Tonight I attended the Surrey Geeks Meetup in the lovely offices of the generous Kyan in Guildford. The topic was essentially anything to do with Raspberry Pi and Arduino. There was some pretty innovative stuff being talked about.
The organiser, Jon Nethercott, kicked off talking about the Arduino boards and the projects he had constructed, including an amazing capacitance meter that required no additional hardware. You could push a capacitor into two A-D pins and the display shield would quickly tell you what value it had, from 1pF up to hundreds of uF.
It has two ways of calculating the value: from 1pF to 1nF it measures the ratio of the capacitance of the test capacitor against the residual 25pF capacitance of the internal circuitry! I've done a lot of electronics in my early life (really early life - I built my first computer in 1977 using the 1802 CMOS microprocessor), but I've never, as far as I recall, had to work out the voltage distribution of two capacitors in series!
Jon explained it to me, and it actually works out quite intuitively - the bigger capacitor develops the smaller voltage, as from an electron point of view, it is similar to a lower resistance, as it has more "space" for electrons to flow into it.
Above 1nF, which is very large relative to the 25pF residual capacitance, Jon switches to an alternative technique using an internal pull-up resistance to charge the test capacitor, then measure the developed voltage and time taken to reach it. Once again, not a scrap of extra external circuitry since it relies this time on an internal resistance. Cool.
Related to the work I've been doing, Richard Jelbert showed us his Pi for cars with a BLE beacon attached. This could be used to drive an app on the driver's phone to pick up a small number of events broadcast from the Pi, including from sensors. For example: when the driver enters the car, starts it, stops it .. or crashes it! This could be used to reward clean drivers with lower insurance, without any inconvenience to the driver, who otherwise has to keep messing with the app controls at the start and end of the journey.
Richard also showed us his prototype for a Bitcoin vending machine. Seriously: a Bitcoin vending machine. You put in some cash and get a printed slip with two QR codes on it: the public and the private key for your entry on the blockchain.
My colleague in government and another meetup organiser, David Carboni, told us of his plans to enhance local neighbourhood safety with an automatic number plate recognition system. Every participant in a street would have Pies tracking cars via its camera. They could share the information to track stranger cars. The approach would involve quite a bit of image processing to normalise the image then extract the characters. There is this software which may be interesting to look at.
Next up, a Research Assistant from Guildford University, James Mithen, told us of his plans to get into ARM code and write another operating system for the Pi, as a fun exercise...
Finally, I stood up and told everyone about the Augmented Reality Internet of Things idea, with a mention of Minecraft house-modelling to get them all thinking I'm a nutter. It worked. They did.
We all talked more than we hacked or wired, which was great - and there's always next time to play with kit.
Really exciting stuff. And great pizza and great beer. Thanks to the organisers and hosts.
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