYY
sc5
S

To send an APRS message to ZZ5ABC-1 with the content "Hi there!", send these commands:

mcZZ5ABC
ms1
#Hi there!

To send a location update, with the comment "MicroAPRS", you can do something like this:

lla5230.70N
llo01043.70E
@MicroAPRS

To send an APRS message to ZZ5ABC-1 with the content "Hi there!", using a raw packet, send this command:

!:ZZ5ABC-1 :Hi there!{01

Here's an example of how to send a location update with power, height and gain information, using a raw packet:

!=5230.70N/01043.70E-PHG2410MicroAPRS

When saving the configuration, it is written to EEPROM, so it will persist between poweroffs. If a configuration has been stored, it will automatically be loaded when the modem powers up. The configuration can be cleared by sending the "clear configuration" command (C).

To connect to the modem use 9600 baud, 8N1 serial. By default, the firmware uses time-sensitive input, which means that it will buffer serial data as it comes in, and when it has received no data for a few milliseconds, it will start interpreting whatever it has received. This means you need to set your serial terminal program to not send data for every keystroke, but only on new-line, or pressing send or whatever. If you do not want this behaviour, you can compile the firmware with the DEBUG flag set, which will make the modem wait for a new-line character before interpreting the received data. I would generally advise against this though, since it means that you cannot have newline characters in whatever data you want to send!

The project has been implemented in your normal C with makefile style, and uses AVR Libc. The firmware is compatible with Arduino-based products, although it was not written in the Arduino IDE.

Visit my site for questions, comments and other details.