Building a Raspberry Pi
IRLP Node

See my second Pi IRLP node 8891 in Cape May, NJ

The Raspberry Pi is a small single board computer which runs a Debian Linux package called Raspbien compiled for its ARM processor. The board includes two USB ports, HDMI video and sound, Ethernet, GPIO, and an SD card slot for the operating system.

It has all the necessary ingredients to make a small, low power IRLP node. For IRLP the GPIO is interfaced to the IRLP boards 25 pin D connector and a USB sound FOB provides the transmit and receive audio.

The first place to start is the Pi IRLP web page - http://www.irlp.net/pi/

There you will find links to photos and details about installation. You have many options on how to put a system together from buying a totally pre-configured plug and play system to using parts you already have. The only requirement is the IRLP board which can be purchased at the Pi IRLP webpage or if you already have a board it can be modified very easily for the Pi. The modification requires the installation of one jumper and the removal of a diode.

In my case I only purchased the modified IRLP board at the website. The USB FOB can be ordered from Amazon or other vendors for about $9. The cabling can be fabricated if you have or can get the required connectors. Note that the DB9 cable assembly which carries the radio signals comes with the purchase of the IRLP board.

The Raspberry Pi is available from many sources for about $35. The power supply and cable are about $12. The SD card from $8-$14. I used a SanDisk Ultra class 10 8Gb microSD which came with an adapter. It was about $13. You can buy cheaper SD cards but beware that there are a great deal of counterfeit cards out there that look like the real thing. There are also cheap substitutes. Spend a little more and buy at a reputable store. Also buy a second one for a backup.

The first thing you will do if you are not buying the pre-configured SD card is download the latest Raspbien software. The downloads are available at - http://www.raspberrypi.org/downloads

Download the Raspbien "Wheezy" image. You can do this on a Windows or Linux system. I use Windows. The downloaded image file will be written bit for bit to the SD card you purchased. The card does not have to be formatted in any way and any data previously on it will be overwritten. I used win32diskimager which is available for download at many sites. You simply insert the SD card in a card reader/writer attached to your computer and write the image to the card. Once written it can be inserted into the Raspberry Pi (with the power off) and it will boot right into the Raspbien graphics display. If this is your first time using the Pi you may want to play with it a little before installing IRLP.

Linux uses a directory and file structure similar to DOS and Windows but the commands and syntax are not the same. I have been using it for over 20 years and it comes naturally to me but for those that are using it for the first time it has a learning curve like anything else. A starter book like 'Linux for Dummies' might be a good place to start. While there is no real requirement to know Linux to operate a node it will make your life easier when you want to change things on your system.

To install the IRLP system follow the directions here - http://www.irlp.net/pi/directions.txt

This will walk you through all the steps required to install the software and get your node up. If you are doing the install yourself your new node number will be assigned once it is determined that you are a valid amateur radio operator and that you purchased the IRLP board. This usually only take a few hours but it is a manual operation involving real people so it could take longer.

After you get your node on the air you undoubtedly will want to make changes to suit your needs. Any changes are stored on the SD card and failure of the card would require going through the install procedure again. So once you are confident that the system is working properly make a backup copy of the SD card using your Windows or Linux system to read the card image and write it to another card. Do this every time you make more than a minor change. It is not necessary to write another card every time you read an image as long as you maintain the images on another system. Making these copies as you go along allows you to go back to any previous version should something go wrong.

When using the Raspberry Pi there are a couple of things you should remember. NEVER insert or remove an SD card with the power on and always shutdown Linux before removing the power. This can be done by logging into the system via SSH and issuing the command 'shutdown -h now' and waiting for all activity to cease before removing power.

Once your system is running your will want to put it all in a box. Below are photos of how I mounted my system in a plastic hobby box with aluminum front and back panels. I cut an aluminum baseplate for everything to mount on. LED's on the front panel give system status and the radio, Ethernet, and power connections are on the back.

I hope you have fun with your Raspberry Pi IRLP node. I have with mine and it works very well. I would be glad to answer any questions. Please send them to my email address at QRZ.

Photos

(Click any photo to see a larger view)

IRLPRear Panel View, DB9 radio connector, SD card Slot, Micro USB power connection and Ethernet (red cable) connection. The coaxial power connector is for future 12V power in mobile operations.
IRLPOverall inside view showing Raspberry Pi, IRLP board, USB sound FOB, and interconnecting wiring
IRLPRaspberry Pi Board. Soldered wire connections are for front panel LEDS
IRLPIRLP board, Soldered wire connections are for front panel LEDS
IRLPFront Panel View, Leds (l-r) PTT, COS, DTMF, Internet activity, SD card activity, Power
IRLPPreparation of the flat cable for soldering to the DB25 connector.
IRLPCable showing the 26 pin flat cable connector attached.

The connection between the Pi GPIO connector and the IRLP DB25 connector requires a 26 pin flat cable connector on the Pi end. This connector is pressed onto the wire. The other end needs to be prepared for soldering. Not all of the pins or wires are used. See the schematic link below for wiring information and follow these photos and those on the irlp.net/pi page. A completed cable assembly is also available for purchase there.

IRLPDB25 connector to the Pi board showing side one connections.
IRLPDB25 side 2 connections.

Links

A note about SD cards

There has been much written about problems with the Raspberry Pi and SD cards. I have never had a problem with my Pi's even after numerous unscheduled power losses. I do use a better quality card typically a San Disk class 10 Ultra 30mb/s 200X 8gb card. They generally cost about $11-$14 but you might be able to find it cheaper on sale.

Finding the cheapest card is not a good idea for several reasons. First of all there are a lot of counterfeit cards on the market. They look like and are packaged like the real thing. The cheaper cards are also slower. The system will boot and operate faster on a higher rate card. The Pi can be overclocked and I typically use the modest overclock setting.

A faster card will also read and write faster on a card reader/writer. I can typically write an 8gb image in about 5 minutes. This, of course, is also dependent on your card reader, computer, OS, and card reader software.

The issues with Pi SD cards seem to be associated with improper power down, not shutting down Linux before removing power. While it is not generally a good idea to do this on any system in some cases the Pi apparently has more of a problem. Again I have not seen or been able to recreate this on my systems.

It might have something to do with the power supply used and how it shuts down when power is removed. I run one of my Pi's on a wall wart 5V 2A Powergen switcher and the other is run from 12 volts through a 5 volt three terminal regulator.

Another potential problem with SD cards is that they have a limited write cycle. When I say limited it is measured in millions of write cycles so it is fairly large. A write to a single location eventually wears out that location. I have never had an SD card fail due to this. Not to say it can't but I don't think it is something one should worry about as long as you are not doing anything to hasten it.

On the Raspberry Pi when using IRLP the cache is turned off so unless a file is specifically written to the SD card there is no write activity to it. This would generally be when a log file is written or file updates take place or you edit a file. If you did 1000 writes a day to a specific location it would probably take several years to make that location fail.

One area where the SD card is continually written is when the CWID code distributed with the Pi is used. Because of problem with sound mixing the CWID is written every time the CWID is announced. I moved the CWID script to the custom directory and modified it to write my CWID to a sound file just once. All subsequent ID's are only read from the SD card as a sound file. There is a note in the script that this would be fixed in the future but I don't know if it has in the main distribution. Copying this or any script or code into the custom directory prevents it from being overwritten during an update.

To summarize the key points:

And finally understand that as long as you have a backup the issues with SD cards and the Pi are minor compared to a hard disk failure or many of the other things that can happen with any computer.

This page last updated 7/7/2013

© 2013 - WA3DSP