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£1,330 pledged of £1,800 goal
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By Jenny List
£1,330 pledged of £1,800 goal
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About this project

For more information:

Future updates to this project, and how to get your hands on one will appear here: http://www.languagespy.com/electronics/

What is it?

An expansion board supplied as a self-assembly kit, designed for experiments with the Raspberry Pi as a radio frequency source or radio transmitter using the programmable clock generator built into the Pi's processor.

An assembled kit
An assembled kit

Who is it aimed at?

This kit is aimed at radio amateurs and electronics experimenters with an interest in radio.

It has plenty of scope for interesting the Pi's primary audience of younger people in the world of electronics and radio by showing them that a Pi can achieve long-distance communication and talk to something in the real world rather than on a breadboard.

Background

The Raspberry Pi clock generator is a powerful frequency synthesiser which can generate frequencies up to 250MHz at the Pi's 3.3v logic levels. This is enough to provide a useful RF signal source for experimentation, or given suitable filtering and antennas to allow the Pi to be used as a low-power radio transmitter by users with an appropriate licence. 

The kit brings the clock generator as well as three GPIO lines and the 3.3v supply to solderable headers on a PCB. It also provides a BNC socket for RF output, and a DC blocking capacitor to protect the Pi processor from damage. A prototyping area is provided for the construction of RF filters or transmitter control logic.

What you will get

The components of the kit
The components of the kit

The kit will be supplied as a self-assembly kit of four parts, the PCB, GPIO connector, BNC connector, and blocking capacitor. The kit instructions cover assembly and software, and provide pointers and background for filter design (See update number 4 for more details on filters). Soldering skills are required for assembly.

Compatibility and software

The clock generator appears in both BCM2835 (A, B, and B+) and BCM2836 (Pi 2) Raspberry Pi boards, and this kit should work with all boards except the Compute Module development board which does not have the standard GPIO header. This kit will not work with single board computers from other manufacturers that use the Raspberry Pi form factor. 

The open-source community has produced several pieces of software for experimenters using the Raspberry Pi clock generator. There are signal generators, FM transmitters, and WSPR beacons for amateur radio. With a low-pass filter on this board and a dipole antenna the 10mW of RF produced by the Raspberry Pi WSPR beacon can be heard thousands of miles away. The table below shows some reception spots we've seen for our Raspberry Pi on the 20m amateur band here in the UK. At the top is K9AN in Illinois, a distance of 4001 miles.

WSPR spots sorted by distance, furthest at the top.
WSPR spots sorted by distance, furthest at the top.

At the time of writing not all community software supports the Pi 2. This is due to the BCM2836 having a different internal address for its GPIO than the BCM2835 rather than a fundamental incompatibility. Some GPCLK0 software already works on the Pi 2, and we will be spending some time working to extend that support while this campaign is running. 

UPDATES: We have produced a Raspberry Pi 2 version of Jan Panteltje's freq_pi signal generator, which can be found at this link on GitHub, and an SSTV transmitter for both Raspberry Pi versions which can be seen in project update 3.

This kit does not include any software but its instructions name some of the more popular packages and provide links to the code. If the kit is being used as a radio transmitter then it is the responsibility of the user to ensure that they possess the relevant licence for their transmission.

Shipping to anywhere in the world is included in the rewards, however you are responsible for any local taxes or excise duties payable in your country. 

Progress so far

Prototype boards
Prototype boards

The first RF breakout was built on a general-purpose prototyping board in early 2015. In May 2015 a PCB was designed and a small run of prototypes was made with and without different filters. These boards were then tested as WSPR beacons on VHF (4m) and HF(20m) and proven to be effective.

Timing

Some of the components used in this kit have a bulk lead time quoted as between four and six weeks. We would therefore expect to start shipping rewards more than six weeks after a successful conclusion to this campaign and receiving the funds from Kickstarter. Thus you should expect to see your rewards around the middle of October 2015.

Risks and challenges

We have proved with our prototypes that the kit works as expected and that our component suppliers can deliver the goods in small numbers. Though a low component count minimises supply risk there is still a possibility that the quoted lead times for larger orders of our components could be exceeded or that we could be supplied with faulty PCBs or other parts. If this proves to be the case we will secure returns or replacement parts, however this would incur a delay to our shipping date. It's a remote possibility, but we have to point it out.

We are a small organisation with some experience of product fulfilment in the software industry so we think we have accounted for all eventualities when getting your rewards to you. In the happy event that this kit proves to be hugely more popular than we expected though it will place a strain on our resources and it may take us longer than we anticipated to ship your rewards to you. In that event we will provide regular updates as to our shipping progress and we will work as hard as we can to ship your rewards as soon as possible.

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Funding period

- (30 days)