APRS with the Raspberry Pi and the TNC-X board: Unterschied zwischen den Versionen

Version vom 27. Dezember 2015, 20:58 Uhr

1 Motivation

After my first series of experiments with APRS and Arduino, but also with APRS and OpenWRT I am now trying out something else:

Using a Raspberry Pi as a APRS gateway. In this case I intend to do it bidirectional.

2 The TNC-X board

• http://tnc-x.com/
• Details on the version for the RPi: http://tnc-x.com/TNCPi.htm
• Schematic Diagram // TNC - Pi Assembly Instructions & Operating Tips : http://tnc-x.com/TNCPi.pdf
• Documentation: http://tnc-x.com/documentation.htm

3 Notes on the Raspberry Pi board and other boards in the setup

The RPi 1B version which I used has a couple of problems. Notably the USB socket is very high, which gives you a few problems connecting other boards. Stackable shields will easily have shortings wo the ethernet socket. So this is a mechanical issue you will have to solve.

I did it by simply soldering out the USB socket. In case you still need USB connectivity, you will need to attach some angled stacked pins.

As in most of my RPi projects I am using the pin header for power supply. I generally do not use the usb socket, because that seems a little unreliable to me.

For the power supply I am frequently using DC/DC converters from Ebay, you get them cheap from China.

Here in this case I was using two converters, one from any high voltage up to 30V down to 7,5 for the IC2E clone and another one for the step from 7,5 down to 5,0V for the Raspi.

I also attached a serial port socket using a MAX3232 converter, firstly to ensure access to a raw Raspian image, but secondly also for diagnostic actions on the serial line.

The little pcb in the middle between the Raspberry setup and the radio is a PTT arrangement: The TNC puts a DC voltage on the PTT pin, which must arrive on the TX audio pin of the radio, though, with a considerably high impedance. So a 4k7 resistor will help. The TX audio signal must be given to the same pin, however de-coupled by a capacitor, I am using a 0.1 Microfarad.

Here is some info found on the web about this setup:

 The IC2E can be used successfully on packet. This is how to achieve it.

TNC                             RIG

PTT-----------4.7K-------- TIP OF SMALL JACK

TX AUDIO------0.1MF------- TIP OF SMALL JACK

GROUND-------------------- BODY OF BOTH JACKS

RX AUDIO------------------ TIP OF LARGE JACK

This arrangement works with most TNC2 type clones, but it has not been tried
on the PK88.

Another possibility would be to use a 1 to 1 audio isolating transformer.
This is a suggestion on how to connect it up:

RX AUDIO---------TIP OF LARGE JACK
GROUND-----------BODY OF LARGE JACK
GROUND-----------TRANSFORMER PRIMARY
TX AUDIO---------TRANSFORMER PRIMARY
PTT--------------TRANSFORMER SECONDARY
                 TRANSFORMER SECONDARY---------TIP OF SMALL JACK

When the PTT line goes low, it makes the Tx connection for the IC2E.

Julian G6LOH @ GB7BIL

4 The Radio used

• I am using a IC2E clone.
• Here is the manual: http://www.radiomanual.info/schemi/IC2_user.pdf
• Here is some more insight on the cable type, when connecting a regular TNC (Cable Type 1): http://www.symek.com/d/afskkabel.html

5 Configuration

First of all: This site was very helpful: http://www.auetal-online.net/page3,0,0.xhtml

• Note that it is really important to set jumpers Nr. 3 and Nr. 4. Otherwise you won'r receive anything and you will not be able to transmit either.

• I was downloading the following APRX version:

wget http://ham.zmailer.org/oh2mqk/aprx/aprx_2.08.593-1_armhf.deb

Here's the APRX config:

mycall  DB0HSR-1
myloc lat 4859.93N lon 01205.59E
<aprsis>
passcode 12345
server    rotate.aprs2.net
</aprsis>
<logging>
pidfile /var/run/aprx.pid
rflog /var/log/aprx/aprx-rf.log
aprxlog /var/log/aprx/aprx.log
</logging>
<interface>
  serial-device /dev/ttyAMA0  19200 8n1    KISS
  callsign     $mycall  # callsign defaults to $mycall
  tx-ok        false    # transmitter enable defaults to false
  #telem-to-is  true # set to 'false' to disable
</interface>
<beacon>
beaconmode both
beacon symbol "I&" $myloc comment "Tx-iGate Raspberry/TNC-X/APRX"
</beacon>

6 Future Plans

So this project really worked well, and APRX allows transmitting, so that is really a great benefit. I will try to extend this project by the following terms:

• build two more of them, provide them to DB0MHB and to DB0KN and create greater coverage
• add some telemetry with a temperature and humidity readout. I will need to think about the connection, because I removed the USB socket for space reasons, as you can see on the pictures below.

7 Images

8 Links

• http://www.nq0m.com/2012/09/03/aprs-i-gatedigi-with-my-new-raspberry-pi/