Software Defined Radio hacks

The radio meteor project was great but has a few hang ups that are bugging me...

1. The hand-held yupiteru radio has some issues with frequency stability that makes it difficult to work out what's a satellite and what's a glitch in the radio.
2. The radio/soundcard interface seems to be susceptible to RF interference - eg from my computer monitor! This creates noise and false alarms on the meteor counter
3. To detect meteors, my PC must be on and running the speclab software with the radio attached. This is tedious and uneconomical to run 24/7
4. The feedline from the aerial to the radio is about 15m long. This may cause line losses (ie the signal gets weaker)

So to fix these I'm planning on using a digital tv USB dongle and an arduino to create a detector-in-a-box that could run off a low-wattage wall-wart and could dump data onto a USB stick or live stream over wired or wireless network onto the internet...

Fun, eh?

The system relies on a modern miracle chip built into some brands of USB digital TV dongles. The realtek Software Defined Radio (SDR) lets you tune into a huge range of frequencies (around 70MHz to 1.7 GHz). I got a generic one from Amazon for £17. There are a few sites around that list compatible dongles.

More to come on HDSDR and how to grab the data coming off the dongle...

Raspberry Pi as a Cosm data server

Part of concept I'm working up uses a base station to act as the bridge between a suite of sensors and the internet. Cosm is a web service that manages data upload, storage and retrieval and enables sharing of data streams.

Getting data off the Pi and into Cosm is reasonably trivial, but it took me a few tries to get it working, but here's the Cosm datastream. The Pi is hooked up to a BMP085, as described previously. In the end I bought an Adafruit cobbler for the convenience of hooking up to a breadboard and popped the Pi in a crust of laser-cut clear acrylic.

Raspberry Pi

Pi Power

After getting my Pi a few weeks back I've been struggling to get it further than the stock X windows GUI, let alone doing anything interesting with it. Part of the problem is having to dig out a PSU, keyboard and mouse and sitting in front of the telly with the Pi's composite out plugged into the TV AUX (all at a time when small people were cleared from the vicinity of the TV).

So I got the latest Occidentalis distro from the fantastic Adafruit Industries who built in a few handy utils and libraries (like SSH and libs to enable access to the GPIO pins). After a few test runs from the floor in front of the TV, I hooked the Pi up to my router with an ethernet cable and powered it up. Using SSH on my Linux netbook is straightforward, but you need extra software for Windows - PuTTY works well enough (although the connection has to be reset occasionally - not sure if this is the router, Pi or PuTTY...)

Next I got hold of my BMP085 pressure/temperature sensor breakout board, which uses the I2C bus to communicate with other devices. The Pi has built in I2C support brought out on the GPIO pins (one data and one clock pin for each I2C bus). Again, Adafruit have made a library and set of example programmes for interfacing with the BMP085 (amongst other things!). Connection to the GPIO pins at the mo is through an old IDE cable and hook-up wire. The Pi has 3.3V and 5V outputs right next to each other - so be careful connecting up 3.3V devices! Eventually I will make a breakout board, or buy one...

Currently I'm attempting to use Cosm to publish this data, but the examples in Python are defeating me at the moment.

New tabs

To try and organise my projects, I'm using the blogger 'pages' view. There are new tabs with an introduction and ongoing projects (here and here)

Mantis-a-like CNC miller, build part 1

I'm going from fuzzy ideas and sketchup models to actual hardware now... After sourcing silver steel from these chaps in Wales (and most of the bolts, leadscrews, nuts and a few washers...) I grabbed a lump of MDF from Wickes and started building on Saturday...

The mutt is for appreciation of scale.

DIY CNC milling machine

...or cartesian robot.

I've been researching building my own CNC mill for a few months now (read: trying to decide if its too much hassle to make my own or to save up £500-1000 and buy one...). In that time I've bought a few cheap stepper motors from Ebay and even a couple of 99p scanners and printers to disassemble for parts. I started putting together a motor driver board based on three L293D chips, an output multiplexer (need five digital lines per axis channel, three axis add up to 15 channels) and an ATMEGA328P (with Arduino bootloader etc)

I'm now at the stage where I need materials too build the system. This is the tricky bit as I don't have a workshop or any bench tools. So I looked around for DIY builds that were simple in their approach and that didn't need fancy machining or (too much/accurate) metal cutting.

Two options presented themselves:

Profile aluminium/aluminum section to create the frame (pros - easy to build up, Al is fairly easy to cut to size and drill and will provide a stiff frame. Cons - cost, once you add up all the section and fixtures. Difficulty making a cost effective linear slide without resorting to expensive rail-and-truck systems)

Wood (pros - really cheap, easy to cut, can glue, screw bolt or whatever suits. Cons - not as stiff, may deform over time, looks a bit rubbish)

A couple of example designs:

Aluminium section frame design with linear rails and trucks

Wood design using silver steel rods and Oilite bushes

After finding the mantis CNC machine design, I decided to go with wood and the desgin above.

A few design considerations:

• The linear bearing is basically a pair of hardened, ground steel rods with Oilite (oil impregnated) bushes glued to a wooden truck. It would be really easy to misalign these rods and jam the axis movement.
• Stiffness of the design is OK for a wood structure and the steel rods help to reinforce it, but there still may be a few mm flex, particularly on the y-axis (green truck)
• The maximum cutting area is around 150mm in X by 225mm in Y by 75mm in Z. 
• The end-mill motor will probably not be very powerful, but OK for milling copper clad board or wood. Hopefully it'll do aluminium as well :)

 Oh, a note on the steel rods - in the UK you can get something called 'silver steel' which is like 'tool steel' elsewhere. This stuff is intended for making tools (duh) and is fairly stiff. It is ground to a reasonable precision making it better than stock steel rod intended for machining to size. I hope.

First build update here

Radio meteor detection

OK so its been a while since I posted up here...

I've been busy with work, children and other distractions resulting in a neglected blog :(

There are a few projects on the go at the moment, but I'm going to put up some details on detecting meteors using a PC sound card, a handheld radio scanner and some wires :)

The end results look a bit like this:

These screens are generated by SpecLab. The bright blobs on the top left are meteor trails. There is a great website here that explains what the blobs might mean. Basically, anything travelling left-right is showing a doppler shift (ie speeding up or more likely for a meteor - slowing down). Anything that appears in a vertical line is persistent over time. The vertical bands are radio interference (I think!) Occasionally there are tracks that might be satellites, but to be honest I don't really know!

More to come on how this was put together...