Raspberry Pi/Echolink/SVXLink Naked Node
By: Ramon Gonzalez (KP4TR)
Welcome to the Raspberry Pi/Echolink Naked Node page! After playing with the pIRLP Naked Node design for a while, I found myself with many radio parts, bolts, screws and an extra Baofeng BF-666S that I had used on one of the first prototype nodes I built a few months ago.
I recently went to Puerto Rico to visit family, and decided to leave my IRLP Naked Node 8205 as a remote experiment to play with. I can access the IRLP Naked Node using my Remoterig setup so I can have access to IRLP when visiting there, and use it as a remote base. But now I didn’t have one here in Florida to play with and take around and show friends and use while traveling. I did some inventory and had all the parts to build an extra Naked Node, but had one missing piece that is not easy to get. It was the IRLP board itself.
IRLP is a great system, but wasn’t designed for extreme experimentation. It requires a proprietary IRLP board that cannot be duplicated. I couldn’t spend any money on yet another IRLP board. SO I decided to see what I could do to re-use this hardware on another platform.
Allstar is a great and extremely flexible VOIP system, but it has not been fully ported over to the Raspberry Pi platform (as of August 2013), even though Asterisk itself has. So when this occurs (porting to Raspberry Pi) , I’ll look into it.
Echolink for the Raspberry Pi has 2 options that I’m aware of. There is TheLinkBox and SVXLink. I found much more information on using SVXLink with examples, and it seemed to be closer to what I was looking for. TheLinkBox supports the GPIO connector on the Raspberry Pi for PTT, but I saw no information on how to use a COR/COS via the GPIO (if possible) and using VOX is out of the question. SVXLink does not support the GPIO connector yet (August 2013), but fully supports squelch COS, PTT and even CTCSS squelch, as well as VOX using a serial port. So I went with SVXLink.
I downloaded Debian Wheezy for Raspberry Pi, configured an SD card, and got the SVXLink source code and did a build from scratch, using the options to run on the Pi platform. No issues building it at all, and pretty straightforward to do. I ordered a serial port sound card interface board (see pictures) from Advanced Repeater Systems. The board is pretty straightforward in its design and perfect for my needs because of its size and exposure of multiple soldering points. See schematic here.
The Serial EchoLink Adapter requires a serial to USB cable, and the existing ones looked too big and would occupy too much space. So I decided to replace the RS232 DB9 port on the board and ordered a DB9-USB-F Modules from FTDI. See the technical document from FTDI – Upgrading a passive DB9 RS232 Interface to an active USB Interface using an FTDI DB9 – USB – RS232 Module. This is how the modified board looks.
The serial port is used to detect COR/COS from the radio via the CTS pin 8, and to generate PTT for the radio via the RTS pin 7. The Echolink board is designed to receive COS by pulling CTS high. The problem with the Baofeng BF-666S radio is that COS is generated from an audio chip that produces +3v and seemed to not be enough fro the SVXLink to detect squelch input, so I modified the board to use a buffer and pull the pin to ground. See the modified board.
I removed R33, D24 and R34, essentially cleaning the path to COS input to the serial port. Using a NPN transistor 2N2222, I placed it in the holes as seen in picture. This allows the emitter to ground, base to input from radio, and collector to pin 8 (CTS) of serial port. In the space where the green LED D24 was occupied, I placed a jumper. I later replaced the jumper with the resistor removed from R34 which places a resistor to emitter side of transistor.
As for the radio, Raspberry Pi, and the step down transformers for the radio and Pi, see picture. These are the same radio and design from the KP4TR Pi Naked Node.
We assemble the components together, and wire it all. When completed, we have a complete Echolink portable node with radio, interface, computer and sound card all in one, and only requires 12V and a connection to the internet cia the Ethernet cable. We would have liked to use a wiresless Edimax USB card, but we have no space available on USB ports and adding a USB hub would require a powered hub and make this design a bit messy.
See the following video below.