In 2006 I reckoned that a simple vario could be put together with a pressure sensor, bluetooth transmitter, power supply and microcontroller. I imagined that the device would transmit pressure data to a target like a PDA or Nokia mobile phone. See my post about halfway down the page on pgforum.com here: http://www.paraglidingforum.com/viewtopic.php?t=5363 (the one by Alistair Dickie - that's me). I did not do anything about it, other than lots of googling, the occasional chat with other pilots on the way up to launch, or more often that not in the bombout.
Fast forward to 2011. There was another post on pgforum about a homebuilt vario design (http://www.paraglidingforum.com/viewtopic.php?t=36799) and then another about barometric pressure sensors in Android tablets (http://www.paraglidingforum.com/viewtopic.php?t=36347). One of my too many hobbies is java programming (see alistairdickie.com for some of my older stuff). Android programming is in Java. I got my wife a new Android phone the beginning of this year so I could check it out - well, she actually needed a new phone - checking out Android was a side benefit. I discoverd that there are a few paragliding apps for Android phones. Gaggle seems to be one of the most widely used (http://www.paraglidingforum.com/viewtopic.php?t=30548), but it is missing accurate vario functionality. My interest in a bluetooth vario was rekindled.
I started googling again in earnest. Were there any other bluetooth varios available? What was the state of bluetooth transmitter modules? How about microcontrollers? Most importantly, pressure sensors? What had other experimenters done? It all looked good. I worked out that in the five years since the initial concept there had been a number of advances:
- A few bluetooth varios had been built. The Flymaster F1 module (working only with their PDA software), and a few home built devices from kit components were examples. However, there was nothing quite like I had envisaged.
- Bluetooth transmitter modules had come a long way, in simplicity and price. Sparkfun has a bunch.
- Microcontrollers had become easier to program (C with free tools is now the standard, I would not have to frack around with Assembly), and much cheaper (like less than $5).
- Pressure sensors suitable for varios had become much cheaper. The BMP085 available from Sparkfun had a reasonable following, but there were new ones coming out from MEAS as well. Importantly, these new sensors were cheap (less than $10 to $20) and easy to interface with from microcontroller code.
- Other experimenters had built and posted code for simple varios. I found Hari Nair's site http://pixelproc.net/ to be the most amazing resource.